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Here's What You Need to Understand About Research Methodology

Deeptanshu D

Table of Contents

Research methodology involves a systematic and well-structured approach to conducting scholarly or scientific inquiries. Knowing the significance of research methodology and its different components is crucial as it serves as the basis for any study.

Typically, your research topic will start as a broad idea you want to investigate more thoroughly. Once you’ve identified a research problem and created research questions , you must choose the appropriate methodology and frameworks to address those questions effectively.

What is the definition of a research methodology?

Research methodology is the process or the way you intend to execute your study. The methodology section of a research paper outlines how you plan to conduct your study. It covers various steps such as collecting data, statistical analysis, observing participants, and other procedures involved in the research process

The methods section should give a description of the process that will convert your idea into a study. Additionally, the outcomes of your process must provide valid and reliable results resonant with the aims and objectives of your research. This thumb rule holds complete validity, no matter whether your paper has inclinations for qualitative or quantitative usage.

Studying research methods used in related studies can provide helpful insights and direction for your own research. Now easily discover papers related to your topic on SciSpace and utilize our AI research assistant, Copilot , to quickly review the methodologies applied in different papers.

Analyze and understand research methodologies faster with SciSpace Copilot

The need for a good research methodology

While deciding on your approach towards your research, the reason or factors you weighed in choosing a particular problem and formulating a research topic need to be validated and explained. A research methodology helps you do exactly that. Moreover, a good research methodology lets you build your argument to validate your research work performed through various data collection methods, analytical methods, and other essential points.

Just imagine it as a strategy documented to provide an overview of what you intend to do.

While undertaking any research writing or performing the research itself, you may get drifted in not something of much importance. In such a case, a research methodology helps you to get back to your outlined work methodology.

A research methodology helps in keeping you accountable for your work. Additionally, it can help you evaluate whether your work is in sync with your original aims and objectives or not. Besides, a good research methodology enables you to navigate your research process smoothly and swiftly while providing effective planning to achieve your desired results.

What is the basic structure of a research methodology?

Usually, you must ensure to include the following stated aspects while deciding over the basic structure of your research methodology:

1. Your research procedure

Explain what research methods you’re going to use. Whether you intend to proceed with quantitative or qualitative, or a composite of both approaches, you need to state that explicitly. The option among the three depends on your research’s aim, objectives, and scope.

2. Provide the rationality behind your chosen approach

Based on logic and reason, let your readers know why you have chosen said research methodologies. Additionally, you have to build strong arguments supporting why your chosen research method is the best way to achieve the desired outcome.

3. Explain your mechanism

The mechanism encompasses the research methods or instruments you will use to develop your research methodology. It usually refers to your data collection methods. You can use interviews, surveys, physical questionnaires, etc., of the many available mechanisms as research methodology instruments. The data collection method is determined by the type of research and whether the data is quantitative data(includes numerical data) or qualitative data (perception, morale, etc.) Moreover, you need to put logical reasoning behind choosing a particular instrument.

4. Significance of outcomes

The results will be available once you have finished experimenting. However, you should also explain how you plan to use the data to interpret the findings. This section also aids in understanding the problem from within, breaking it down into pieces, and viewing the research problem from various perspectives.

5. Reader’s advice

Anything that you feel must be explained to spread more awareness among readers and focus groups must be included and described in detail. You should not just specify your research methodology on the assumption that a reader is aware of the topic.  

All the relevant information that explains and simplifies your research paper must be included in the methodology section. If you are conducting your research in a non-traditional manner, give a logical justification and list its benefits.

6. Explain your sample space

Include information about the sample and sample space in the methodology section. The term "sample" refers to a smaller set of data that a researcher selects or chooses from a larger group of people or focus groups using a predetermined selection method. Let your readers know how you are going to distinguish between relevant and non-relevant samples. How you figured out those exact numbers to back your research methodology, i.e. the sample spacing of instruments, must be discussed thoroughly.

For example, if you are going to conduct a survey or interview, then by what procedure will you select the interviewees (or sample size in case of surveys), and how exactly will the interview or survey be conducted.

7. Challenges and limitations

This part, which is frequently assumed to be unnecessary, is actually very important. The challenges and limitations that your chosen strategy inherently possesses must be specified while you are conducting different types of research.

The importance of a good research methodology

You must have observed that all research papers, dissertations, or theses carry a chapter entirely dedicated to research methodology. This section helps maintain your credibility as a better interpreter of results rather than a manipulator.

A good research methodology always explains the procedure, data collection methods and techniques, aim, and scope of the research. In a research study, it leads to a well-organized, rationality-based approach, while the paper lacking it is often observed as messy or disorganized.

You should pay special attention to validating your chosen way towards the research methodology. This becomes extremely important in case you select an unconventional or a distinct method of execution.

Curating and developing a strong, effective research methodology can assist you in addressing a variety of situations, such as:

  • When someone tries to duplicate or expand upon your research after few years.
  • If a contradiction or conflict of facts occurs at a later time. This gives you the security you need to deal with these contradictions while still being able to defend your approach.
  • Gaining a tactical approach in getting your research completed in time. Just ensure you are using the right approach while drafting your research methodology, and it can help you achieve your desired outcomes. Additionally, it provides a better explanation and understanding of the research question itself.
  • Documenting the results so that the final outcome of the research stays as you intended it to be while starting.

Instruments you could use while writing a good research methodology

As a researcher, you must choose which tools or data collection methods that fit best in terms of the relevance of your research. This decision has to be wise.

There exists many research equipments or tools that you can use to carry out your research process. These are classified as:

a. Interviews (One-on-One or a Group)

An interview aimed to get your desired research outcomes can be undertaken in many different ways. For example, you can design your interview as structured, semi-structured, or unstructured. What sets them apart is the degree of formality in the questions. On the other hand, in a group interview, your aim should be to collect more opinions and group perceptions from the focus groups on a certain topic rather than looking out for some formal answers.

In surveys, you are in better control if you specifically draft the questions you seek the response for. For example, you may choose to include free-style questions that can be answered descriptively, or you may provide a multiple-choice type response for questions. Besides, you can also opt to choose both ways, deciding what suits your research process and purpose better.

c. Sample Groups

Similar to the group interviews, here, you can select a group of individuals and assign them a topic to discuss or freely express their opinions over that. You can simultaneously note down the answers and later draft them appropriately, deciding on the relevance of every response.

d. Observations

If your research domain is humanities or sociology, observations are the best-proven method to draw your research methodology. Of course, you can always include studying the spontaneous response of the participants towards a situation or conducting the same but in a more structured manner. A structured observation means putting the participants in a situation at a previously decided time and then studying their responses.

Of all the tools described above, it is you who should wisely choose the instruments and decide what’s the best fit for your research. You must not restrict yourself from multiple methods or a combination of a few instruments if appropriate in drafting a good research methodology.

Types of research methodology

A research methodology exists in various forms. Depending upon their approach, whether centered around words, numbers, or both, methodologies are distinguished as qualitative, quantitative, or an amalgamation of both.

1. Qualitative research methodology

When a research methodology primarily focuses on words and textual data, then it is generally referred to as qualitative research methodology. This type is usually preferred among researchers when the aim and scope of the research are mainly theoretical and explanatory.

The instruments used are observations, interviews, and sample groups. You can use this methodology if you are trying to study human behavior or response in some situations. Generally, qualitative research methodology is widely used in sociology, psychology, and other related domains.

2. Quantitative research methodology

If your research is majorly centered on data, figures, and stats, then analyzing these numerical data is often referred to as quantitative research methodology. You can use quantitative research methodology if your research requires you to validate or justify the obtained results.

In quantitative methods, surveys, tests, experiments, and evaluations of current databases can be advantageously used as instruments If your research involves testing some hypothesis, then use this methodology.

3. Amalgam methodology

As the name suggests, the amalgam methodology uses both quantitative and qualitative approaches. This methodology is used when a part of the research requires you to verify the facts and figures, whereas the other part demands you to discover the theoretical and explanatory nature of the research question.

The instruments for the amalgam methodology require you to conduct interviews and surveys, including tests and experiments. The outcome of this methodology can be insightful and valuable as it provides precise test results in line with theoretical explanations and reasoning.

The amalgam method, makes your work both factual and rational at the same time.

Final words: How to decide which is the best research methodology?

If you have kept your sincerity and awareness intact with the aims and scope of research well enough, you must have got an idea of which research methodology suits your work best.

Before deciding which research methodology answers your research question, you must invest significant time in reading and doing your homework for that. Taking references that yield relevant results should be your first approach to establishing a research methodology.

Moreover, you should never refrain from exploring other options. Before setting your work in stone, you must try all the available options as it explains why the choice of research methodology that you finally make is more appropriate than the other available options.

You should always go for a quantitative research methodology if your research requires gathering large amounts of data, figures, and statistics. This research methodology will provide you with results if your research paper involves the validation of some hypothesis.

Whereas, if  you are looking for more explanations, reasons, opinions, and public perceptions around a theory, you must use qualitative research methodology.The choice of an appropriate research methodology ultimately depends on what you want to achieve through your research.

Frequently Asked Questions (FAQs) about Research Methodology

1. how to write a research methodology.

You can always provide a separate section for research methodology where you should specify details about the methods and instruments used during the research, discussions on result analysis, including insights into the background information, and conveying the research limitations.

2. What are the types of research methodology?

There generally exists four types of research methodology i.e.

  • Observation
  • Experimental
  • Derivational

3. What is the true meaning of research methodology?

The set of techniques or procedures followed to discover and analyze the information gathered to validate or justify a research outcome is generally called Research Methodology.

4. Where lies the importance of research methodology?

Your research methodology directly reflects the validity of your research outcomes and how well-informed your research work is. Moreover, it can help future researchers cite or refer to your research if they plan to use a similar research methodology.

what to include in research proposal methodology

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How to Write a Research Proposal: A Step-by-Step

By Danesh Ramuthi , Nov 29, 2023

How to Write a Research Proposal

A research proposal is a structured outline for a planned study on a specific topic. It serves as a roadmap, guiding researchers through the process of converting their research idea into a feasible project. 

The aim of a research proposal is multifold: it articulates the research problem, establishes a theoretical framework, outlines the research methodology and highlights the potential significance of the study. Importantly, it’s a critical tool for scholars seeking grant funding or approval for their research projects.

Crafting a good research proposal requires not only understanding your research topic and methodological approaches but also the ability to present your ideas clearly and persuasively. Explore Venngage’s Proposal Maker and Research Proposals Templates to begin your journey in writing a compelling research proposal.

What to include in a research proposal?

In a research proposal, include a clear statement of your research question or problem, along with an explanation of its significance. This should be followed by a literature review that situates your proposed study within the context of existing research. 

Your proposal should also outline the research methodology, detailing how you plan to conduct your study, including data collection and analysis methods.

Additionally, include a theoretical framework that guides your research approach, a timeline or research schedule, and a budget if applicable. It’s important to also address the anticipated outcomes and potential implications of your study. A well-structured research proposal will clearly communicate your research objectives, methods and significance to the readers.

Light Blue Shape Semiotic Analysis Research Proposal

How to format a research proposal?

Formatting a research proposal involves adhering to a structured outline to ensure clarity and coherence. While specific requirements may vary, a standard research proposal typically includes the following elements:

  • Title Page: Must include the title of your research proposal, your name and affiliations. The title should be concise and descriptive of your proposed research.
  • Abstract: A brief summary of your proposal, usually not exceeding 250 words. It should highlight the research question, methodology and the potential impact of the study.
  • Introduction: Introduces your research question or problem, explains its significance, and states the objectives of your study.
  • Literature review: Here, you contextualize your research within existing scholarship, demonstrating your knowledge of the field and how your research will contribute to it.
  • Methodology: Outline your research methods, including how you will collect and analyze data. This section should be detailed enough to show the feasibility and thoughtfulness of your approach.
  • Timeline: Provide an estimated schedule for your research, breaking down the process into stages with a realistic timeline for each.
  • Budget (if applicable): If your research requires funding, include a detailed budget outlining expected cost.
  • References/Bibliography: List all sources referenced in your proposal in a consistent citation style.

Green And Orange Modern Research Proposal

How to write a research proposal in 11 steps?

Writing a research proposal in structured steps ensures a comprehensive and coherent presentation of your research project. Let’s look at the explanation for each of the steps here:  

Step 1: Title and Abstract Step 2: Introduction Step 3: Research objectives Step 4: Literature review Step 5: Methodology Step 6: Timeline Step 7: Resources Step 8: Ethical considerations Step 9: Expected outcomes and significance Step 10: References Step 11: Appendices

Step 1: title and abstract.

Select a concise, descriptive title and write an abstract summarizing your research question, objectives, methodology and expected outcomes​​. The abstract should include your research question, the objectives you aim to achieve, the methodology you plan to employ and the anticipated outcomes. 

Step 2: Introduction

In this section, introduce the topic of your research, emphasizing its significance and relevance to the field. Articulate the research problem or question in clear terms and provide background context, which should include an overview of previous research in the field.

Step 3: Research objectives

Here, you’ll need to outline specific, clear and achievable objectives that align with your research problem. These objectives should be well-defined, focused and measurable, serving as the guiding pillars for your study. They help in establishing what you intend to accomplish through your research and provide a clear direction for your investigation.

Step 4: Literature review

In this part, conduct a thorough review of existing literature related to your research topic. This involves a detailed summary of key findings and major contributions from previous research. Identify existing gaps in the literature and articulate how your research aims to fill these gaps. The literature review not only shows your grasp of the subject matter but also how your research will contribute new insights or perspectives to the field.

Step 5: Methodology

Describe the design of your research and the methodologies you will employ. This should include detailed information on data collection methods, instruments to be used and analysis techniques. Justify the appropriateness of these methods for your research​​.

Step 6: Timeline

Construct a detailed timeline that maps out the major milestones and activities of your research project. Break the entire research process into smaller, manageable tasks and assign realistic time frames to each. This timeline should cover everything from the initial research phase to the final submission, including periods for data collection, analysis and report writing. 

It helps in ensuring your project stays on track and demonstrates to reviewers that you have a well-thought-out plan for completing your research efficiently.

Step 7: Resources

Identify all the resources that will be required for your research, such as specific databases, laboratory equipment, software or funding. Provide details on how these resources will be accessed or acquired. 

If your research requires funding, explain how it will be utilized effectively to support various aspects of the project. 

Step 8: Ethical considerations

Address any ethical issues that may arise during your research. This is particularly important for research involving human subjects. Describe the measures you will take to ensure ethical standards are maintained, such as obtaining informed consent, ensuring participant privacy, and adhering to data protection regulations. 

Here, in this section you should reassure reviewers that you are committed to conducting your research responsibly and ethically.

Step 9: Expected outcomes and significance

Articulate the expected outcomes or results of your research. Explain the potential impact and significance of these outcomes, whether in advancing academic knowledge, influencing policy or addressing specific societal or practical issues. 

Step 10: References

Compile a comprehensive list of all the references cited in your proposal. Adhere to a consistent citation style (like APA or MLA) throughout your document. The reference section not only gives credit to the original authors of your sourced information but also strengthens the credibility of your proposal.

Step 11: Appendices

Include additional supporting materials that are pertinent to your research proposal. This can be survey questionnaires, interview guides, detailed data analysis plans or any supplementary information that supports the main text. 

Appendices provide further depth to your proposal, showcasing the thoroughness of your preparation.

Beige And Dark Green Minimalist Research Proposal

Research proposal FAQs

1. how long should a research proposal be.

The length of a research proposal can vary depending on the requirements of the academic institution, funding body or specific guidelines provided. Generally, research proposals range from 500 to 1500 words or about one to a few pages long. It’s important to provide enough detail to clearly convey your research idea, objectives and methodology, while being concise. Always check

2. Why is the research plan pivotal to a research project?

The research plan is pivotal to a research project because it acts as a blueprint, guiding every phase of the study. It outlines the objectives, methodology, timeline and expected outcomes, providing a structured approach and ensuring that the research is systematically conducted. 

A well-crafted plan helps in identifying potential challenges, allocating resources efficiently and maintaining focus on the research goals. It is also essential for communicating the project’s feasibility and importance to stakeholders, such as funding bodies or academic supervisors.

Simple Minimalist White Research Proposal

Mastering how to write a research proposal is an essential skill for any scholar, whether in social and behavioral sciences, academic writing or any field requiring scholarly research. From this article, you have learned key components, from the literature review to the research design, helping you develop a persuasive and well-structured proposal.

Remember, a good research proposal not only highlights your proposed research and methodology but also demonstrates its relevance and potential impact.

For additional support, consider utilizing Venngage’s Proposal Maker and Research Proposals Templates , valuable tools in crafting a compelling proposal that stands out.

Whether it’s for grant funding, a research paper or a dissertation proposal, these resources can assist in transforming your research idea into a successful submission.

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What Is a Research Proposal?

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When applying for a research grant or scholarship, or, just before you start a major research project, you may be asked to write a preliminary document that includes basic information about your future research. This is the information that is usually needed in your proposal:

  • The topic and goal of the research project.
  • The kind of result expected from the research.
  • The theory or framework in which the research will be done and presented.
  • What kind of methods will be used (statistical, empirical, etc.).
  • Short reference on the preliminary scholarship and why your research project is needed; how will it continue/justify/disprove the previous scholarship.
  • How much will the research project cost; how will it be budgeted (what for the money will be spent).
  • Why is it you who can do this research and not somebody else.

Most agencies that offer scholarships or grants provide information about the required format of the proposal. It may include filling out templates, types of information they need, suggested/maximum length of the proposal, etc.

Research proposal formats vary depending on the size of the planned research, the number of participants, the discipline, the characteristics of the research, etc. The following outline assumes an individual researcher. This is just a SAMPLE; several other ways are equally good and can be successful. If possible, discuss your research proposal with an expert in writing, a professor, your colleague, another student who already wrote successful proposals, etc.

Author, author's affiliation

Introduction:

  • Explain the topic and why you chose it. If possible explain your goal/outcome of the research . How much time you need to complete the research?

Previous scholarship:

  • Give a brief summary of previous scholarship and explain why your topic and goals are important.
  • Relate your planned research to previous scholarship. What will your research add to our knowledge of the topic.

Specific issues to be investigated:

  • Break down the main topic into smaller research questions. List them one by one and explain why these questions need to be investigated. Relate them to previous scholarship.
  • Include your hypothesis into the descriptions of the detailed research issues if you have one. Explain why it is important to justify your hypothesis.

Methodology:

  • This part depends of the methods conducted in the research process. List the methods; explain how the results will be presented; how they will be assessed.
  • Explain what kind of results will justify or  disprove your hypothesis. 
  • Explain how much money you need.
  • Explain the details of the budget (how much you want to spend for what).

Conclusion:

  • Describe why your research is important.

