Charge Traps in Wide-Bandgap Semiconductors for Power Electronics Applications

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript provides a summary of recent advancements in understanding defects in wide bandgap (WBG) semiconductors and their applications for power electronics. At its current stage, however, the discussion is somewhat simple, and a major revision is needed to enhance its scientific rigor. My detailed suggestions for improvement are as follows:

 

1. While the introduction highlights the advantages of WBG semiconductors, it would benefit from a more in-depth discussion on why specific materials such as 4H-SiC, GaN, and β-Ga2O3 are critical for power electronics. Are there other significant WBG semiconductors that should be considered?