References:

  • List the sources you have used for writing the research proposal, including a few main citations of the preliminary scholarship.

what to include in research proposal methodology

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How to prepare a Research Proposal

Health research, medical education and clinical practice form the three pillars of modern day medical practice. As one authority rightly put it: ‘Health research is not a luxury, but an essential need that no nation can afford to ignore’. Health research can and should be pursued by a broad range of people. Even if they do not conduct research themselves, they need to grasp the principles of the scientific method to understand the value and limitations of science and to be able to assess and evaluate results of research before applying them. This review paper aims to highlight the essential concepts to the students and beginning researchers and sensitize and motivate the readers to access the vast literature available on research methodologies.

Most students and beginning researchers do not fully understand what a research proposal means, nor do they understand its importance. 1 A research proposal is a detailed description of a proposed study designed to investigate a given problem. 2

A research proposal is intended to convince others that you have a worthwhile research project and that you have the competence and the work-plan to complete it. Broadly the research proposal must address the following questions regardless of your research area and the methodology you choose: What you plan to accomplish, why do you want to do it and how are you going to do it. 1 The aim of this article is to highlight the essential concepts and not to provide extensive details about this topic.

The elements of a research proposal are highlighted below:

1. Title: It should be concise and descriptive. It must be informative and catchy. An effective title not only prick’s the readers interest, but also predisposes him/her favorably towards the proposal. Often titles are stated in terms of a functional relationship, because such titles clearly indicate the independent and dependent variables. 1 The title may need to be revised after completion of writing of the protocol to reflect more closely the sense of the study. 3

2. Abstract: It is a brief summary of approximately 300 words. It should include the main research question, the rationale for the study, the hypothesis (if any) and the method. Descriptions of the method may include the design, procedures, the sample and any instruments that will be used. 1 It should stand on its own, and not refer the reader to points in the project description. 3

3. Introduction: The introduction provides the readers with the background information. Its purpose is to establish a framework for the research, so that readers can understand how it relates to other research. 4 It should answer the question of why the research needs to be done and what will be its relevance. It puts the proposal in context. 3

The introduction typically begins with a statement of the research problem in precise and clear terms. 1

The importance of the statement of the research problem 5 : The statement of the problem is the essential basis for the construction of a research proposal (research objectives, hypotheses, methodology, work plan and budget etc). It is an integral part of selecting a research topic. It will guide and put into sharper focus the research design being considered for solving the problem. It allows the investigator to describe the problem systematically, to reflect on its importance, its priority in the country and region and to point out why the proposed research on the problem should be undertaken. It also facilitates peer review of the research proposal by the funding agencies.

Then it is necessary to provide the context and set the stage for the research question in such a way as to show its necessity and importance. 1 This step is necessary for the investigators to familiarize themselves with existing knowledge about the research problem and to find out whether or not others have investigated the same or similar problems. This step is accomplished by a thorough and critical review of the literature and by personal communication with experts. 5 It helps further understanding of the problem proposed for research and may lead to refining the statement of the problem, to identify the study variables and conceptualize their relationships, and in formulation and selection of a research hypothesis. 5 It ensures that you are not "re-inventing the wheel" and demonstrates your understanding of the research problem. It gives due credit to those who have laid the groundwork for your proposed research. 1 In a proposal, the literature review is generally brief and to the point. The literature selected should be pertinent and relevant. 6

Against this background, you then present the rationale of the proposed study and clearly indicate why it is worth doing.

4. Objectives: Research objectives are the goals to be achieved by conducting the research. 5 They may be stated as ‘general’ and ‘specific’.

The general objective of the research is what is to be accomplished by the research project, for example, to determine whether or not a new vaccine should be incorporated in a public health program.

The specific objectives relate to the specific research questions the investigator wants to answer through the proposed study and may be presented as primary and secondary objectives, for example, primary: To determine the degree of protection that is attributable to the new vaccine in a study population by comparing the vaccinated and unvaccinated groups. 5 Secondary: To study the cost-effectiveness of this programme.

Young investigators are advised to resist the temptation to put too many objectives or over-ambitious objectives that cannot be adequately achieved by the implementation of the protocol. 3

5. Variables: During the planning stage, it is necessary to identify the key variables of the study and their method of measurement and unit of measurement must be clearly indicated. Four types of variables are important in research 5 :

a. Independent variables: variables that are manipulated or treated in a study in order to see what effect differences in them will have on those variables proposed as being dependent on them. The different synonyms for the term ‘independent variable’ which are used in literature are: cause, input, predisposing factor, risk factor, determinant, antecedent, characteristic and attribute.

b. Dependent variables: variables in which changes are results of the level or amount of the independent variable or variables.

Synonyms: effect, outcome, consequence, result, condition, disease.

c. Confounding or intervening variables: variables that should be studied because they may influence or ‘mix’ the effect of the independent variables. For instance, in a study of the effect of measles (independent variable) on child mortality (dependent variable), the nutritional status of the child may play an intervening (confounding) role.

d. Background variables: variables that are so often of relevance in investigations of groups or populations that they should be considered for possible inclusion in the study. For example sex, age, ethnic origin, education, marital status, social status etc.

The objective of research is usually to determine the effect of changes in one or more independent variables on one or more dependent variables. For example, a study may ask "Will alcohol intake (independent variable) have an effect on development of gastric ulcer (dependent variable)?"

Certain variables may not be easy to identify. The characteristics that define these variables must be clearly identified for the purpose of the study.

6. Questions and/ or hypotheses: If you as a researcher know enough to make prediction concerning what you are studying, then the hypothesis may be formulated. A hypothesis can be defined as a tentative prediction or explanation of the relationship between two or more variables. In other words, the hypothesis translates the problem statement into a precise, unambiguous prediction of expected outcomes. Hypotheses are not meant to be haphazard guesses, but should reflect the depth of knowledge, imagination and experience of the investigator. 5 In the process of formulating the hypotheses, all variables relevant to the study must be identified. For example: "Health education involving active participation by mothers will produce more positive changes in child feeding than health education based on lectures". Here the independent variable is types of health education and the dependent variable is changes in child feeding.

A research question poses a relationship between two or more variables but phrases the relationship as a question; a hypothesis represents a declarative statement of the relations between two or more variables. 7

For exploratory or phenomenological research, you may not have any hypothesis (please do not confuse the hypothesis with the statistical null hypothesis). 1 Questions are relevant to normative or census type research (How many of them are there? Is there a relationship between them?). Deciding whether to use questions or hypotheses depends on factors such as the purpose of the study, the nature of the design and methodology, and the audience of the research (at times even the outlook and preference of the committee members, particularly the Chair). 6

7. Methodology: The method section is very important because it tells your research Committee how you plan to tackle your research problem. The guiding principle for writing the Methods section is that it should contain sufficient information for the reader to determine whether the methodology is sound. Some even argue that a good proposal should contain sufficient details for another qualified researcher to implement the study. 1 Indicate the methodological steps you will take to answer every question or to test every hypothesis illustrated in the Questions/hypotheses section. 6 It is vital that you consult a biostatistician during the planning stage of your study, 8 to resolve the methodological issues before submitting the proposal.

This section should include:

Research design: The selection of the research strategy is the core of research design and is probably the single most important decision the investigator has to make. The choice of the strategy, whether descriptive, analytical, experimental, operational or a combination of these depend on a number of considerations, 5 but this choice must be explained in relation to the study objectives. 3

Research subjects or participants: Depending on the type of your study, the following questions should be answered 3 , 5

  • - What are the criteria for inclusion or selection?
  • - What are the criteria for exclusion?
  • - What is the sampling procedure you will use so as to ensure representativeness and reliability of the sample and to minimize sampling errors? The key reason for being concerned with sampling is the issue of validity-both internal and external of the study results. 9
  • - Will there be use of controls in your study? Controls or comparison groups are used in scientific research in order to increase the validity of the conclusions. Control groups are necessary in all analytical epidemiological studies, in experimental studies of drug trials, in research on effects of intervention programmes and disease control measures and in many other investigations. Some descriptive studies (studies of existing data, surveys) may not require control groups.
  • - What are the criteria for discontinuation?

Sample size: The proposal should provide information and justification (basis on which the sample size is calculated) about sample size in the methodology section. 3 A larger sample size than needed to test the research hypothesis increases the cost and duration of the study and will be unethical if it exposes human subjects to any potential unnecessary risk without additional benefit. A smaller sample size than needed can also be unethical as it exposes human subjects to risk with no benefit to scientific knowledge. Calculation of sample size has been made easy by computer software programmes, but the principles underlying the estimation should be well understood.

Interventions: If an intervention is introduced, a description must be given of the drugs or devices (proprietary names, manufacturer, chemical composition, dose, frequency of administration) if they are already commercially available. If they are in phases of experimentation or are already commercially available but used for other indications, information must be provided on available pre-clinical investigations in animals and/or results of studies already conducted in humans (in such cases, approval of the drug regulatory agency in the country is needed before the study). 3

Ethical issues 3 : Ethical considerations apply to all types of health research. Before the proposal is submitted to the Ethics Committee for approval, two important documents mentioned below (where appropriate) must be appended to the proposal. In additions, there is another vital issue of Conflict of Interest, wherein the researchers should furnish a statement regarding the same.

The Informed consent form (informed decision-making): A consent form, where appropriate, must be developed and attached to the proposal. It should be written in the prospective subjects’ mother tongue and in simple language which can be easily understood by the subject. The use of medical terminology should be avoided as far as possible. Special care is needed when subjects are illiterate. It should explain why the study is being done and why the subject has been asked to participate. It should describe, in sequence, what will happen in the course of the study, giving enough detail for the subject to gain a clear idea of what to expect. It should clarify whether or not the study procedures offer any benefits to the subject or to others, and explain the nature, likelihood and treatment of anticipated discomfort or adverse effects, including psychological and social risks, if any. Where relevant, a comparison with risks posed by standard drugs or treatment must be included. If the risks are unknown or a comparative risk cannot be given it should be so stated. It should indicate that the subject has the right to withdraw from the study at any time without, in any way, affecting his/her further medical care. It should assure the participant of confidentiality of the findings.

Ethics checklist: The proposal must describe the measures that will be undertaken to ensure that the proposed research is carried out in accordance with the World Medical Association Declaration of Helsinki on Ethical Principles for Medical research involving Human Subjects. 10 It must answer the following questions:

  • • Is the research design adequate to provide answers to the research question? It is unethical to expose subjects to research that will have no value.
  • • Is the method of selection of research subjects justified? The use of vulnerable subjects as research participants needs special justification. Vulnerable subjects include those in prison, minors and persons with mental disability. In international research it is important to mention that the population in which the study is conducted will benefit from any potential outcome of the research and the research is not being conducted solely for the benefit of some other population. Justification is needed for any inducement, financial or otherwise, for the participants to be enrolled in the study.
  • • Are the interventions justified, in terms of risk/benefit ratio? Risks are not limited to physical harm. Psychological and social risks must also be considered.
  • • For observations made, have measures been taken to ensure confidentiality?

Research setting 5 : The research setting includes all the pertinent facets of the study, such as the population to be studied (sampling frame), the place and time of study.

Study instruments 3 , 5 : Instruments are the tools by which the data are collected. For validated questionnaires/interview schedules, reference to published work should be given and the instrument appended to the proposal. For new a questionnaire which is being designed specifically for your study the details about preparing, precoding and pretesting of questionnaire should be furnished and the document appended to the proposal. Descriptions of other methods of observations like medical examination, laboratory tests and screening procedures is necessary- for established procedures, reference of published work cited but for new or modified procedure, an adequate description is necessary with justification for the same.

Collection of data: A short description of the protocol of data collection. For example, in a study on blood pressure measurement: time of participant arrival, rest for 5p. 10 minutes, which apparatus (standard calibrated) to be used, in which room to take measurement, measurement in sitting or lying down position, how many measurements, measurement in which arm first (whether this is going to be randomized), details of cuff and its placement, who will take the measurement. This minimizes the possibility of confusion, delays and errors.

Data analysis: The description should include the design of the analysis form, plans for processing and coding the data and the choice of the statistical method to be applied to each data. What will be the procedures for accounting for missing, unused or spurious data?

Monitoring, supervision and quality control: Detailed statement about the all logistical issues to satisfy the requirements of Good Clinical Practices (GCP), protocol procedures, responsibilities of each member of the research team, training of study investigators, steps taken to assure quality control (laboratory procedures, equipment calibration etc)

Gantt chart: A Gantt chart is an overview of tasks/proposed activities and a time frame for the same. You put weeks, days or months at one side, and the tasks at the other. You draw fat lines to indicate the period the task will be performed to give a timeline for your research study (take help of tutorial on youtube). 11

Significance of the study: Indicate how your research will refine, revise or extend existing knowledge in the area under investigation. How will it benefit the concerned stakeholders? What could be the larger implications of your research study?

Dissemination of the study results: How do you propose to share the findings of your study with professional peers, practitioners, participants and the funding agency?

Budget: A proposal budget with item wise/activity wise breakdown and justification for the same. Indicate how will the study be financed.

References: The proposal should end with relevant references on the subject. For web based search include the date of access for the cited website, for example: add the sentence "accessed on June 10, 2008".

Appendixes: Include the appropriate appendixes in the proposal. For example: Interview protocols, sample of informed consent forms, cover letters sent to appropriate stakeholders, official letters for permission to conduct research. Regarding original scales or questionnaires, if the instrument is copyrighted then permission in writing to reproduce the instrument from the copyright holder or proof of purchase of the instrument must be submitted.

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Writing Research Proposals

The research proposal is your opportunity to show that you—and only you!—are the perfect person to take on your specific project. After reading your research proposal, readers should be confident that…

  • You have thoughtfully crafted and designed this project;
  • You have the necessary background to complete this project;
  • You have the proper support system in place;
  • You know exactly what you need to complete this project and how to do so; and
  • With this funding in hand, you can be on your way to a meaningful research experience and a significant contribution to your field.

Research proposals typically include the following components:

  • Why is your project important? How does it contribute to the field or to society? What do you hope to prove?
  • This section includes the project design, specific methodology, your specific role and responsibilities, steps you will take to execute the project, etc. Here you will show the committee the way that you think by explaining both how you have conceived the project and how you intend to carry it out.
  • Please be specific in the project dates/how much time you need to carry out the proposed project. The scope of the project should clearly match the timeframe in which you propose to complete it!
  • Funding agencies like to know how their funding will be used. Including this information will demonstrate that you have thoughtfully designed the project and know of all of the anticipated expenses required to see it through to completion.
  • It is important that you have a support system on hand when conducting research, especially as an undergraduate. There are often surprises and challenges when working on a long-term research project and the selection committee wants to be sure that you have the support system you need to both be successful in your project and also have a meaningful research experience. 
  • Some questions to consider are: How often do you intend to meet with your advisor(s)? (This may vary from project to project based on the needs of the student and the nature of the research.) What will your mode of communication be? Will you be attending (or even presenting at) lab meetings? 

Don’t be afraid to also include relevant information about your background and advocate for yourself! Do you have skills developed in a different research experience (or leadership position, job, coursework, etc.) that you could apply to the project in question? Have you already learned about and experimented with a specific method of analysis in class and are now ready to apply it to a different situation? If you already have experience with this professor/lab, please be sure to include those details in your proposal! That will show the selection committee that you are ready to hit the ground running!

Lastly, be sure to know who your readers are so that you can tailor the field-specific language of your proposal accordingly. If the selection committee are specialists in your field, you can feel free to use the jargon of that field; but if your proposal will be evaluated by an interdisciplinary committee (this is common), you might take a bit longer explaining the state of the field, specific concepts, and certainly spelling out any acronyms.

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  • How to Write a Research Proposal | Examples & Templates

How to Write a Research Proposal | Examples & Templates

Published on 30 October 2022 by Shona McCombes and Tegan George. Revised on 13 June 2023.

Structure of a research proposal

A research proposal describes what you will investigate, why it’s important, and how you will conduct your research.

The format of a research proposal varies between fields, but most proposals will contain at least these elements:

Introduction

Literature review.

  • Research design

Reference list

While the sections may vary, the overall objective is always the same. A research proposal serves as a blueprint and guide for your research plan, helping you get organised and feel confident in the path forward you choose to take.

Table of contents

Research proposal purpose, research proposal examples, research design and methods, contribution to knowledge, research schedule, frequently asked questions.

Academics often have to write research proposals to get funding for their projects. As a student, you might have to write a research proposal as part of a grad school application , or prior to starting your thesis or dissertation .

In addition to helping you figure out what your research can look like, a proposal can also serve to demonstrate why your project is worth pursuing to a funder, educational institution, or supervisor.

Research proposal length

The length of a research proposal can vary quite a bit. A bachelor’s or master’s thesis proposal can be just a few pages, while proposals for PhD dissertations or research funding are usually much longer and more detailed. Your supervisor can help you determine the best length for your work.

One trick to get started is to think of your proposal’s structure as a shorter version of your thesis or dissertation , only without the results , conclusion and discussion sections.

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Writing a research proposal can be quite challenging, but a good starting point could be to look at some examples. We’ve included a few for you below.

  • Example research proposal #1: ‘A Conceptual Framework for Scheduling Constraint Management’
  • Example research proposal #2: ‘ Medical Students as Mediators of Change in Tobacco Use’

Like your dissertation or thesis, the proposal will usually have a title page that includes:

  • The proposed title of your project
  • Your supervisor’s name
  • Your institution and department

The first part of your proposal is the initial pitch for your project. Make sure it succinctly explains what you want to do and why.

Your introduction should:

  • Introduce your topic
  • Give necessary background and context
  • Outline your  problem statement  and research questions

To guide your introduction , include information about:

  • Who could have an interest in the topic (e.g., scientists, policymakers)
  • How much is already known about the topic
  • What is missing from this current knowledge
  • What new insights your research will contribute
  • Why you believe this research is worth doing

As you get started, it’s important to demonstrate that you’re familiar with the most important research on your topic. A strong literature review  shows your reader that your project has a solid foundation in existing knowledge or theory. It also shows that you’re not simply repeating what other people have already done or said, but rather using existing research as a jumping-off point for your own.

In this section, share exactly how your project will contribute to ongoing conversations in the field by:

  • Comparing and contrasting the main theories, methods, and debates
  • Examining the strengths and weaknesses of different approaches
  • Explaining how will you build on, challenge, or synthesise prior scholarship

Following the literature review, restate your main  objectives . This brings the focus back to your own project. Next, your research design or methodology section will describe your overall approach, and the practical steps you will take to answer your research questions.

To finish your proposal on a strong note, explore the potential implications of your research for your field. Emphasise again what you aim to contribute and why it matters.

For example, your results might have implications for:

  • Improving best practices
  • Informing policymaking decisions
  • Strengthening a theory or model
  • Challenging popular or scientific beliefs
  • Creating a basis for future research

Last but not least, your research proposal must include correct citations for every source you have used, compiled in a reference list . To create citations quickly and easily, you can use our free APA citation generator .

Some institutions or funders require a detailed timeline of the project, asking you to forecast what you will do at each stage and how long it may take. While not always required, be sure to check the requirements of your project.

Here’s an example schedule to help you get started. You can also download a template at the button below.

Download our research schedule template

If you are applying for research funding, chances are you will have to include a detailed budget. This shows your estimates of how much each part of your project will cost.

Make sure to check what type of costs the funding body will agree to cover. For each item, include:

  • Cost : exactly how much money do you need?
  • Justification : why is this cost necessary to complete the research?
  • Source : how did you calculate the amount?

To determine your budget, think about:

  • Travel costs : do you need to go somewhere to collect your data? How will you get there, and how much time will you need? What will you do there (e.g., interviews, archival research)?
  • Materials : do you need access to any tools or technologies?
  • Help : do you need to hire any research assistants for the project? What will they do, and how much will you pay them?

Once you’ve decided on your research objectives , you need to explain them in your paper, at the end of your problem statement.

Keep your research objectives clear and concise, and use appropriate verbs to accurately convey the work that you will carry out for each one.

I will compare …

A research aim is a broad statement indicating the general purpose of your research project. It should appear in your introduction at the end of your problem statement , before your research objectives.

Research objectives are more specific than your research aim. They indicate the specific ways you’ll address the overarching aim.

A PhD, which is short for philosophiae doctor (doctor of philosophy in Latin), is the highest university degree that can be obtained. In a PhD, students spend 3–5 years writing a dissertation , which aims to make a significant, original contribution to current knowledge.

A PhD is intended to prepare students for a career as a researcher, whether that be in academia, the public sector, or the private sector.

A master’s is a 1- or 2-year graduate degree that can prepare you for a variety of careers.

All master’s involve graduate-level coursework. Some are research-intensive and intend to prepare students for further study in a PhD; these usually require their students to write a master’s thesis . Others focus on professional training for a specific career.

Critical thinking refers to the ability to evaluate information and to be aware of biases or assumptions, including your own.

Like information literacy , it involves evaluating arguments, identifying and solving problems in an objective and systematic way, and clearly communicating your ideas.

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Chapter 14: The Research Proposal

14.3 Components of a Research Proposal

Krathwohl (2005) suggests and describes a variety of components to include in a research proposal. The following sections – Introductions, Background and significance, Literature Review; Research design and methods, Preliminary suppositions and implications; and Conclusion present these components in a suggested template for you to follow in the preparation of your research proposal.

Introduction

The introduction sets the tone for what follows in your research proposal – treat it as the initial pitch of your idea. After reading the introduction your reader should:

  • understand what it is you want to do;
  • have a sense of your passion for the topic; and
  • be excited about the study’s possible outcomes.

As you begin writing your research proposal, it is helpful to think of the introduction as a narrative of what it is you want to do, written in one to three paragraphs. Within those one to three paragraphs, it is important to briefly answer the following questions:

  • What is the central research problem?
  • How is the topic of your research proposal related to the problem?
  • What methods will you utilize to analyze the research problem?
  • Why is it important to undertake this research? What is the significance of your proposed research? Why are the outcomes of your proposed research important? Whom are they important?

Note : You may be asked by your instructor to include an abstract with your research proposal. In such cases, an abstract should provide an overview of what it is you plan to study, your main research question, a brief explanation of your methods to answer the research question, and your expected findings. All of this information must be carefully crafted in 150 to 250 words. A word of advice is to save the writing of your abstract until the very end of your research proposal preparation. If you are asked to provide an abstract, you should include 5 to 7 key words that are of most relevance to your study. List these in order of relevance.

Background and significance

The purpose of this section is to explain the context of your proposal and to describe, in detail, why it is important to undertake this research. Assume that the person or people who will read your research proposal know nothing or very little about the research problem. While you do not need to include all knowledge you have learned about your topic in this section, it is important to ensure that you include the most relevant material that will help to explain the goals of your research.

While there are no hard and fast rules, you should attempt to address some or all of the following key points:

  • State the research problem and provide a more thorough explanation about the purpose of the study than what you stated in the introduction.
  • Present the rationale for the proposed research study. Clearly indicate why this research is worth doing. Answer the “so what?” question.
  • Describe the major issues or problems to be addressed by your research. Do not forget to explain how and in what ways your proposed research builds upon previous related research.
  • Explain how you plan to go about conducting your research.
  • Clearly identify the key or most relevant sources of research you intend to use and explain how they will contribute to your analysis of the topic.
  • Set the boundaries of your proposed research, in order to provide a clear focus. Where appropriate, state not only what you will study, but what will be excluded from your study.
  • Provide clear definitions of key concepts and terms. Since key concepts and terms often have numerous definitions, make sure you state which definition you will be utilizing in your research.

Literature review

This key component of the research proposal is the most time-consuming aspect in the preparation of your research proposal. As described in Chapter 5 , the literature review provides the background to your study and demonstrates the significance of the proposed research. Specifically, it is a review and synthesis of prior research that is related to the problem you are setting forth to investigate. Essentially, your goal in the literature review is to place your research study within the larger whole of what has been studied in the past, while demonstrating to your reader that your work is original, innovative, and adds to the larger whole.

As the literature review is information dense, it is essential that this section be intelligently structured to enable your reader to grasp the key arguments underpinning your study. However, this can be easier to state and harder to do, simply due to the fact there is usually a plethora of related research to sift through. Consequently, a good strategy for writing the literature review is to break the literature into conceptual categories or themes, rather than attempting to describe various groups of literature you reviewed. Chapter 5   describes a variety of methods to help you organize the themes.

Here are some suggestions on how to approach the writing of your literature review:

  • Think about what questions other researchers have asked, what methods they used, what they found, and what they recommended based upon their findings.
  • Do not be afraid to challenge previous related research findings and/or conclusions.
  • Assess what you believe to be missing from previous research and explain how your research fills in this gap and/or extends previous research.

It is important to note that a significant challenge related to undertaking a literature review is knowing when to stop. As such, it is important to know when you have uncovered the key conceptual categories underlying your research topic. Generally, when you start to see repetition in the conclusions or recommendations, you can have confidence that you have covered all of the significant conceptual categories in your literature review. However, it is also important to acknowledge that researchers often find themselves returning to the literature as they collect and analyze their data. For example, an unexpected finding may develop as you collect and/or analyze the data; in this case, it is important to take the time to step back and review the literature again, to ensure that no other researchers have found a similar finding. This may include looking to research outside your field.

This situation occurred with one of this textbook’s authors’ research related to community resilience. During the interviews, the researchers heard many participants discuss individual resilience factors and how they believed these individual factors helped make the community more resilient, overall. Sheppard and Williams (2016) had not discovered these individual factors in their original literature review on community and environmental resilience. However, when they returned to the literature to search for individual resilience factors, they discovered a small body of literature in the child and youth psychology field. Consequently, Sheppard and Williams had to go back and add a new section to their literature review on individual resilience factors. Interestingly, their research appeared to be the first research to link individual resilience factors with community resilience factors.

Research design and methods

The objective of this section of the research proposal is to convince the reader that your overall research design and methods of analysis will enable you to solve the research problem you have identified and also enable you to accurately and effectively interpret the results of your research. Consequently, it is critical that the research design and methods section is well-written, clear, and logically organized. This demonstrates to your reader that you know what you are going to do and how you are going to do it. Overall, you want to leave your reader feeling confident that you have what it takes to get this research study completed in a timely fashion.

Essentially, this section of the research proposal should be clearly tied to the specific objectives of your study; however, it is also important to draw upon and include examples from the literature review that relate to your design and intended methods. In other words, you must clearly demonstrate how your study utilizes and builds upon past studies, as it relates to the research design and intended methods. For example, what methods have been used by other researchers in similar studies?

While it is important to consider the methods that other researchers have employed, it is equally, if not more, important to consider what methods have not been but could be employed. Remember, the methods section is not simply a list of tasks to be undertaken. It is also an argument as to why and how the tasks you have outlined will help you investigate the research problem and answer your research question(s).

Tips for writing the research design and methods section:

Specify the methodological approaches you intend to employ to obtain information and the techniques you will use to analyze the data.

Specify the research operations you will undertake and the way you will interpret the results of those operations in relation to the research problem.

Go beyond stating what you hope to achieve through the methods you have chosen. State how you will actually implement the methods (i.e., coding interview text, running regression analysis, etc.).

Anticipate and acknowledge any potential barriers you may encounter when undertaking your research, and describe how you will address these barriers.

Explain where you believe you will find challenges related to data collection, including access to participants and information.

Preliminary suppositions and implications

The purpose of this section is to argue how you anticipate that your research will refine, revise, or extend existing knowledge in the area of your study. Depending upon the aims and objectives of your study, you should also discuss how your anticipated findings may impact future research. For example, is it possible that your research may lead to a new policy, theoretical understanding, or method for analyzing data? How might your study influence future studies? What might your study mean for future practitioners working in the field? Who or what might benefit from your study? How might your study contribute to social, economic or environmental issues? While it is important to think about and discuss possibilities such as these, it is equally important to be realistic in stating your anticipated findings. In other words, you do not want to delve into idle speculation. Rather, the purpose here is to reflect upon gaps in the current body of literature and to describe how you anticipate your research will begin to fill in some or all of those gaps.

The conclusion reiterates the importance and significance of your research proposal, and provides a brief summary of the entire proposed study. Essentially, this section should only be one or two paragraphs in length. Here is a potential outline for your conclusion:

Discuss why the study should be done. Specifically discuss how you expect your study will advance existing knowledge and how your study is unique.

Explain the specific purpose of the study and the research questions that the study will answer.

Explain why the research design and methods chosen for this study are appropriate, and why other designs and methods were not chosen.

State the potential implications you expect to emerge from your proposed study,

Provide a sense of how your study fits within the broader scholarship currently in existence, related to the research problem.

Citations and references

As with any scholarly research paper, you must cite the sources you used in composing your research proposal. In a research proposal, this can take two forms: a reference list or a bibliography. A reference list lists the literature you referenced in the body of your research proposal. All references in the reference list must appear in the body of the research proposal. Remember, it is not acceptable to say “as cited in …” As a researcher you must always go to the original source and check it for yourself. Many errors are made in referencing, even by top researchers, and so it is important not to perpetuate an error made by someone else. While this can be time consuming, it is the proper way to undertake a literature review.

In contrast, a bibliography , is a list of everything you used or cited in your research proposal, with additional citations to any key sources relevant to understanding the research problem. In other words, sources cited in your bibliography may not necessarily appear in the body of your research proposal. Make sure you check with your instructor to see which of the two you are expected to produce.

Overall, your list of citations should be a testament to the fact that you have done a sufficient level of preliminary research to ensure that your project will complement, but not duplicate, previous research efforts. For social sciences, the reference list or bibliography should be prepared in American Psychological Association (APA) referencing format. Usually, the reference list (or bibliography) is not included in the word count of the research proposal. Again, make sure you check with your instructor to confirm.

Research Methods for the Social Sciences: An Introduction by Valerie Sheppard is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

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How to Write an APA Methods Section | With Examples

Published on February 5, 2021 by Pritha Bhandari . Revised on June 22, 2023.

The methods section of an APA style paper is where you report in detail how you performed your study. Research papers in the social and natural sciences often follow APA style. This article focuses on reporting quantitative research methods .

In your APA methods section, you should report enough information to understand and replicate your study, including detailed information on the sample , measures, and procedures used.

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Table of contents

Structuring an apa methods section.

Participants

Example of an APA methods section

Other interesting articles, frequently asked questions about writing an apa methods section.

The main heading of “Methods” should be centered, boldfaced, and capitalized. Subheadings within this section are left-aligned, boldfaced, and in title case. You can also add lower level headings within these subsections, as long as they follow APA heading styles .

To structure your methods section, you can use the subheadings of “Participants,” “Materials,” and “Procedures.” These headings are not mandatory—aim to organize your methods section using subheadings that make sense for your specific study.

Note that not all of these topics will necessarily be relevant for your study. For example, if you didn’t need to consider outlier removal or ways of assigning participants to different conditions, you don’t have to report these steps.

The APA also provides specific reporting guidelines for different types of research design. These tell you exactly what you need to report for longitudinal designs , replication studies, experimental designs , and so on. If your study uses a combination design, consult APA guidelines for mixed methods studies.

Detailed descriptions of procedures that don’t fit into your main text can be placed in supplemental materials (for example, the exact instructions and tasks given to participants, the full analytical strategy including software code, or additional figures and tables).

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what to include in research proposal methodology

Begin the methods section by reporting sample characteristics, sampling procedures, and the sample size.

Participant or subject characteristics

When discussing people who participate in research, descriptive terms like “participants,” “subjects” and “respondents” can be used. For non-human animal research, “subjects” is more appropriate.

Specify all relevant demographic characteristics of your participants. This may include their age, sex, ethnic or racial group, gender identity, education level, and socioeconomic status. Depending on your study topic, other characteristics like educational or immigration status or language preference may also be relevant.

Be sure to report these characteristics as precisely as possible. This helps the reader understand how far your results may be generalized to other people.

The APA guidelines emphasize writing about participants using bias-free language , so it’s necessary to use inclusive and appropriate terms.

Sampling procedures

Outline how the participants were selected and all inclusion and exclusion criteria applied. Appropriately identify the sampling procedure used. For example, you should only label a sample as random  if you had access to every member of the relevant population.

Of all the people invited to participate in your study, note the percentage that actually did (if you have this data). Additionally, report whether participants were self-selected, either by themselves or by their institutions (e.g., schools may submit student data for research purposes).

Identify any compensation (e.g., course credits or money) that was provided to participants, and mention any institutional review board approvals and ethical standards followed.

Sample size and power

Detail the sample size (per condition) and statistical power that you hoped to achieve, as well as any analyses you performed to determine these numbers.

It’s important to show that your study had enough statistical power to find effects if there were any to be found.

Additionally, state whether your final sample differed from the intended sample. Your interpretations of the study outcomes should be based only on your final sample rather than your intended sample.

Write up the tools and techniques that you used to measure relevant variables. Be as thorough as possible for a complete picture of your techniques.

Primary and secondary measures

Define the primary and secondary outcome measures that will help you answer your primary and secondary research questions.

Specify all instruments used in gathering these measurements and the construct that they measure. These instruments may include hardware, software, or tests, scales, and inventories.

  • To cite hardware, indicate the model number and manufacturer.
  • To cite common software (e.g., Qualtrics), state the full name along with the version number or the website URL .
  • To cite tests, scales or inventories, reference its manual or the article it was published in. It’s also helpful to state the number of items and provide one or two example items.

Make sure to report the settings of (e.g., screen resolution) any specialized apparatus used.

For each instrument used, report measures of the following:

  • Reliability : how consistently the method measures something, in terms of internal consistency or test-retest reliability.
  • Validity : how precisely the method measures something, in terms of construct validity  or criterion validity .

Giving an example item or two for tests, questionnaires , and interviews is also helpful.

Describe any covariates—these are any additional variables that may explain or predict the outcomes.

Quality of measurements

Review all methods you used to assure the quality of your measurements.

These may include:

  • training researchers to collect data reliably,
  • using multiple people to assess (e.g., observe or code) the data,
  • translation and back-translation of research materials,
  • using pilot studies to test your materials on unrelated samples.

For data that’s subjectively coded (for example, classifying open-ended responses), report interrater reliability scores. This tells the reader how similarly each response was rated by multiple raters.

Report all of the procedures applied for administering the study, processing the data, and for planned data analyses.

Data collection methods and research design

Data collection methods refers to the general mode of the instruments: surveys, interviews, observations, focus groups, neuroimaging, cognitive tests, and so on. Summarize exactly how you collected the necessary data.

Describe all procedures you applied in administering surveys, tests, physical recordings, or imaging devices, with enough detail so that someone else can replicate your techniques. If your procedures are very complicated and require long descriptions (e.g., in neuroimaging studies), place these details in supplementary materials.

To report research design, note your overall framework for data collection and analysis. State whether you used an experimental, quasi-experimental, descriptive (observational), correlational, and/or longitudinal design. Also note whether a between-subjects or a within-subjects design was used.

For multi-group studies, report the following design and procedural details as well:

  • how participants were assigned to different conditions (e.g., randomization),
  • instructions given to the participants in each group,
  • interventions for each group,
  • the setting and length of each session(s).

Describe whether any masking was used to hide the condition assignment (e.g., placebo or medication condition) from participants or research administrators. Using masking in a multi-group study ensures internal validity by reducing research bias . Explain how this masking was applied and whether its effectiveness was assessed.

Participants were randomly assigned to a control or experimental condition. The survey was administered using Qualtrics (https://www.qualtrics.com). To begin, all participants were given the AAI and a demographics questionnaire to complete, followed by an unrelated filler task. In the control condition , participants completed a short general knowledge test immediately after the filler task. In the experimental condition, participants were asked to visualize themselves taking the test for 3 minutes before they actually did. For more details on the exact instructions and tasks given, see supplementary materials.

Data diagnostics

Outline all steps taken to scrutinize or process the data after collection.

This includes the following:

  • Procedures for identifying and removing outliers
  • Data transformations to normalize distributions
  • Compensation strategies for overcoming missing values

To ensure high validity, you should provide enough detail for your reader to understand how and why you processed or transformed your raw data in these specific ways.

Analytic strategies

The methods section is also where you describe your statistical analysis procedures, but not their outcomes. Their outcomes are reported in the results section.

These procedures should be stated for all primary, secondary, and exploratory hypotheses. While primary and secondary hypotheses are based on a theoretical framework or past studies, exploratory hypotheses are guided by the data you’ve just collected.

This annotated example reports methods for a descriptive correlational survey on the relationship between religiosity and trust in science in the US. Hover over each part for explanation of what is included.

The sample included 879 adults aged between 18 and 28. More than half of the participants were women (56%), and all participants had completed at least 12 years of education. Ethics approval was obtained from the university board before recruitment began. Participants were recruited online through Amazon Mechanical Turk (MTurk; www.mturk.com). We selected for a geographically diverse sample within the Midwest of the US through an initial screening survey. Participants were paid USD $5 upon completion of the study.

A sample size of at least 783 was deemed necessary for detecting a correlation coefficient of ±.1, with a power level of 80% and a significance level of .05, using a sample size calculator (www.sample-size.net/correlation-sample-size/).

The primary outcome measures were the levels of religiosity and trust in science. Religiosity refers to involvement and belief in religious traditions, while trust in science represents confidence in scientists and scientific research outcomes. The secondary outcome measures were gender and parental education levels of participants and whether these characteristics predicted religiosity levels.

Religiosity

Religiosity was measured using the Centrality of Religiosity scale (Huber, 2003). The Likert scale is made up of 15 questions with five subscales of ideology, experience, intellect, public practice, and private practice. An example item is “How often do you experience situations in which you have the feeling that God or something divine intervenes in your life?” Participants were asked to indicate frequency of occurrence by selecting a response ranging from 1 (very often) to 5 (never). The internal consistency of the instrument is .83 (Huber & Huber, 2012).

Trust in Science

Trust in science was assessed using the General Trust in Science index (McCright, Dentzman, Charters & Dietz, 2013). Four Likert scale items were assessed on a scale from 1 (completely distrust) to 5 (completely trust). An example question asks “How much do you distrust or trust scientists to create knowledge that is unbiased and accurate?” Internal consistency was .8.

Potential participants were invited to participate in the survey online using Qualtrics (www.qualtrics.com). The survey consisted of multiple choice questions regarding demographic characteristics, the Centrality of Religiosity scale, an unrelated filler anagram task, and finally the General Trust in Science index. The filler task was included to avoid priming or demand characteristics, and an attention check was embedded within the religiosity scale. For full instructions and details of tasks, see supplementary materials.

For this correlational study , we assessed our primary hypothesis of a relationship between religiosity and trust in science using Pearson moment correlation coefficient. The statistical significance of the correlation coefficient was assessed using a t test. To test our secondary hypothesis of parental education levels and gender as predictors of religiosity, multiple linear regression analysis was used.

If you want to know more about statistics , methodology , or research bias , make sure to check out some of our other articles with explanations and examples.

  • Normal distribution
  • Measures of central tendency
  • Chi square tests
  • Confidence interval
  • Quartiles & Quantiles

Methodology

  • Cluster sampling
  • Stratified sampling
  • Thematic analysis
  • Cohort study
  • Peer review
  • Ethnography

Research bias

  • Implicit bias
  • Cognitive bias
  • Conformity bias
  • Hawthorne effect
  • Availability heuristic
  • Attrition bias
  • Social desirability bias

In your APA methods section , you should report detailed information on the participants, materials, and procedures used.

  • Describe all relevant participant or subject characteristics, the sampling procedures used and the sample size and power .
  • Define all primary and secondary measures and discuss the quality of measurements.
  • Specify the data collection methods, the research design and data analysis strategy, including any steps taken to transform the data and statistical analyses.

You should report methods using the past tense , even if you haven’t completed your study at the time of writing. That’s because the methods section is intended to describe completed actions or research.

In a scientific paper, the methodology always comes after the introduction and before the results , discussion and conclusion . The same basic structure also applies to a thesis, dissertation , or research proposal .

Depending on the length and type of document, you might also include a literature review or theoretical framework before the methodology.

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Thesis, major paper, and major project proposals

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  • Introductory section
  • Literature review

Methodology

  • Schedule/work plan
  • Other potential elements
  • Proposal references
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what to include in research proposal methodology

The methodology section can include (but isn't limited to):

  • A description of the research design and methods
  • A description of data-gathering instruments
  • Methods of data collection
  • Ethical considerations
  • Analysis strategies and techniques
  • Potential participants
  • Rationale for your choice of methodological choices
  • How the methodology is appropriate for the organization or participants
  • The advantages and disadvantages of the methodology
  • References to scholarly literature that support the chosen research design and methods

If you are unsure if including the methodology is required in your thesis, major project, or research paper proposal, please consult with your instructor or advisor.

This information regarding the methodology section of a proposal was gathered from RRU thesis and major project handbooks, current in 2020, from programs in the Faculty of Social and Applied Sciences, the Faculty of Management, and the College of Interdisciplinary Studies. If the details here differ from the information provided in the handbook for your project, please follow the handbook's directions.

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  • In SAGE Research Methods Project Planner ; access via this link requires a RRU username and password.

Data Collection

How Do I Write About Theory?

  • In SAGE Research Methods: Writing Up ; look for the How Do I Write About Theory? drop down option. Access via this link requires a RRU username and password.

How Do I Write My Methodology Section?

  • In SAGE Research Methods: Writing Up ; look for the How Do I Write My Methodology Section? drop down option. Access via this link requires a RRU username and password.

Research Ethics

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  • Research Process

Choosing the Right Research Methodology: A Guide for Researchers

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Table of Contents

Choosing an optimal research methodology is crucial for the success of any research project. The methodology you select will determine the type of data you collect, how you collect it, and how you analyse it. Understanding the different types of research methods available along with their strengths and weaknesses, is thus imperative to make an informed decision.

Understanding different research methods:

There are several research methods available depending on the type of study you are conducting, i.e., whether it is laboratory-based, clinical, epidemiological, or survey based . Some common methodologies include qualitative research, quantitative research, experimental research, survey-based research, and action research. Each method can be opted for and modified, depending on the type of research hypotheses and objectives.

Qualitative vs quantitative research:

When deciding on a research methodology, one of the key factors to consider is whether your research will be qualitative or quantitative. Qualitative research is used to understand people’s experiences, concepts, thoughts, or behaviours . Quantitative research, on the contrary, deals with numbers, graphs, and charts, and is used to test or confirm hypotheses, assumptions, and theories. 

Qualitative research methodology:

Qualitative research is often used to examine issues that are not well understood, and to gather additional insights on these topics. Qualitative research methods include open-ended survey questions, observations of behaviours described through words, and reviews of literature that has explored similar theories and ideas. These methods are used to understand how language is used in real-world situations, identify common themes or overarching ideas, and describe and interpret various texts. Data analysis for qualitative research typically includes discourse analysis, thematic analysis, and textual analysis. 

Quantitative research methodology:

The goal of quantitative research is to test hypotheses, confirm assumptions and theories, and determine cause-and-effect relationships. Quantitative research methods include experiments, close-ended survey questions, and countable and numbered observations. Data analysis for quantitative research relies heavily on statistical methods.

Analysing qualitative vs quantitative data:

The methods used for data analysis also differ for qualitative and quantitative research. As mentioned earlier, quantitative data is generally analysed using statistical methods and does not leave much room for speculation. It is more structured and follows a predetermined plan. In quantitative research, the researcher starts with a hypothesis and uses statistical methods to test it. Contrarily, methods used for qualitative data analysis can identify patterns and themes within the data, rather than provide statistical measures of the data. It is an iterative process, where the researcher goes back and forth trying to gauge the larger implications of the data through different perspectives and revising the analysis if required.

When to use qualitative vs quantitative research:

The choice between qualitative and quantitative research will depend on the gap that the research project aims to address, and specific objectives of the study. If the goal is to establish facts about a subject or topic, quantitative research is an appropriate choice. However, if the goal is to understand people’s experiences or perspectives, qualitative research may be more suitable. 

Conclusion:

In conclusion, an understanding of the different research methods available, their applicability, advantages, and disadvantages is essential for making an informed decision on the best methodology for your project. If you need any additional guidance on which research methodology to opt for, you can head over to Elsevier Author Services (EAS). EAS experts will guide you throughout the process and help you choose the perfect methodology for your research goals.

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Research Method

Home » Research Methodology – Types, Examples and writing Guide

Research Methodology – Types, Examples and writing Guide

Table of Contents

Research Methodology

Research Methodology

Definition:

Research Methodology refers to the systematic and scientific approach used to conduct research, investigate problems, and gather data and information for a specific purpose. It involves the techniques and procedures used to identify, collect , analyze , and interpret data to answer research questions or solve research problems . Moreover, They are philosophical and theoretical frameworks that guide the research process.

Structure of Research Methodology

Research methodology formats can vary depending on the specific requirements of the research project, but the following is a basic example of a structure for a research methodology section:

I. Introduction

  • Provide an overview of the research problem and the need for a research methodology section
  • Outline the main research questions and objectives

II. Research Design

  • Explain the research design chosen and why it is appropriate for the research question(s) and objectives
  • Discuss any alternative research designs considered and why they were not chosen
  • Describe the research setting and participants (if applicable)

III. Data Collection Methods

  • Describe the methods used to collect data (e.g., surveys, interviews, observations)
  • Explain how the data collection methods were chosen and why they are appropriate for the research question(s) and objectives
  • Detail any procedures or instruments used for data collection

IV. Data Analysis Methods

  • Describe the methods used to analyze the data (e.g., statistical analysis, content analysis )
  • Explain how the data analysis methods were chosen and why they are appropriate for the research question(s) and objectives
  • Detail any procedures or software used for data analysis

V. Ethical Considerations

  • Discuss any ethical issues that may arise from the research and how they were addressed
  • Explain how informed consent was obtained (if applicable)
  • Detail any measures taken to ensure confidentiality and anonymity

VI. Limitations

  • Identify any potential limitations of the research methodology and how they may impact the results and conclusions

VII. Conclusion

  • Summarize the key aspects of the research methodology section
  • Explain how the research methodology addresses the research question(s) and objectives

Research Methodology Types

Types of Research Methodology are as follows:

Quantitative Research Methodology

This is a research methodology that involves the collection and analysis of numerical data using statistical methods. This type of research is often used to study cause-and-effect relationships and to make predictions.

Qualitative Research Methodology

This is a research methodology that involves the collection and analysis of non-numerical data such as words, images, and observations. This type of research is often used to explore complex phenomena, to gain an in-depth understanding of a particular topic, and to generate hypotheses.

Mixed-Methods Research Methodology

This is a research methodology that combines elements of both quantitative and qualitative research. This approach can be particularly useful for studies that aim to explore complex phenomena and to provide a more comprehensive understanding of a particular topic.

Case Study Research Methodology

This is a research methodology that involves in-depth examination of a single case or a small number of cases. Case studies are often used in psychology, sociology, and anthropology to gain a detailed understanding of a particular individual or group.

Action Research Methodology

This is a research methodology that involves a collaborative process between researchers and practitioners to identify and solve real-world problems. Action research is often used in education, healthcare, and social work.

Experimental Research Methodology

This is a research methodology that involves the manipulation of one or more independent variables to observe their effects on a dependent variable. Experimental research is often used to study cause-and-effect relationships and to make predictions.

Survey Research Methodology

This is a research methodology that involves the collection of data from a sample of individuals using questionnaires or interviews. Survey research is often used to study attitudes, opinions, and behaviors.

Grounded Theory Research Methodology

This is a research methodology that involves the development of theories based on the data collected during the research process. Grounded theory is often used in sociology and anthropology to generate theories about social phenomena.

Research Methodology Example

An Example of Research Methodology could be the following:

Research Methodology for Investigating the Effectiveness of Cognitive Behavioral Therapy in Reducing Symptoms of Depression in Adults

Introduction:

The aim of this research is to investigate the effectiveness of cognitive-behavioral therapy (CBT) in reducing symptoms of depression in adults. To achieve this objective, a randomized controlled trial (RCT) will be conducted using a mixed-methods approach.

Research Design:

The study will follow a pre-test and post-test design with two groups: an experimental group receiving CBT and a control group receiving no intervention. The study will also include a qualitative component, in which semi-structured interviews will be conducted with a subset of participants to explore their experiences of receiving CBT.

Participants:

Participants will be recruited from community mental health clinics in the local area. The sample will consist of 100 adults aged 18-65 years old who meet the diagnostic criteria for major depressive disorder. Participants will be randomly assigned to either the experimental group or the control group.

Intervention :

The experimental group will receive 12 weekly sessions of CBT, each lasting 60 minutes. The intervention will be delivered by licensed mental health professionals who have been trained in CBT. The control group will receive no intervention during the study period.

Data Collection:

Quantitative data will be collected through the use of standardized measures such as the Beck Depression Inventory-II (BDI-II) and the Generalized Anxiety Disorder-7 (GAD-7). Data will be collected at baseline, immediately after the intervention, and at a 3-month follow-up. Qualitative data will be collected through semi-structured interviews with a subset of participants from the experimental group. The interviews will be conducted at the end of the intervention period, and will explore participants’ experiences of receiving CBT.

Data Analysis:

Quantitative data will be analyzed using descriptive statistics, t-tests, and mixed-model analyses of variance (ANOVA) to assess the effectiveness of the intervention. Qualitative data will be analyzed using thematic analysis to identify common themes and patterns in participants’ experiences of receiving CBT.

Ethical Considerations:

This study will comply with ethical guidelines for research involving human subjects. Participants will provide informed consent before participating in the study, and their privacy and confidentiality will be protected throughout the study. Any adverse events or reactions will be reported and managed appropriately.

Data Management:

All data collected will be kept confidential and stored securely using password-protected databases. Identifying information will be removed from qualitative data transcripts to ensure participants’ anonymity.

Limitations:

One potential limitation of this study is that it only focuses on one type of psychotherapy, CBT, and may not generalize to other types of therapy or interventions. Another limitation is that the study will only include participants from community mental health clinics, which may not be representative of the general population.

Conclusion:

This research aims to investigate the effectiveness of CBT in reducing symptoms of depression in adults. By using a randomized controlled trial and a mixed-methods approach, the study will provide valuable insights into the mechanisms underlying the relationship between CBT and depression. The results of this study will have important implications for the development of effective treatments for depression in clinical settings.

How to Write Research Methodology

Writing a research methodology involves explaining the methods and techniques you used to conduct research, collect data, and analyze results. It’s an essential section of any research paper or thesis, as it helps readers understand the validity and reliability of your findings. Here are the steps to write a research methodology:

  • Start by explaining your research question: Begin the methodology section by restating your research question and explaining why it’s important. This helps readers understand the purpose of your research and the rationale behind your methods.
  • Describe your research design: Explain the overall approach you used to conduct research. This could be a qualitative or quantitative research design, experimental or non-experimental, case study or survey, etc. Discuss the advantages and limitations of the chosen design.
  • Discuss your sample: Describe the participants or subjects you included in your study. Include details such as their demographics, sampling method, sample size, and any exclusion criteria used.
  • Describe your data collection methods : Explain how you collected data from your participants. This could include surveys, interviews, observations, questionnaires, or experiments. Include details on how you obtained informed consent, how you administered the tools, and how you minimized the risk of bias.
  • Explain your data analysis techniques: Describe the methods you used to analyze the data you collected. This could include statistical analysis, content analysis, thematic analysis, or discourse analysis. Explain how you dealt with missing data, outliers, and any other issues that arose during the analysis.
  • Discuss the validity and reliability of your research : Explain how you ensured the validity and reliability of your study. This could include measures such as triangulation, member checking, peer review, or inter-coder reliability.
  • Acknowledge any limitations of your research: Discuss any limitations of your study, including any potential threats to validity or generalizability. This helps readers understand the scope of your findings and how they might apply to other contexts.
  • Provide a summary: End the methodology section by summarizing the methods and techniques you used to conduct your research. This provides a clear overview of your research methodology and helps readers understand the process you followed to arrive at your findings.

When to Write Research Methodology

Research methodology is typically written after the research proposal has been approved and before the actual research is conducted. It should be written prior to data collection and analysis, as it provides a clear roadmap for the research project.

The research methodology is an important section of any research paper or thesis, as it describes the methods and procedures that will be used to conduct the research. It should include details about the research design, data collection methods, data analysis techniques, and any ethical considerations.

The methodology should be written in a clear and concise manner, and it should be based on established research practices and standards. It is important to provide enough detail so that the reader can understand how the research was conducted and evaluate the validity of the results.

Applications of Research Methodology

Here are some of the applications of research methodology:

  • To identify the research problem: Research methodology is used to identify the research problem, which is the first step in conducting any research.
  • To design the research: Research methodology helps in designing the research by selecting the appropriate research method, research design, and sampling technique.
  • To collect data: Research methodology provides a systematic approach to collect data from primary and secondary sources.
  • To analyze data: Research methodology helps in analyzing the collected data using various statistical and non-statistical techniques.
  • To test hypotheses: Research methodology provides a framework for testing hypotheses and drawing conclusions based on the analysis of data.
  • To generalize findings: Research methodology helps in generalizing the findings of the research to the target population.
  • To develop theories : Research methodology is used to develop new theories and modify existing theories based on the findings of the research.
  • To evaluate programs and policies : Research methodology is used to evaluate the effectiveness of programs and policies by collecting data and analyzing it.
  • To improve decision-making: Research methodology helps in making informed decisions by providing reliable and valid data.

Purpose of Research Methodology

Research methodology serves several important purposes, including:

  • To guide the research process: Research methodology provides a systematic framework for conducting research. It helps researchers to plan their research, define their research questions, and select appropriate methods and techniques for collecting and analyzing data.
  • To ensure research quality: Research methodology helps researchers to ensure that their research is rigorous, reliable, and valid. It provides guidelines for minimizing bias and error in data collection and analysis, and for ensuring that research findings are accurate and trustworthy.
  • To replicate research: Research methodology provides a clear and detailed account of the research process, making it possible for other researchers to replicate the study and verify its findings.
  • To advance knowledge: Research methodology enables researchers to generate new knowledge and to contribute to the body of knowledge in their field. It provides a means for testing hypotheses, exploring new ideas, and discovering new insights.
  • To inform decision-making: Research methodology provides evidence-based information that can inform policy and decision-making in a variety of fields, including medicine, public health, education, and business.

Advantages of Research Methodology

Research methodology has several advantages that make it a valuable tool for conducting research in various fields. Here are some of the key advantages of research methodology:

  • Systematic and structured approach : Research methodology provides a systematic and structured approach to conducting research, which ensures that the research is conducted in a rigorous and comprehensive manner.
  • Objectivity : Research methodology aims to ensure objectivity in the research process, which means that the research findings are based on evidence and not influenced by personal bias or subjective opinions.
  • Replicability : Research methodology ensures that research can be replicated by other researchers, which is essential for validating research findings and ensuring their accuracy.
  • Reliability : Research methodology aims to ensure that the research findings are reliable, which means that they are consistent and can be depended upon.
  • Validity : Research methodology ensures that the research findings are valid, which means that they accurately reflect the research question or hypothesis being tested.
  • Efficiency : Research methodology provides a structured and efficient way of conducting research, which helps to save time and resources.
  • Flexibility : Research methodology allows researchers to choose the most appropriate research methods and techniques based on the research question, data availability, and other relevant factors.
  • Scope for innovation: Research methodology provides scope for innovation and creativity in designing research studies and developing new research techniques.

Research Methodology Vs Research Methods

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What to include in a research proposal

You should check with each department to find out whether they provide a specific template for submission.

The word count for research proposals is typically 1,000-1,500 words for Arts programmes and around 2,500 words for Birmingham Law School programmes. Each subject area or department will have slightly different requirements for your research proposal, such as word length and the volume of literature review required. It is a good idea to contact the department before you apply. 

Typically, your research proposal should include the following information:

2. Research overview

3. research context.

A well-written introduction is an efficient way of getting your reader’s attention early on. This is your opportunity to answer the questions you considered when preparing your proposal: why is your research important? How does it fit into the existing strengths of the department? How will it add something new to the existing body of literature?

It is unlikely that you will be able to review all relevant literature at this stage, so you should explain the broad contextual background against which you will conduct your research. You should include a brief overview of the general area of study within which your proposed research falls, summarising the current state of knowledge and recent debates on the topic. This will allow you to demonstrate a familiarity with key texts in the relevant field as well as the ability to communicate clearly and concisely.

4. Research questions

The proposal should set out the central aims and key questions that will guide your research. Many research proposals are too broad, so make sure that your project is sufficiently narrow and feasible (i.e. something that is likely to be completed within the normal time frame for a PhD programme).

You might find it helpful to prioritise one or two main questions, from which you can then derive a number of secondary research questions. The proposal should also explain your intended approach to answering the questions: will your approach be empirical, doctrinal or theoretical, etc.?

5. Research methods

How will you achieve your research objectives? The proposal should present your research methodology, using specific examples to explain how you are going to conduct your research (e.g. techniques, sample size, target populations, equipment, data analysis, etc.).

Your methods may include visiting particular libraries or archives, field work or interviews. If your proposed research is library-based, you should explain where your key resources are located. If you plan to conduct field work or collect empirical data, you should provide details about this (e.g. if you plan interviews, who will you interview? How many interviews will you conduct? Will there be problems of access?). This section should also explain how you are going to analyse your research findings.

A discussion of the timescale for completing your research would also beneficial. You should provide a realistic time plan for completing your research degree study, showing a realistic appreciation of the need to plan your research and how long it is likely to take. It is important that you are not over-optimistic with time frames.

6. Significance of research

The proposal should demonstrate the originality of your intended research. You should therefore explain why your research is important (for example, by explaining how your research builds on and adds to the current state of knowledge in the field or by setting out reasons why it is timely to research your proposed topic) and providing details of any immediate applications, including further research that might be done to build on your findings.

Please refer to our top tips page for further details about originality.

7. References

  Read our top tips for writing a research proposal

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  • Review Article
  • Open access
  • Published: 31 August 2023

Infrared avalanche photodiodes from bulk to 2D materials

  • Piotr Martyniuk 1 , 2 ,
  • Peng Wang 2 ,
  • Antoni Rogalski   ORCID: orcid.org/0000-0002-4985-7297 1 ,
  • Ruiqi Jiang 2 ,
  • Fang Wang 2 &
  • Weida Hu   ORCID: orcid.org/0000-0001-5278-8969 2  

Light: Science & Applications volume  12 , Article number:  212 ( 2023 ) Cite this article

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  • Optical materials and structures
  • Optoelectronic devices and components

Avalanche photodiodes (APDs) have drawn huge interest in recent years and have been extensively used in a range of fields including the most important one—optical communication systems due to their time responses and high sensitivities. This article shows the evolution and the recent development of A III B V , A II B VI , and potential alternatives to formerly mentioned—“ third wave ” superlattices (SL) and two-dimensional (2D) materials infrared (IR) APDs. In the beginning, the APDs fundamental operating principle is demonstrated together with progress in architecture. It is shown that the APDs evolution has moved the device’s performance towards higher bandwidths, lower noise, and higher gain-bandwidth products. The material properties to reach both high gain and low excess noise for devices operating in different wavelength ranges were also considered showing the future progress and the research direction. More attention was paid to advances in A III B V APDs, such as AlInAsSb, which may be used in future optical communications, type-II superlattice (T2SLs, “Ga-based” and “Ga-free”), and 2D materials-based IR APDs. The latter—atomically thin 2D materials exhibit huge potential in APDs and could be considered as an alternative material to the well-known, sophisticated, and developed A III B V APD technologies to include single-photon detection mode. That is related to the fact that conventional bulk materials APDs’ performance is restricted by reasonably high dark currents. One approach to resolve that problem seems to be implementing low-dimensional materials and structures as the APDs’ active regions. The Schottky barrier and atomic level thicknesses lead to the 2D APD dark current significant suppression. What is more, APDs can operate within visible (VIS), near-infrared (NIR)/mid-wavelength infrared range (MWIR), with a responsivity ~80 A/W, external quantum efficiency ~24.8%, gain ~10 5 for MWIR [wavelength, λ  = 4 μm, temperature, T  = 10–180 K, Black Phosphorous (BP)/InSe APD]. It is believed that the 2D APD could prove themselves to be an alternative providing a viable method for device fabrication with simultaneous high-performance—sensitivity and low excess noise.

Introduction

The avalanche multiplication effect can be used to detect low-power optical signals and even single-photons due to the amplification mechanism within all main: near- (NIR), short- (SWIR), mid- (MWIR), and long wavelength infrared radiation (LWIR) ranges. An advanced laser radar and weapons systems implemented in long-range army and space applications must detect, recognize and track various targets under a diversity of atmospheric conditions including absorption by CO, CO 2 , and H 2 O vapor, which leads to significant signal attenuation in the optical system. That output signal suppression requires an extra amplifier along with a system to correctly detect the signal at the detector stage. The devices based on avalanche photodiodes (APDs) exhibiting high bandwidth ( BW ) and gain ( M )—high gain-bandwidth product ( GBW ) and low excess noise [ F(M) ] at the same time are well matched to detect suppressed optical signals, e.g., in the long-distance applications such as free-space optical communications (FSO), night vision, light detection, and ranging (LIDAR/LADAR), time of flight (ToF), intelligent robotic and finally in battlefield conditions (military applications). Therefore, improvement in GBW and F(M) reduction has been a key goal for APD’s progress. The methods to suppress the F(M) may be divided into three tactics. The initial approach could be to choose a material (to include “ third wave ” materials and their technologies) with advantageous multiplication properties. Next, the F(M) may be substantially limited by the reduction of the avalanche layer to use the non-local effect of the multiplication phenomena. The final method may be widely categorized as impact ionization engineering ( I 2 E ) exploiting properly constructed heterojunctions.

The APD materials’ selection is conditioned by the potential applications to include the most common: high-speed receivers, single-photon counters, and laser range finders 1 , 2 . In the field of fiber optic communication (FOC), InGaAs ternary alloy is much more expensive in terms of fabrication than Ge, but provides lower noise and higher time response. The Ge APDs are advised for detection systems where noise generated by the amplifier is high. The development of device technology with active regions built of the narrow gap semiconductors, such as HgCdTe and T2SLs (“ third wave ” material/technology) has contributed to the development of the new passive/active detection applications and capabilities. In active imagery systems, a laser source is implemented to the observed region, and reflected radiation is temporally examined. The output signal may be amplified in the APD itself, before going to the readout integrated circuit (ROIC). In addition, the grouping of dual-band capability and multiplication gain is another technology enabling dual-band detection for a wide temperature selection.

The APD could operate under the conditions where applied bias is higher than the infinite gain voltage meaning that the appearance of the single-photon causes an avalanche breakdown producing a high signal marking the presence of another photon (passive or active imaging). This mode of operation is referred to as a counting or single-photon avalanche detector (SPAD)—called a Geiger mode avalanche detector by Cova et al. pioneering paper 3 . The SPAD is more sensitive than a photomultiplier, however, when the avalanche process is initiated at infinite gain, additional photons detected during the pulse and circuit regeneration are discounted which makes SPAD more like a Geiger counter than a photomultiplier. SPADs build a variety of approaches to reach single-photon detection (SPD) mode and compete with superconducting nanowire single-photon detectors (SNSPDs). The main reason for this tendency is unquestionably the move to optical quantum information applications—quantum key distribution (QKD) putting severe requirements on detector parameters that move away from the performance of the well-developed typical APDs. Effective single-photon numeration, with a single-photon detection efficiency (SPDE) > 50%, was reached just for wavelengths shorter than <2 μm 4 . SNSPDs exhibit outstanding performance on a wide wavelength range, but their applications is restricted by cryogenic cooling requirements. In contrast, SPADs circumvent the SNSPDs’ fundamental restrictions by offering a reasonable option at ≤300 K mainly by A III B V material leader—InGaAs. Reaching the high performance in the MWIR exhibits potential in astronomy, LIDAR, dark matter research applications, and examination of chemistry and molecular dynamics, to include many absorption fingerprints for molecules: H 2 O, CO 2 , O 2 , O 3 , CH 4, and N 2 O 3 5 . Figure 1 illustrates the significance of these devices pointing to the technology roadmap development from typical bulk to low-dimensional APDs to include SPDs 6 , 7 , 8 .

figure 1

Methods, technologies, and applications roadmap for avalanche photon-sensing technologies starting from bulk to low-dimensional materials

The focal plane array (FPA) intended to operate in LWIR is advantageous because the number of photons in the 8–12 μm atmospheric transparency window is significant for reaching high detectivity and response time. In addition, astronomy applications need FPAs exhibiting high M and low F(M) , to detect low radiation flux from far located stars. The avalanche ionization in LWIR can be more simply reached in comparison with SWIR and MWIR devices. Even though a higher M may be reached under a given bias, the large dark current is an issue for LWIR APDs significantly impacting the device performance. Derelle et al. presented the n + /n − /p planar APD deposited by molecular beam epitaxy (MBE), exhibiting M  = 16 at −2.7 V and cut-off wavelength, λ c  ~ 9 μm at 80 K. Authors showed that the F(M) assessment in HgCdTe LWIR APDs is restricted to low M [ F(M)  = 1–1.25 at M  = 6] caused by tunneling currents influence 9 . Since the photocurrent to dark current ratio is low at high reverse voltage in LWIR it is difficult to estimate F(M) with high M 10 , 11 .

The member of the “ third wave ” group—two-dimensional (2D) layered materials and van der Waals (vdW) heterostructures can be also used to fabricate avalanche multiplication to include single-photon-counting technologies. Recently, the spectacular growth in the quantity of research papers related to the promising 2D photodetectors has been observed, however, those materials exhibit low absorption caused by their thin atomistical nature. To use those unique 2D materials properties for device design, the considerable latest attempts have been directed at combining with photonic structures (dielectric waveguides), plasmonic structures, or photonic crystals. That combination with photonic structures allowed to demonstrate single graphene layer with high absorption, modulators, detectors, and lasers 12 . Impact ionization leading to the carrier avalanche is a favorable approach to fabricating 2D photodetectors exhibiting high detection efficiency.

In comparison to standard bulk, the 2D materials exhibit numerous exceptional capabilities, such as mechanical flexibility, strong light-matter coupling, self-passivated surfaces, and gate-tunable Fermi-level providing flexibility in heterostructure design 13 , 14 . Those materials are characterized by different impact ionization coefficients versus carrier transport direction. The electric field needed for avalanche multiplication in out-of-plane transport is hundreds of kV/cm, while for in-plane close to tens of kV/cm is confirmed by measured results 15 . The 2D layered gapless graphene can detect radiation from ultraviolet (UV) to microwave making it an alternative for numerous photodetector designs operating in wide spectral ranges, however, its zero-bandgap characteristics limit the fabrication of photodetectors with high detectivity. Alternatively, 2D transition metal dichalcogenides (TMDs), thickness-dependent energy bandgap MoS 2 and WSe 2 , exhibit promising photodetection capabilities mainly in the visible (VIS) to NIR ranges to include impact ionization effect. In comparison to the graphene and TMDs, 2D black phosphorus (BP) exhibiting a direct energy bandgap within the range from 0.3 eV (bulk) to 2 eV (monolayer) proved to be a proper material candidate for APD technology 8 . The multiplication was also observed in 2D InSe for the VIS range. In addition, not only the conventional impact ionization effect but also the ballistic avalanche mechanism was observed in the 2D materials family. The effectiveness of the multiplication mechanism varies versus the material’s intrinsic capabilities. Consequently, the research of innovative materials characterized by the low electric field for avalanche multiplication is significant in reaching energy-effective devices. The avalanche multiplication mechanism in conventional materials is restricted by high bias which could be circumvented by 2D materials-based APDs 15 .

Taking the above into consideration this paper shows the current status and future development of IR-based APDs. It encompasses both bulk HgCdTe and A III B V based material systems including well-known “ third wave ” material family member—superlattices (SLs). In addition, the current progress in the new materials and architectures for high-performance IR APDs is presented to include innovative “ third wave ” 2D materials. In addition, the strategies to reach high-performance APDs are presented. The field related to the APD advances in telecommunications is generally omitted due to the excellent review papers published recently 16 , 17 .

Figure 2(a–c) presents the diagram of the multiplication effect in APD, where the internal gain is obtained through the avalanche mechanisms generated by the stochastic impact ionization process inherently accompanied by F(M) deterioration limiting GBW . This is because both carriers (electron and hole) may be multiplicated. The carriers are photogenerated in the low electric field active layer and, ideally, only the carriers exhibiting the utmost impact ionization probability are moved toward the high-electric field multiplication area.

figure 2

a Electron and hole multiplication mechanisms, schematic of multiplication mechanism for b k  = 0 ( α h  = 0) and c k  = 1 ( α e  =  α h ), where k  =  α h / α e  –  α e , α h represent electron and hole multiplication coefficients. d α e , α h ionization coefficients versus electric field for selected semiconductors used for APDs’ fabrication 26

The carrier’s ability to multiply is given by the α e (electrons) and α h (holes) ionization coefficients. Those parameters describe the multiplication probability per unit length meaning that ~1/ α e and ~1/ α h represent an average distance carrier moves before impact ionization occurs [see Fig. 2(a) ]. The electron and hole ionization coefficients, thus, k  =  α h / α e , are conditioned by the material properties like the carriers’ effective masses and scattering mechanisms. The electron and hole ionization coefficients rise versus voltage and decline versus temperature. The rise in voltage is driven by extra carrier velocity under an electric field, while the decrease versus temperature relates to the non-ionizing collisions with thermally excited atoms. However, there are reports about positive temperature variation of In 0.53 Ga 0.47 As impact ionization 18 . The ionization coefficients follow the Chynoweth model exhibiting exponential dependence on the electric field (for a given temperature):

where: E is an electric field in the multiplication area and a , b , c are measured constants.

The carriers’ ionization coefficient ratio, k  = α h /α e is considered an important parameter characterizing the APD’s performance. When holes do not multiplicate significantly (α h « α e , k → 0), the avalanche ionization is driven by electrons. As Fig. 2(b) depicts the avalanche process proceeds from left to right and ends after all electrons reach the n-type part of the depletion layer. When both carriers multiplicate ( k → 1), the holes are transported to the left creating electrons being moved to the right generating more holes transported to the left, in a feasibly infinite cycle. The impact ionization effect for k  = 1 is chain-like [see Fig. 2(c) ]. In contrast, for k  = 0, only one electron pass is required, taking less time to reach a similar gain level. That mechanism raises the detector’s gain meaning that the net number of the generated charges in the considered circuit per photocarrier pairs increases. That is a highly unwanted process to include the following reasons:

time-consuming—limits the detector’s BW ;

random—increases the detector’s noise;

unstable—leading to the avalanche breakdown.

It must be stressed that for materials exhibiting comparable multiplication coefficients and negligible “ dead space ” effect, although the breakdown prospect raises more slowly with voltage the breakdown process was found to be quick and jitter low. As the thickness of the multiplication area is scaled, the breakdown time and jitter decrease leading to time performance improvement which was confirmed for InP and Si SPADs. Moreover, an increase of the carrier’s velocities multiplicating in their tracks is believed to lower breakdown time and jitter 19 .

Figure 2(d) shows the carrier’s multiplication coefficients dependence on E (electric field) for selected materials used for the APDs’ fabrication. As can be seen, starting from E  ~ 10 5  V/cm, the ionization coefficients raise rapidly versus a small E gradient, but for fields E  < 10 5  V/cm carrier multiplication is insignificant for considered materials. For some materials to include: Si, GaAsSb, and InGaAs (where α e  >  α h ) electrons ionize more effectively than holes while for Ge, GaAs (where α h  >  α e ) holes multiplicate more efficiently than electrons.

Taking the above conditions into consideration, the APDs’ fabrication process requires materials allowing multiplication by either electrons or holes. When electrons exhibit a higher avalanche coefficient, the multiplication mechanism should be initiated by injecting the photogenerated electron at the p-type edge of the depletion layer. In that case, the material should exhibit as low as possible k -values. On the other hand, if holes launch the multiplication process, the photogenerated hole should be transported into the n-type edge of the depletion region assuming as high as possible k -values. The perfect single-carrier avalanche mechanism is reached when the following conditions are met:

k  =  α h / α e  = 0 ( α h « α e ) for electrons;

k  = ∞ ( α h » α e ) for holes.

The impact ionization factor k also affects the GBW . The time needed for the APD to reach a required gain level is termed by the avalanche build-up time or multiplication time being inversely proportional to the GBW .

Figure 3(a–c) show the InGaAs APDs design’s evolution. Initially, APD was designed as a p – n junction operating primarily in linear mode as shown in Fig. 3(a) 20 . Its operating bias was lower than multiplication breakdown voltage and the avalanche current scaled linearly to the light power. The limitation of the APD based on the p – n junction is that the depletion area containing the multiplication region is part of the absorption layer resulting in an electric field drop over both absorber and avalanche regions. Consequently, the APDs based on the p – n junction are characterized by high dark current (significant contribution of tunneling current is observed) and low gain. To remove this drawback, in 1979 Nishida et al. fabricated the detector with the n-InGaAsP absorption and P + -InP multiplication areas being separated by an extra n-InP layer (SAM) as presented in Fig. 3(b) 21 . Further evolution of the APD architecture occurred in the early 1990s by the implementation of isolated absorption, grading, charge, and multiplication structures (SAGCM) which allowed to suppress the tunneling current contribution [see Fig. 3(c) ] 22 , 23 . The band offset between the absorber, avalanche layers, and design of the charge/grading regions have to be considered as the key parameters of the SAGCM. An additional n-InP charge region was introduced into the SAM structure to modify the distribution of the electric field. Furthermore, the InGaAsP grading area was added to reduce the valence band discontinuities between the InP and InGaAs regions. This resulted in avalanche structures with the highest sensitivity (SAGCMs) currently used in the NIR band [see Fig. 3(c) ].

figure 3

a p – n device, b SAM device, and c SAGCM device with electric field distribution. F(M) dependence on M for the selected k  =  α h / α e in APDs when: d electrons and e holes dominate in the avalanche mechanism. The multiplication path length probability distribution functions in the: f local and g non-local field “ dead space ” models

A complete theory of the APD’s multiplication excess noise was proposed by McIntyre 24 , 25 . This theory is created on the local-field model according to which the carriers’ multiplication coefficients are in equilibrium. The APD’s noise per unit bandwidth can be given by the equation:

where: < M >—average avalanche gain, q —electric charge, I ph —photocurrent for gain, M  = 1, and F(M) —excess noise factor related to gain arising from the probabilistic character of the ionization effect.

According to the McIntyre theory, if the electrons initiate multiplication the F(M) may be calculated based on the following formula:

while for the holes starting the avalanche process, the equation assumes:

In terms of the simple p–n-based photodetectors under reverse voltage exhibiting no multiplication gain, < M > = 1, F(M)  = 1 and the shot noise given by equation \(\left\langle {I}_{n}^{2}\right\rangle =2q{I}_{{ph}}\) limits the detector’s performance. Assuming, that injected photocarriers exhibit the same gain M , F(M)  = 1 and the noise power may be given by the noise caused by accidental transport of photogenerated carriers, multiplied by M 2 . In contrast, the multiplication effect is inherently stochastic, meaning that the carriers exhibit different avalanche gains distributed with mean gain < M >. This is related to the extra noise source referred to as avalanche over-noise, being easily given by the F(M) in Eq. ( 2 ). Figure 3(d, e) presents the APD’s F(M) versus M for the selected k  =  α h / α e . If k  = 0 (pure electron injection) the F(M) maintains constant value versus gain, as presented in Fig. 3(d) , while in terms of the pure hole injection observed for k  > 50, F(M) stays constant versus M and changes for low k as presented in Fig. 3(e) .

As already mentioned, to reach a low excess noise factor, the carrier’s ionization coefficients must be as different in values as viable, and the multiplication effect has to be launched by carriers with higher ionization coefficients. Most A III B V semiconductors have an ionization factor within the range of 0.4 ≤ k  ≤ 2 26 .

The local field model correctly describes the multiplication process and excess noise when the avalanche layer is thick (>1 μm). Figure 3(f, g) presents the carriers’ ionization probability in the avalanche region. Ionization probability decreases exponentially versus distance from the injection region, however, with thinning the multiplication region to the submicron level, the local field theory does not justify the F(M) lowering 27 , 28 . To explain this device phenomenon, a non-local effect in the multiplication mechanism was proposed 29 , 30 . The multiplication process is non-local and carriers transported into the high-electric field area need a specific length, to reach the necessary energy to multiplicate 29 , 31 . That specific length where carriers are not multiplicated is called “ dead space ”, d . The “ dead space ” effect imposes the changes in the probability distribution function (PDF) of the multiplication effect as presented in Fig. 3(g) . For the thin multiplication region, the electric field must be higher than assumed to reach a specific impact ionization increase. When the “ dead space ” is considered, the PDF width is narrower causing the multiplication mechanism more deterministic.

Therefore, F(M) can be suppressed by thinning (scaling) the impact ionization layer. The “ dead space ” for both carriers could be roughly estimated by E th —ionization threshold energy depending on the material’s band structure and E (~ E th / qE ). The “ dead space ” contribution may be substantial leading to significant excess noise suppression due to a much narrower PDF than given by the local field theory. Consequently, an APD exhibiting low excess noise may be fabricated based on material exhibiting k  ~ 1 2 , 16 , 32 . The avalanche region length reduction is another advantage—it increases the frequency response.

The APDs GBW is derived from the time needed for the multiplication effect to decay or build up. The time constant, gain, and bandwidth are related to each other. The lower bandwidth the higher gain and the higher the time constant, however, it was Emmons who presented that the bandwidth limitation disappears when either electron or hole ionization coefficients assume α h  =  α e  = 0 33 . Assuming non-zero ionization coefficients ( α h  ≠ 0, α e  ≠ 0), the time dependence of the average electron-initiated gain may be estimated by the equation:

where: M o is the DC gain, τ is roughly the carrier transit time across the avalanche layer.

As is marked above, the most important APD performance could be given by:

excess noise factor [ F(M) ];

bandwidth ( BW );

gain ( M );

gain-bandwidth product ( GBW ).

Three approaches to designing and fabricating high-performance APDs could be distinguished to obtain low F(M) and high GBW :

semiconductor selection exhibiting proper impact carrier multiplication coefficients;

thinning the avalanche area to use the multiplication effect non-local field capability;

properly designed heterojunctions by impact ionization engineering ( I 2 E ).

The current bulk and type-II superlattice (T2SLs) materials suitable for high-performance APDs’ fabrication and their spectral ranges are gathered in Table 1 . In turn, Table 2 compares their general state-of-the-art to include cut-off wavelength ( λ c ), quantum efficiency ( QE ), gain ( M ), excess noise factor [ F(M) ], operating temperature ( T ), manufacturability, and limitations with technology readiness level (TRL) 34 .

A III B V infrared avalanche photodiodes

The semiconductor’s selection for APDs fabrication is conditioned by applications where the most common are fiber optic communications, high-speed receivers, single-photon counters, and laser range finders. Even though the IV-group semiconductor materials such as Si and Ge exhibit superior performance among APDs, Si and Ga-based APDs cannot operate in a 1.55 μm optical communication band due to their cut-off wavelength limitations. For this reason, the research efforts have been directed at InGaAs/InP APDs. Much current research on the APDs has been focused on the development of the new architecture and the materials substitutions/alternatives to lower dark current, to reach higher speed and lower excess noise maintaining optimal gain levels at the same time. Recently GeSn APDs have been introduced to circumvent the longer cut-off wavelength limitations 35 , 36 . The InAlAs or InP submicron multiplication areas with InGaAs absorption layers (InGaAs is reported to be lattice matched to InAlAs and InP) could be used to reach lower F(M) because of “ dead space ” effect. The InAlAs k  =  α h / α e is reported to be much higher than the InP k reached for low E . The InAlAs F(M) is much lower than in InP at a given gain due to the high InAlAs α h / α e ratio and the favorable InP “ dead space ” effect. Moreover, light with a wavelength, λ  > 1.4 μm called “ eye-safe ”, goes to the eye anterior potions eye (primarily the cornea) consequently not reaching the retina. Since Si does not absorb beyond > 1 μm, A III B V semiconductors offer the potential for longer wavelengths of LIDARs.

For high-speed telecommunication receivers, the APDs exhibiting short response time and high GBW are required. Time response and GBW are mainly restricted by the profile of the heterojunction between the active and avalanche regions and the doping distribution within the detector. Attempts to reach improvement in avalanche gain for InGaAs by rising the electric field are not feasible which is related to the tunneling effects resulting in high leakage currents. The low value of the electron effective mass causes a sharp increase in tunneling current for electric fields, E  > 150 kV/cm 37 , 38 . That drawback was circumvented by combining an InGaAs absorber layer operating with low E and a lattice-matched InP multiplication layer with a wider bandgap responsible for impact ionization. That architecture is an example of the previously mentioned SAM-APD design (isolated absorption and multiplication layers). The InGaAs/InP SAM-APD device structure, with a double-diffused floating guard ring, is presented in Fig. 4(a) , while the heterostructure energy band profile and electric field distribution are presented in detail in Fig. 4(b) . The radiation is absorbed in InGaAs active layer and photogenerated holes [exhibiting higher multiplication coefficient than electrons which guarantees low F(M) ] are transported to InP heterojunction, where the impact ionization occurs. That design allows for low surface current caused by the junction being located in the wide energy gap InP providing responsivity in the longer wavelength range by the low energy gap InGaAs active layer.

figure 4

a device structure, b energy band profile, and electric field under normal reverse bias condition. Al x In 1– x As y Sb 1– y based SACM APD: c detector’s design with the E distribution within the detector, d measured and theoretically simulated gain, dark current, photocurrent versus reverse voltage for 90 μm diameter device at room temperature 39 . InAs planar avalanche photodiode: e a schematic design diagram, f comparison of the gain reached by 1550 nm wavelength laser 132 , 133 . The M normalized dark current for 100 μm radius planar APD was presented for 200 K

InGaAs/InP heterojunction APDs are usually built of the 1–2 μm thick undoped active layer. The 0.1–0.3 μm thick InGaAsP grading and 1–2 μm thick multiplication regions are doped up to the level 1 × 10 16  cm −3 . The p + -layer is thin and doped up to the level of 10 17 –10 18  cm −3 . The junction is typically produced by Zn p + -type diffusion into the InP avalanche region and Cd diffusion (or implantation) for the guard ring into the top InP layer through the SiO 2 mask.

It must be stressed that the valence band offset at the InGaAs/InP junction accumulates holes in the valence band which deteriorates the device’s response time. That valence band discontinuity is reduced by grading the bandgap of the quaternary InGaAsP layer grown between the InP and InGaAs regions. That improved architecture is referred to as the separate, absorption, graded, multiplication avalanche photodiode (SAGM).

The Al x In 1– x As y Sb 1– y separate absorption, charge, and multiplication (SACM) APD is presented in Fig. 4(c) . The device architecture includes (order from the very top): GaSb contact layer, p-type Al 0.7 In 0.3 As 0.3 Sb 0.7 (100 nm thick, 2 × 10 18  cm −3 ) blocking region, Al x In 1– x As y Sb 1– y within the region x  = 0.4–0.7 grading region, p − -type Al 0.4 In 0.6 As 0.4 Sb 0.4 1000 nm thick active region, 150 nm thick, p + -type Al 0.7 In 0.3 As 0.3 Sb 0.7 charge region (1.25 × 10 17  cm −3 ), 1000 nm thick p − -type Al 0.4 In 0.6 As 0.4 Sb 0.4 multiplication region, and finally n-type GaSb contact region [(1–9) × 10 17  cm −3 ]. Lastly, N 2 /Cl 2 inductive coupled plasma (ICP) and typical photolithography with bromine methanol and SU-8 treatment to reduce leakage current were used to define circular mesas.

Under the strong reverse bias, the high E within the multiplication layer enables the avalanche effect, and photogenerated electrons drift is realized by a small electric field suppressed by the charge region in the absorber layer. Figure 4(d) shows 25 μm radius Al x In 1– x As y Sb 1– y SACM APD performance. The dark current at 95% breakdown voltage assumes ~120 nA, being roughly ~100× lower than the current for APDs based on Ge on Si and like AlInAs/InGaAs APDs 39 . The experimental M  ~ 50 values were confirmed by the Monte Carlo simulations.

In the last decade, a new breakthrough in the development of InAs APDs has been reached 40 . Their high potential is conditioned by the low production expenses related to the easily available A III B V fabrication foundries and the relatively low price of the 6” native substrates, as well as the operation using thermoelectric cooling. The historical problem with the surface leakage of InAs photodiodes is gradually reduced by elaborating wet chemical etching recipes like the solutions of phosphoric and sulfuric acid-based etchants 41 .

Both mesa and planar InAs APDs were fabricated. For mesa p-i-n structures, the M normalized dark current density ( J Dark ) at the level of ~5 × 10 −6 A/cm 2 for LN 2 temperature (77 K) has been published 42 . The onset of BTB tunneling at moderately low E requires a thicker multiplication region to achieve high multiplication gain exacerbating passivation difficulties. To resolve that issue, planar structures as shown in Fig. 4(e) have been developed and described in detail in ref. 40 . To form a p – n junction, Beryllium (Be) implantation at low energy was used.

Table 3 presents the APDs based on Si, Ge, and InGaAs parameters/performance. Data is shown for comparison reasons among materials used for APDs’ fabrication.

Progress in materials’ properties and advanced detector structures have increased the APDs performance for fiber optic communication systems over the past decade 16 , 17 , 43 , 44 . These include the introduction of the continuous or grading bandgap for absorption/avalanche layers to limit carrier trapping and insertion of the electric-field control layers. Advanced APDs structures require the multiplication region thickness to be shrinked to reach fast response times. The local McIntyre theory does not properly justify the excess noise characteristics for the devices with thin multiplication regions. The InP APD with the 0.25 μm-thick multiplication region reaches the excess noise performance scaling with 1/ k  ~ 0.25 for the hole-initiated avalanche process (h-APD), however, according to the McIntyre model, the multiplication factor is reported at the level of ~0.7. The significant reduction in excess noise can be reached by the “ dead space ” effect in the thin multiplication layers. Additional improvements in the detector’s excess noise may be reached by the implementation of the InAlAs/InAlAsSb (instead of InP) being lattice-matched to InGaAs and InP as the multiplying layer. The InAlAs/InAlAsSb α h / α e was estimated to be much higher than the InP α h / α e ratio at low E . The InAlAs F(M) at a given M is much smaller than in InP being related to the high InAlAs α h / α e ratio and the favorable “ dead space ” effect in InP.

Figure 5(a) presents the F(M) versus M for selected material systems. The solid lines present the F(M) for k  = 0–1 values simulated by the local field theory 24 . In general, F(M) should increase versus k . Typical excess noises are shown by shaded regions 37 . The k  =  α h / α e values for the best commercially available Si APDs stay within the range 0.01–0.06. InP and InAlAs commonly implemented as avalanche regions of the APDs for telecommunication applications assume higher k -values:

InP within the range k  = 0.4–0.5;

InAlAs within the range k  = 0.2–0.3 44 .

figure 5

a Si, AlInAs, GaAs, Ge, InP [the solid lines present the F(M) for k within the range 0–1 (increment 0.1) calculated by the local field model 24 , typical F(M) are shown by shaded regions 37 and b selected materials: 3.5 μm thick intrinsic InAs APDs (50 μm and 100 μm radius), 4.2 μm cut-off wavelengths HgCdTe and 2.2 μm InAlAs APDs 134

Lately, two quaternary A III B V bulk compound semiconductors, Al x In 1– x As y Sb 1– y to GaSb and Al x Ga 1– x As y Sb 1– y lattice-matched to InP were reported to reach excess noise comparable to Si 17 . The Al x Ga 1– x As y Sb 1– y APDs within the range of Al chemical composition, x  = 0.5–0.7 exhibit k -values at the level of 0.01. This behavior is explained by the significant domination of electron impact multiplication in comparison to the holes, which is related to the Sb contribution/content. It is suggested that Sb-content increases photon scattering rates and increases effective hole mass causing a significant suppression of hole ionization coefficient, α h . Both Al x Ga 1– x As y Sb 1– y and Al x In 1– x As y Sb 1– y quaternary compounds are considered to have a potential for ≥2 μm wavelength optical communication band. Figure 5(b) shows F(M) versus M for InAs APDs compared with data for selected materials: HgCdTe and InAlAs. The F(M) values estimated for InAs p-i-n avalanche photodiodes do not follow McIntyre theory falling below the local field model assessed for k  = 0 being similar to the reported for SWIR HgCdTe and slightly higher than published for MWIR HgCdTe electron-initiated, e-APDs. This F(M) dependence on gain falling under the lower limit of the local field theory is related to “ dead space ” effect. As marked in the section “Background”, if the avalanche layer is thick, “ dead space ” may be ignored, and McIntyre local field theory correctly justifies the APD’s performance. The InAlAs APD F(M) dependence on M is comparable to the standard APDs where both electrons and holes undergo multiplication.

The progress in InAs electron-initiated, e-APDs’ fabrication allowed the ideal properties of avalanche multiplication and excess noise to transfer to the readily available A III B V materials system, enabling broader applications that were previously only possible with the less accessible HgCdTe system. The InAs APDs properties make them an attractive approach for a wide range of NIR and MWIR purposes, including active/passive imaging, LIDAR, and remote gas sensing.

A II B VI avalanche photodiodes

As reported by Leveque et al. it is possible to distinguish two regions of the Hg 1– x Cd x Te, x Cd chemical compositions where k  =  α h / α e is either much higher k » 1 or much lower than k «1 what was presented in Fig. 6(a) showing avalanche Hg 1– x Cd x Te capability dependence on the bandgap energy 45 , 46 . For a cut-off wavelength shorter than about λ c  < 1.9 μm ( x  = 0.65 for 300 K), authors estimated α e « α h due to the resonant enhancement of the hole multiplication coefficient when bandgap energy corresponds to the E g ≅ E SO  = 0.938 eV [see Fig. 6(c) ] what corresponds to the 1.32 μm. The case for k » 1 is favorable for low F(M) APDs with a hole-initiated multiplication effect. The electron-initiated multiplication effect is dominant for x  < 0.65. Both HgCdTe k regimes could be used for efficient APDs utilizing comparable SAM device structures.

figure 6

a the crossover between e-APD and h-APD. The crossover at E g  ≈ 0.65 eV corresponds to the λ c  = 1.9 μm for 300 K 46 . Hole-initiated avalanche HgCdTe photodiode: b detector profile, c energy band structure, d hole-initiated multiplication process energy band structure. The multiplication layer bandgap energy is adjusted to the resonance condition where the bandgap and the split-off valence band energy and the top of the heavy-hole valence band energy difference are equal. Electron-initiated avalanche HgCdTe photodiode: e diagram of electron-initiated avalanche process for HgCdTe-based high-density vertically integrated photodiode (HDVIP) structure (n-type central region and p-type material around), f electron avalanche mechanism, and g relative spectral response for 5.1 μm cut-off wavelength HgCdTe HDVIP at T  = 80 K

Figure 6(b–d) illustrates the APD device profile, energy band structure, and multiplication mode for hole-initiated avalanche (h-APD) HgCdTe photodiodes. In this case, the bandgap energy [ E g , see Fig. 6(c) ] corresponds to the energy difference between the top valence and the split-off light-hole band ( E SO ). Assuming the advantage of that regime, de Lyon et al. published on the back-illuminated multilayer SAM-APD deposited in situ by MBE on CdZnTe exhibiting λ c  = 1.6 μm and avalanche region, λ c  = 1.3 μm 47 . Multiplication gain within the ranges, M  = 30–40 at V  = 80–90 V reverse voltages for 25-element mini-arrays was demonstrated.

Originally, quite a few experimental papers were published to verify the predicted hole-to-electron impact ionization low ratios, k  < 0.1 values for Hg 1– x Cd x Te exhibiting cut-off wavelengths, λ c  > 1.9 μm 48 . In 1990, Elliott et al. predicted reasonable gain values, M  ~ 5.9 at low reverse voltages, V  = −1.4 V for electron-initiated LWIR HgCdTe APDs ( λ c  = 11 μm) 49 . The very first strong and persuasive benefits of the electron-initiated multiplication mechanism in the MWIR lateral-collection n + -n − -p APDs (p-type active layer) were published by Beck et al. in ref. 50 .

A concept presented by Kinch in his monograph (Chapter 7) explains in detail the high-value difference between electron and hole ionization coefficients ( α e  ≠  α h ) resulting from HgCdTe energy band diagram characteristics, including:

hole effective mass higher than electron one (holes exhibit lower mobility);

low optical phonons scattering rates;

two times lower electron multiplication threshold energy 51 .

The electron-initiated HgCdTe APDs have been designed and fabricated by DRS, BAE Systems Infrared in England, and Sofradir/Leti in France 52 , 53 , 54 . The most popular APD structures are presented in Table 4 . The DRS detector was referred to as an HDVIP, while BAE Systems Infrared reported on the loophole diode 55 , 56 . The avalanche process in HgCdTe HDVIP structure is illustrated in Fig. 6(e, f) . The carriers are photogenerated in the p-type active region (surrounding the center n-type avalanche region) and then diffuse into the multiplication region. If the reverse voltage increases within the range from 50 mV to several volts, the central n-type multiplication layer comes to be completely depleted where a high-electric field builds up accelerating low effective mass electrons to avalanche in HgCdTe low bandgap multiplication material. As is presented in Fig. 6(g) , the front side of the illuminated APD responds with high QE from the VIS to the IR cut-off wavelengths, however, due to the narrow bandgap energy of the compound building the avalanche layer, the APD requires severe cryogenic cooling.

Empirically determined electron multiplication gain ( M e ) for HgCdTe photodiodes at 77 K is equal:

with V th  ≈ 6.8 ×  E g for all Cd compositions from 0.2 <  x  < 0.5 50 . Figure 7(a) shows the measured gain dependence on the bias, V , together with DRS experimental data. The DRS HDVIPs experimental data shows nearly “perfect” APD characteristics/performance. The detector exhibits the homogenous exponential gain versus bias characteristic being consistent with k  =  α h / α e  ≈ 0. The F(M) data for photodiodes with a 4.3 μm cut-off wavelength shows no dependence of F(M) on M where F(M)  = 1.3 for M  > 1000 [see Fig. 7(b) ], proving that the electrons undergo the ballistic ionization process 57 , 58 . The high bandwidth large area pixels can be reached by joining the APDs with small capacitance in parallel (N × N configuration) due to the cylindrical junction geometry.

figure 7

a the experimental gain versus bias for selected cut-off wavelengths for DRS electron-initiated APDs at 77 K together with extra measured data points taken at ∼ 77 K 51 and LETI e-APDs at 80 K 59 , b constant F(M)  ~ 1 versus M at 80 K for 4.3 μm cut-off wavelength APD 135

More recently, there have been reports on other device structures confirming the important features of the electron-initiated multiplication mechanism—see Table 4 where schematic illustrations of the mesa heterojunction and planar homojunction are presented. Selex in Southampton (at present Leonardo) designed and fabricated the mesa heterojunctions (grown by MOCVD on GaAs substrates) with the energy bandgap and doping levels to be varied easily within the detector’s architecture. Both the absorber and avalanche regions are individually adjusted. Every pixel is electrically screened by a mesa slot extending through the active layer to suppress lateral-collection and blooming.

The HgCdTe Leti/Sofradir planar p–i–n homojunctions with sizable n-regions are processed by the n-type conversion. The vacancy-doped p-type ( N a  = 3 × 10 16  cm –3 ) thin layer next to the surface is converted into a n + type to the doping level, N d  = 1 × 10 18  cm –3 54 . During processing of the n + type doping, n − layer is formed by the Hg vacancies reduction to the typical epitaxy residual doping level N d  = 3 × 10 14  cm –3 . The broadening of the lightly doped n − layer is associated with the thickness of the highly doped n + region.

The highest gain-bandwidth product, GBW  > 16 THz was reported by Leti/Sofradir APDs 59 . Figure 7(a) shows typical gain curves reached and presented by LETI for selected electron-initiated APDs versus cut-off wavelengths at 80 K.

Perrais et al. reported on the utmost gain, M  = 5300 at V  = −12.5 V for MBE-grown 30 μm pitch p-i-n HgCdTe planar APD deposited on a CdZnTe with 5 μm cut-off wavelength 60 . As shown in Fig. 7(a) , the utmost M normally follows an exponential trend with reverse bias and cut-off wavelength.

The standard performance of the HgCdTe avalanche photodiode at temperature 80 K is presented in Table 5 61 . The highest gains stay within the range from 2000 for SWIR photodiodes up to 13,000 in MWIR devices and agree with the maximum stable gain values. Those such high gain values depend on the APD’s observation time, dark current noise, and the noise of the detection electronics. The SWIR APDs are characterized by a stable gain related to the low noise, up to 300 K.

Electron-initiated HgCdTe APDs allow additional advantages for the focal plane arrays (FPAs) fabrication for SWIR and MWIR ranges. These detectors are being used for gated-active/passive imaging—see section “Avalanche photodiodes in active imaging systems”. Table 4 collects the performance of the most advanced HgCdTe APD FPAs. The first demonstration of 24 μm pitch APD 320 × 256 laser-gated imaging FPA was reported by Baker et al. in Selex 53 . Selex reported on the 4.2 μm cut-off wavelength APDs exhibiting multiplication gains up to 100, low excess and input noises being equal to the photon noise at the level of 15 photons rms for 1 μs integration times. Lately, Selex and Leti have designed and fabricated those devices for space purposes 61 , 62 . Selex has also reported on the full-custom silicon read-out integrated circuit (ROIC) for SAPHIRA (Selex Advanced Photodiode Array for High Speed Infrared Array). That 24 μm pixel pitch 320 × 256, FPA is developed for wavefront sensors and interferometry applications in the space telescopes, and its specification and performance are included in Table 6 . The present version of SAPHIRA FPAs has exhibited sensitivity within the range 0.8–2.5 µm, QE  > 80%, short-time response, M  > 500, and sub-electron effective read noise (~0.1e − rms) at 1 kHz frame rate and operating temperatures, T  = 90–100 K 63 .

The University of Hawaii together with partners (Leonardo corporation, Markury Scientific, and Hawaii Aerospace) driven by the SAPHIRA performance has started to develop a 15 μm pixel 1k × 1k FPA appropriate for ultra-low background IR space applications, reaching dark current, J Dark  < 0.001 e − /pix/s and a read noise <0.3 rms e − /pix/frame 64 .

The French company, First Light Imaging developed the C-RED One camera with SAPHIRA detector developed by Selex. The camera is cryogenically cooled by an integrated pulse tube. The latest version of the camera with an f /4 beam aperture is characterized by a dark current induced by a blackbody at 80 K of 30–40 e − /s at a gain, M  = 10 65 .

Superlattice avalanche photodiodes

The APDs’ noise may be suppressed not only by the selection of the materials exhibiting high ionization coefficients but also with thin/scaled multiplication regions. Further suppression is expected and confirmed by the implementation of the new materials (“ third wave ”) and impact ionization engineering ( I 2 E ) with correctly constructed and fabricated structures. The I 2 E architectures that have reached the lowest F(M) use avalanche layers where carriers are transported from a wide energy gap material to adjacent low bandgap semiconductors.

Prior to the development of bulk-based APDs, photomultiplier tubes (PMTs) were considered to be the preferred detector family for ultraviolet (UV) and NIR applications. Those detectors convert impinging photons to electrons on a photocathode and electrons are multiplied via a series of dynodes to a final anode [see Fig. 8(a) ]. The arrival of an electron causes additional electrons to be released by every dynode producing high gain being scaled by a number of dynodes and the bias deposited on dynodes. PMTs are reported still to be used for some purposes, mainly due to their high sensitivity. On the other hand, PMTs are colossal, unstable, and require extremally high voltage which limits their potential applications.

figure 8

a schematic presentation of a photomultiplier tube, b multi-quantum well p-i-n APD energy band sketch with marked intrinsic region (i), c energy band profiles of staircase APD under zero (top) and reverse (bottom) voltage. Multistep AlInAsSb staircase avalanche photodiode: d 3-step staircase APD device profile, e theoretically calculated by Monte Carlo method and measured gain of 1-, 2-, and 3-stairs APDs for 300 K 70 . MWIR SAM-APD structure with AlAsSb/GaSb superlattice: f device design profile, g energy band structure under reverse voltage, and h carriers impact multiplication coefficients versus reciprocal electric field at 200 K 73

The considerations in the section “Background” suggest that discrete localization of impact ionization effects and single-carrier multiplication are needed for the APD to reduce noise. The APD’s frequency response is conditioned by the carrier avalanche mechanism and the transit time, with the frequency response mostly being higher than the transit time due to the multiplication build-up time. In turn, the multiplication build-up time is conditioned by the electrons and holes ionization rates. Considering a heterojunction system with different conductivity and valence band edge discontinuities, the electron multiplication rates may be increased.

In 1982, for the first time, Capasso et al. presented the APD model simulating the functionality of a PMT 66 , 67 . This idea was examined in the multi-quantum well AlGaAs/GaAs APD shown in Fig. 8(b) . Due to the fact that the conduction band offset (CBO) is higher than that at the valance band offset (VBO), the electron multiplication coefficient is higher than holes at the heterojunction interface. Further investigations showed that there is a lack of enough CBO and energy difference between the direct and indirect valleys of GaAs/AlGaAs for the staircase gain mechanism. In general, however, the above proposal has not been limited to GaAs/AlGaAs and other semiconductor systems have been widely used so far 68 . The biased staircase design shown in Fig. 8(c) prompts the single-carrier, electron-initiated avalanche process, while the hole-initiated multiplication is restricted by the lack/(small) of valence band discontinuity.

More recently published papers have shown that AlInAsSb/GaSb staircase APD with a near-ideal gain of 2 per stair allows to reach highly deterministic and low-noise operation 69 , 70 . Fig. 8(d) presents the schematic profile of a three-step AlInAsSb staircase APD and a demonstration of deterministic ~2 n gain dependence ( n —number of stairs). As is shown, the stepped regions are composed of digital alloy grading between Al 0.7 In 0.3 As 0.31 Sb 0.69 and InAs 0.91 Sb 0.09 . The both bottom and top of the mesa structure are doped at moderate levels of acceptor and donor concentrations to form contact regions. Within the upper 600 nm of the mesa, generated electrons reach the energy by diffusion in the p-contact layer and E drift in the uniform Al 0.7 In 0.3 As 0.31 Sb 0.69 unintentionally doped region. The electric field dropped on the stepped region allows electrons (discrete multiplication process) to gain enough energy for low-noise collision ionization 69 . As can be seen, the gain is multiplied from zero to ~2 n with reverse bias increasing to the level that all device stages reach a stepped state. At higher reverse voltage the gain increases above 2 n which is caused by band-to-band tunneling through InAs 0.91 Sb 0.09 energy gap in the stages. Monte Carlo simulation results coincide well with the experimental data presented in Fig. 8(e) where to gain for 1-, 2-, and 3-stairs devices reach 1.77, 3.97, and 7.14 being comparable with numerically estimated values 2.01, 3.81, and 6.71.

Type-II superlattices (T2SLs) meet the bandgap requirements for APDs’ fabrication exhibiting high performance to include gain and low noise, and a single or dominant electron- or hole-initiated avalanche process in SWIR and MWIR ranges 71 , 72 , 73 , 74 . The “Ga-based” SLs have much larger VBO and CBO than the InAsSb layers in the “Ga-free” T2SLs. The T2SLs energy bandgap is conditioned by the SLs period and the Sb chemical fraction. Varying the width of the layer, C 1 may be positioned between the InAs and GaSb conduction bands (CBs), while HH 1 may be placed between their valence bands (VBs). The C 1 band is more sensible to layer width than HH 1 caused by the high GaSb heavy-hole mass (~0.41 m o ). It was proved that the GaSb layer width has negligible influence on the T2SL energy bandgap, but due to the tunneling of InAs electron wave functions via GaSb barriers, the GaSb width significantly contributes to the conduction band dispersion. It must be stressed that the selection of the layer widths demands more information of the strain impact on the material quality because the SL constituent layers are not lattice matched. In terms of the “Ga-free” InAs/InAsSb T2SLs, a fairly thick InAs layer is needed to balance the strain on the thinner InAsSb (the InAs is under a small tensile strain and InAsSb is under large compressive strain).

In recent years, a new material system based on antimony-strained layer superlattices has emerged, attracting much interest with prons such as high material homogeneity, high bandwidth tunability, and Auger recombination suppression. However, in the case of MWIR APDs based on InAs/InSb T2SLs, their performance is limited by the equality of α h  =  α e 71 .

Razeghi et al. have demonstrated the MBE-grown MWIR SAM-APD device [see Fig. 8(f, g) ] which consists of AlGaAsSb/InAs 0.9 Sb 0.1 multi-quantum well as a multiplication layer 73 . The AlAs 0.1 Sb 0.9 /GaSb T2SLs were assumed to be the barrier of the multi-quantum well structure. This design of the multiplication layer provides high flexibility in the energy band engineering, allowing for large differences in electrons and holes ionization rates, which can be seen in Fig. 8(h) . The maximum multiplication gain increases from 29 (under −14.7 V) at 200 K to 121 at 150 K.

Low-dimensional solid avalanche photodetectors

The extraordinary and unusual electronic and optical capabilities of low-dimensional solid materials make them be capable of avalanche photodetector applications. In the last decade, many avalanche photodetectors have been demonstrated using nanowires (coupled with plasmonic and photonic crystals) and two-dimensional (2D) layered materials 8 . So far, however, the main research activity is focused on devices operating in VIS and SWIR regions. For this reason, this section will only briefly describe the most interesting and published results.

The nanoscale photodetectors exhibit relatively low sensitivity. A way to enhance their responsivity is the avalanche multiplication mechanism observed, for example, in Si-CdS p – n heterojunction photodetector based on nanowire structure, or in an InAsP quantum dot after tunneling into InP avalanche nanowire photodiode 75 , 76 . In 2019, Farrell et al. published on the isolated absorption and impact ionization regions avalanche photodiode array of 4400 InGaAs/GaAs nanowires 77 . This array design greatly improves the volume of the multiplication area and the number of filled traps. However, this innovative APD design requires a cryogenic operation which limits its widespread applicability.

2D materials originate directly from layered van der Waals (vdW) solids. The plane atoms are coupled by ionic or covalent bonds, while layers are linked by weak vdW interactions allowing that 2D material could be fabricated by mechanical exfoliation from bulk source materials. In addition, weak vdW bonds allow possible combinations of the 2D materials providing flexibility in heterostructure design.

Different types of 2D photodetectors with the flexibility in forming heterostructures have already been widely studied with the advantages of weak vdW interactions. The most popular are photoconductive, photovoltaic, phototransistor (hybrid detectors), and photothermoelectric 78 . However, the avalanche mechanism through impact multiplication has not yet been researched thoroughly in 2D photodetectors. In this review, our discussion is focused on the avalanche effect in 2D layered materials and their vdW heterostructures. 2D layered graphene, being gapless, makes it difficult to construct high detectivity photodetector. On the other hand, an alternative to graphene—2D materials [like black phosphorus (BP), InSe] and their heterojunctions (like BP/InSe, BP/MoS 2 , MoS 2 ( E g  = 1.8 eV)/p-type Si ( E g  = 1.1 eV)) exhibit promising avalanche performance in VIS to NIR ranges 8 .

In order to observe the avalanche mechanism, Lei et al. applied more than 50 V reverse bias voltage into a 2D InSe field effect transistor, resulting in a large Schottky barrier between Al/InSe junction on Si substrate and 285 nm-thick SiO 2 layer 79 . At a bias voltage above 12 V, the E in InSe is large enough to speed up photogenerated electrons and generate electron-hole pairs by carrier multiplication. Further increase of the voltage (>50 V) causes the metal/semiconductor junction breakdowns leading to the dramatic rise of both photocurrent and dark current and lowering signal-to-noise ratio. Also, Atalla et al. have observed increasing in photocurrent versus bias voltage in the Ti/BP Schottky barrier due to the avalanche effect 80 . Comparable results were reported by Gao et al. on the avalanche effect in the graphite/InSe Schottky detector [see Fig. 9(a) ] 81 . Due to the quantum confinement effect caused by the vdW gap in the layered InSe, two different carrier processes can be distinguished in that device. As presented in Fig. 9(b) , the vdW ~1.85 eV gap acts as a tunneling barrier that limits the out-of-plane charge transport, causing the dimensionality of the electron-phonon (e-ph) scattering to decrease and the increase of the Coulomb interaction. As the e-ph scattering is limited the multiplication rate will be boosted resulting in higher M at lower breakdown biases. The high gain is reached by the dimensionality reduction of the e-ph scattering in the 2D material which was presented in Fig. 9(b) . Unlike conventional avalanche devices holding the positive temperature coefficient of the threshold voltage, the demonstrated device exhibits the negative temperature coefficient presented in Fig. 9(c) .

figure 9

a graphite/InSe Schottky avalanche detector - injection, ionization, collection electron transport mechanisms, b e-ph scattering dimensionality reduction affects electron acceleration process and gain versus electric field in 2D (red line) and 3D (blue line), c breakdown voltage ( V bd ) and gain as a function of temperature—exhibits a negative temperature coefficient 81 . Nanoscale vertical InSe/BP heterostructures ballistic avalanche photodetector: d schematic of the graphene/BP/metal avalanche device 83 , e ballistic avalanche photodetector operating principle, f quasi-periodic current oscillations, g schematic of the graphene InSe/BP 83 , h I ds –V ds characteristics for selected temperatures (40 − 180 K), i avalanche breakdown threshold voltage ( V th ) and gain versus temperature—showing a negative temperature coefficient. Pristine PN junction avalanche photodetector: j device structure, k as the number of layers increases, a positive/negative signal of SCM denotes hole/electron carries, l APD’s low temperature (~100 K) dark and photocurrent I–V curves 87

In the case of vertically stacked BP/InSe heterostructure, the ballistic avalanche effect was observed where the carriers ionization probabilities are comparably caused by their symmetric band structure 82 . Zhang et al. also fabricated an InSe/BP heterojunction where the ballistic avalanche effect can be observed 83 . The schematic diagram of the mechanism corresponding to the ballistic avalanche process is presented in Fig. 9(e) . The electric field can make the hole accelerate to get enough energy to produce the carriers pair in one pass to plane “A”, and in this way, two holes can be collected, while the electron is transported into the channel. A step further, the electron can generate another electron-hole pair by impact multiplication, and this is collected by plane “B” and the hole drift back to the channel in the repeating cycle.

When the channel length is shorter in comparison to the carrier mean free path, the character of the carrier transfer will change dramatically. Specifically, the transport of electrons within the average free range will no longer be affected by any scattering. That allows to limit noise and power consumption of the photodetector. In Fig. 9(f) , the current curves exhibit a quasi-period oscillation denoting the ballistic transport of the BP channel. The InSe/BP device exhibits a negative temperature coefficient, as presented in Fig. 9(i) . That comes from the broadening of the Fermi-level and band-bending shift caused by thermal-expansion 83 .

The 2D/3D systems are especially promising for avalanche photodiode technology, where 2D materials can be used for active layers while 3D Si as a multiplication region [see Fig. 9(j) ] 84 . Once illuminated, the incident photons generate the carrier pairs being accelerated by bias at the heterointerface. The 2D/3D vdW interface prevents lattice mismatch problems allowing to reach high-quality heterojunctions. As mentioned 2D MoS 2 proved to be a proper material for APDs fabrication 84 , 85 , 86 . In addition, the APDs can be fabricated by the different number of MoS 2 layers. Xia et al. reported on the homojunction transistor based on MoS 2 . As the number of layers changes, 2D MoS 2 exhibits different doping characteristics, as shown in Fig. 9(k) 87 . This natural p – n homojunction exhibit a well-defined interface. The device under the illumination of 0.42 mW/mm 2 and wavelength 520 nm with the bias voltage −4.5 V can photogenerate large amounts of electron-hole pairs, as illustrated in Fig. 9(l) . For a conventional avalanche conditions, the external electric field is large enough, and electrons or holes can get sufficient energy to achieve avalanche breakdown. It is suggested that the effect is conditioned by the ionization of electrons in the outer layer producing secondary carriers 87 .

The detailed comparison of the APDs performance among 2D material family detectors was presented in Table 7 . The responsivity ( R ), response time ( RT ), operating wavelength ( λ ), dark current ( I Dark ), external quantum efficiency ( EQE ), normalized photocurrent-to-dark current ratio ( NPDR ), avalanche gain ( M ), and operating temperature ( T ) with proper reference were presented. The highest gain 10000 was reported for BP/InSe (operating wavelength 4 μm, at 10–180 K) and 903 for MoS 2 (operating wavelength 633 nm, at 300 K) 81 , 84 .

Large dark current in, e.g., multilayer 2D-based detectors has been found to be a main problem hampering further progress. In order to limit the dark current, the typical approach is the source-drain-gate detector with the ability to carrier concentration monitoring in the channel. In comparison to the two-, the three-terminal detector makes the structure more complicated and the continuous gate voltage is energy-consuming. An additional common approach is to implement heterojunctions formed by the connected TMDs. That may successfully suppress dark current and improve performance, however, the depositing process of TMDs on the different materials is difficult and inefficient, making that technique hard for large-scale applications. Lately, organic-inorganic hybrid perovskites (OIHP) were reported to exhibit the potential to increase detector performance due to remarkable capabilities (broadband absorption coefficient, direct bandgap). In addition, OHIP could be deposited by the not complicated, low temperature, and low-cost spin-coating techniques. By depositing 2D OIHP on a multilayer MoS 2 device, the nominal dark current was remarkably reduced by six orders of magnitude 88 .

Lately, 2D materials have been implemented to fabricate THz detectors 89 . The bP exhibiting direct bandgap for bulk ( E g  ≈ 0.35 eV) and monolayer ( E g ≈ 2 eV) phases, significantly large mobility (>1000 cm 2 /Vs) make that material an appropriate candidate for the THz detection. Viti et al. presented the bP THz detector operating at 300 K in 2015 90 . Authors used the mechanically SiO 2 -encapsulated bP flake in an antenna-coupled top-gate FET where a typical bonding tape method was implemented to move the flake on a 300-nm SiO 2 layer on the top of a 300-µm thick Si. The photodetection mechanism in bP-based THz FETs was found to be based on the result of three effects including photothermoelectric, bolometric, and plasma-wave rectification effects 90 . Noise equivalent power ( NEP ) for listed mechanisms reaches ~7 nW/Hz 1/2 , ~10 nW/Hz 1/2 , and ~45 nW/Hz 1/2 for the bolometer, plasma-wave, and thermoelectric detector, respectively. The responsivity of ~5–8 A/W at 0.3 THz allows to apply a bP FET detector for real-time quality control and pharmaceutical purposes 91 . To avoid influence of the ambient temperature on the exfoliated bP flake, Viti et al. incorporated a bP flake within a multilayered structure to form hBN/bP/hBN THz FET devices allowing to reach NEP  ~ 100 pW/Hz 1/2 and voltage responsivity, R v  ~ 38 V/W at 4 K (at 295 GHz) and ~10 nW/Hz 1/2 and ~2 V/W at 300 K, respectively. Viti et al. presented the latest progress on the bP photodetectors operating in the spectral range 0.26–3.4 THz focusing on the possible issues and challenges in the device’s processing and fabrication 91 , 92 .

Lately, it has been presented that topological insulators (TI) exhibit potential for a wide spectral range including THz detection. TIs are being considered as an advanced quantum phase of matter, characterized by a semiconducting bulk and topologically protected surface states with a spin and momentum helical locking and the Dirac-like band structure 93 , 94 . 2D TIs could be connected with gapless edge states and 3D insulators with gapless topological surface states (TSS) 95 .

An advantage of THz plasmonic with TIs is connected with the THz radiation rectification via excitation of plasma waves in the antenna-coupled FETs active channel. The very first presentation of THz detection facilitated by TSS in top-gated nanometer FETs using thin Bi 2 Te 3− x Se x flakes was shown by Viti et al. in ref. 96 . The maximum R v  ~ 3.0 V/W and the minimum NEP  ~ 10 nW/Hz 1/2 was reached for 292.7 GHz. Yao et al. presented TI THz heterojunction Bi 2 Te 3 -Si device 97 . The pioneering approach for THz detection at 300 K using a subwavelength metal-Bi 2 Se 3 -metal structure exhibiting 300 K R i  ~ 75 and 475 A/W for 0.3 THz operating in the self-powered and voltage modes was shown by Tang et al. 98 . The measured NEP  ~ 3.6 × 10 −13  W/Hz 1/2 and D *  ~ 2.17 × 10 11  cmHz 1/2 /W were reached for V  = 50 mV.

Avalanche photodiodes in active imaging systems

Thermal imaging systems are divided into passive and active devices. The typical night vision system is based on thermal imaging cameras. In this case, the imaging device does not emit any energy but only acts as a receiver. Conversely, when a source is used to light and gather the reflection from the target, the camera can be considered an active system allowing to obtain images during the day and night, under different illumination conditions.

Figure 10(a) illustrates the range-gating technology system in conjunction with other sensors. The range-gating technology consists of a pulse laser (typical wavelength, λ  = 1.55 μm), laser receiver (for ranging), gated detector, wide field of view ( FOV ) thermal imager and monitor electronics. A light pulse is emitted toward an object. Once the reflected light returns from the target, the accompanied high-speed electronic shutter activates at the appropriate moment. The detector must meet stringent requirements for high sensitivity and extremely high-frequency response and is a main, performance-driven part of the system.

figure 10

a operation principle [at t 0 —camera is closed—light pulse is emitted, at t 1 —target reflects light pulse, at t 2 —the camera is opened for a short period ( ∆t ) matching the needed depth of view]; b typical images of wide FOV thermal and laser-gating systems 53

The gating technology allows to select an exact piece of space so that operator can see the target location, without parasitic lights or light scattering by aerosol particles. Selecting gating width (a narrow enough slice of space), the system significantly increases the detectivity. The typical images generated by the wide FOV thermal camera and the laser-gated imaging are shown in Fig. 10(b) .

Between different active imaging systems, 3D pulsed-laser LIDAR using APD arrays has drawn attention due to its simple operation principle, high interference immunity, and long imaging distance range 99 , 100 . There are two types of flash LIDARs available: the linear and the Geiger modes. When linear mode is activated, the reverse voltage on the APD is lower than the breakdown bias and carriers are taken up faster than being generated, causing the avalanche process to terminate itself. In this case, the output photocurrent generated by the finite gain is a linear function of the echo pulse intensity. The APD operates at Geiger mode when the reverse voltage exceeds the APD’s breakdown bias. Photoexcitation of the single carrier can cause the multiplication current peak to be high enough to be detected by the threshold detection circuit, making the detection process noiseless because it is inherently digital.

The APD’s spectral response depends on the material used in the absorption region. Silicon APDs have a sharp cut-off wavelength close to 1 μm. In this case, a 905 nm light pulse can be absorbed in eye vitreous humor and lead to possible retina destruction at fairly moderate laser powers (the laser is focused by the lens on the small retina spot). The systems equipped with InGaAs APDs can use lasers being safe for the eye (traditionally 1.55 μm) to minimize damage to the users’ eye (the SWIR beam with a wavelength exceeding ~1400 nm is powerfully absorbed by eye parts before reaching the retina). HgCdTe APDs operate in linear mode and exhibit QE close to 90% in a wavelength range of 5 μm. Table 8 collects the pulsed-laser 3D imaging flash LIDAR performance incorporating the linear-mode APD arrays.

The putting the new APDs technology into the market, except for performance and potential applications, two key factors should be taken into consideration: fabrication readiness and budget efficiency. Currently, a uniform integration process must be developed to allow the 2D material-based APDs to be matching with the current CMOS technology to reach improved parameters at a reasonable cost. Table 9 compares the existing and well-developed A III B V , A II B VI material technologies with emerging 2D materials for APDs fabrication 101 . It must be underlined that even though both A III B V and A II B VI materials have established themselves as standard for APDs and hold the leading position in the existing IR market, certain elementary restrictions which have not been circumvented yet. It must be underlined that after 60 years of technological development, the ultimate A III B V and A II B VI APDs HOT detection parameters have not been reached. The A II B VI (HgCdTe) semiconductor instability and high lattice mismatch (A III B V materials) generated strain create defects limiting the devices’ performance. Another key issue is the high fabrication/processing cost, extremely complicated growth techniques, and sophisticated device architectures. 2D APDs on the other hand, could be easily processed to include device design, substrates selection, and fabrication methods. The 300 K operation of 2D material-based APDs is the most crucial feature conditioning their cost-effectiveness. The 2D material-based APDs have been reported to exhibit the remarkable capability to substitute the typical APDs in relation to the gain, dark current suppression, excess noise, I 2 E engineering, and operating temperature. It must be stressed that the thin layers building 2D APDs enable flexibility in impact ionization coefficients tuning leading to dark current suppression and low power usage in comparison to commercial devices based on well-developed bulk materials.

The detectors for optical telecommunication applications and quantum information technologies have mainly pushed the APDs to progress with high BW , low F(M), and high GBW from 1975. It was shown that the APD provides better parameters in comparison to typical p–n or p-i-n-based devices including detectivity, gain, and time response. It is visible that APDs have been successfully applied into the variability of applications, however, the chase to suppress the random noise [to achieve F(M)  < 2] related to the multiplication nature has been constant because the excess noise restricts the detector’s sensitivity, detectivity and reduces the operating BW . The solution is a higher and fully controlled—deterministic impact ionization mechanism which can be achieved either by the proper multiplication material selection, by device design (scaling/thin multiplication regions), or by material engineering. It was demonstrated that the non-local effect of impact multiplication allows to limit of the noise in many materials covering the wide radiation range. In addition, the “ third wave ” materials and related technologies have opened the prospect of I 2 E to design and fabricate heterojunctions to further suppress noise and reach higher GBW .

It must be stressed that the APD’s yield is highly conditioned by sufficient GBW being strictly related to the F(M) . The conditions and variables allowing to reduce noise contribute also to high GBW . Therefore, the GBW increase and F(M) suppression have been an effort for the progress and investigation. The following methods to improve APDs performance must be implemented:

1) choosing a material with advantageous carrier multiplication coefficients. The APD’s avalanche layer contributes to the M , F(M) , and GBW products. The local-field multiplication model explains that the APDs F(M) and GBW are conditioned by the material’s carriers multiplication coefficients in the avalanche layer. Higher detection parameters are reached if one of the multiplication coefficients is substantially higher than the other, i.e., the k  =  α h /α e differs significantly from unity. Attempts to increase APD’s parameters have moved to electric field profile optimization and research on the new compounds to include bulk A III B V , A II B VI , “ third wave ” materials and technologies—T2SLs InAs/GaSb, “Ga free”—InAs/InAsSb and 2D materials. Flexibility in bandgap energy tuning and the energy band profile optimization in 2D materials makes the impact ionization be monitored by the number of layers modification. It is feasible to adjust the k  =  α h /α e level by varying the number of 2D materials constituting layers. For bulk and “ third wave ” avalanche layers, the minimal F(M) has been reached with materials such as Si, HgCdTe, InAs, Al x Ga 1– x As y Sb 1– y , Al x In 1– x As y Sb 1– y , T2SLs InAs/GaSb, and MoS 2 exhibiting k « 1);

2) thickness reduction (scaling) of the avalanche layer to utilize the non-local nature of the multiplication process [reducing the thickness of the multiplication layer leads to lower F(M) ]—proved for many bulk materials used for avalanche regions: InP, GaAs, In 1– x Al x As, Si, Al x Ga 1– x As, SiC, GaP, GaInP). As 2D materials-based APDs are inherently reduced to the submicrometer level, the absorbers based on those materials are under large lateral electric fields leading to the breakdown;

3) I 2 E using appropriately designed heterojunctions. The lowest F(M) could be reached by using impact ionization layers where electrons are transported from a wide energy bandgap material to the bordering low bandgap semiconductor. The electrons’ energy increases in the wide bandgap layer but high threshold energy prevents them from multiplication. Next, the high energy electrons are transported to the low threshold energy, narrow bandgap layer where they are being immediately multiplicated. The conduction band discontinuity ensures extra energy to enhance that process. The generated holes are promptly transported to the wide bandgap layer where multiplication is much more limited. It must be stressed that both effects reduce F(M) due to the fact that gain is much more one-carrier prompted and occurs with a higher probability. Among the most commonly used heterojunctions could be listed: (GaAs/Al x Ga 1– x As, In 0.52 Al 0.48 As/In 0.53 Ga 0.17 Al 0.3 As, InAlAs/InAlGaAs—cascade/tandem/multistage structures, Al x Ga 1– x As/GaAs and Al 0.7 In 0.3 As 0.31 Sb 0.69 /InAs 0.91 Sb 0.09 —staircase, InSe, BP/InSe, MoS 2 , BP, MoTe 2 –WS 2 –MoTe 2 , 2D vdW). Here, 2D material-based APDs exhibit potential in developing ultrathin and favorable miniature devices. Typical bulk materials APDs are restricted by reasonably high dark currents. That problem could be resolved by nanomaterials and nanostructures incorporation (due to the Schottky barriers) as APDs absorbers.

The APDs can operate below or above breakdown bias for many applications. When the APD operates below breakdown voltage, the avalanche gain is fixed, meaning that the device may be used for photon energy selection, while when the detector operates above the breakdown bias (Geiger mode: single-photon detection regime), the photon may activate multiplication breakdown, causing substantial carrier avalanche allowing single-photon detection. Recently an impressive increase in interest in new SPD technologies has been observed due to massive internal gain, short-time response, high sensitivity, small volume, and flexibility in integration. Its device performance including SPADs has been increased via external quenching circuits and device structure optimization. The main reason for that trend is unquestionably the move for QKD. Effective single-photon counting, with a single-photon detection efficiency >50% was reached only for wavelengths <2 μm. That spectral region is mainly covered by SNSPDs providing remarkable performance but their applications are restricted by the cryogenic cooling requirements. Conversely, SPADs circumvent the inherent restrictions of SNSPDs by possible 300 K operation by A III B V material leader—InGaAs. Extension of the SPD performance to MWIR (>2 μm) exhibits prospective to be applied in astronomy, LIDAR, research on dark matter, and the elementary investigation of molecules.

Once APDs based on typical bulk materials have reached a high level of development and are broadly used for quantum information purposes for single-photon detection, to meet the demanding technologies in the long-range field such as FSO, LIDAR/LADAR, ToF, intelligent robotic and in battlefield conditions (military applications) the 2D material detectors are speedily designed, developed, assessed and implemented. 2D semiconductors allow implementing of new approaches for sophisticated APDs’ development by effective carrier ionization at the low-dimensional level enabling broad potential in the area of photon-counting purposes.

Further optimization of the APD performance is possible allowing to design and fabrication of devices with supreme parameters over conventional avalanche devices. For instance, by choosing 2D materials with promising band alignments and structures, it is feasible to implement appropriate Schottky junctions to suppress the dark currents and widen operating wavelengths. Moreover, improvement in processing allows us to reduce the response time and current noise. The 2D APD has been reported to be operating within VIS, NIR and MWIR ranges with a R i  ~ 80 A/W, EQE  ~ 24.8%, and M  ~ 10 5 for MWIR [ λ  = 4 μm, T  = 10–180 K, BP/InSe APD].

That paper has reviewed the multiplication effect generated by the avalanche process and sketchily reviewed the latest research on bulk and “ third wave ” APDs. The progress in the development of the APD operating in the IR range was presented covering materials based on HgCdTe as well as A III B V alloys including “Ga-based” and “Ga-free” T2SLs. The non-local characteristic approach and technological achievements have opened up the option of multiplication engineering incorporating different materials and heterojunctions to reach better performance: suppressed noise with higher GBW in broader spectral regions. It is believed that the 2D/vdW APD could prove itself to be an alternative to the bulk multiplication devices providing a possible method for developing devices exhibiting high sensitivity and low excess noise.

Data availability

All data generated or analyzed during this study are included in this published article.

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Acknowledgements

This research was funded by The National Science Centre, Poland—grant nos. UMO-2019/33/B/ST7/00614, UMO-2021/41/B/ST7/01532, and Science and Technology Commission of Shanghai Municipality—grant no. 23WZ2500400.

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Martyniuk, P., Wang, P., Rogalski, A. et al. Infrared avalanche photodiodes from bulk to 2D materials. Light Sci Appl 12 , 212 (2023). https://doi.org/10.1038/s41377-023-01259-3

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    Methods and methodology in the context of research refer to two related but different things: method is the technique used in gathering evidence; methodology, on the other hand, "is the underlying theory and analysis of how a research does or should proceed" (Kirsch & Sullivan, 1992, p. 2). Similarly, Birks and Mills (2011, p.

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    The objective of preparing a research proposal would be to obtain approvals from various committees including ethics committee [details under 'Research methodology II' section [ Table 1] in this issue of IJA) and to request for grants. However, there are very few universally accepted guidelines for preparation of a good quality research proposal.

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    Step 1: Title and Abstract. Select a concise, descriptive title and write an abstract summarizing your research question, objectives, methodology and expected outcomes . The abstract should include your research question, the objectives you aim to achieve, the methodology you plan to employ and the anticipated outcomes.

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    It puts the proposal in context. 3. The introduction typically begins with a statement of the research problem in precise and clear terms. 1. The importance of the statement of the research problem 5: The statement of the problem is the essential basis for the construction of a research proposal (research objectives, hypotheses, methodology ...

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  15. How To Write A Research Proposal

    1. Title and Abstract Choose a concise and descriptive title that reflects the essence of your research. Write an abstract summarizing your research question, objectives, methodology, and expected outcomes. It should provide a brief overview of your proposal. 2. Introduction:

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    1. Title Page: Include the title of your proposal, your name or organization's name, the date, and any other relevant information specified by the guidelines. 2. Executive Summary: Provide a concise overview of your proposal, highlighting the key points and objectives.

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  19. How to Write an APA Methods Section

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    Choosing an optimal research methodology is crucial for the success of any research project. The methodology you select will determine the type of data you collect, how you collect it, and how you analyse it. Understanding the different types of research methods available along with their strengths and weaknesses, is thus imperative to make an ...

  22. Research Methodology

    Definition: Research Methodology refers to the systematic and scientific approach used to conduct research, investigate problems, and gather data and information for a specific purpose. It involves the techniques and procedures used to identify, collect, analyze, and interpret data to answer research questions or solve research problems.

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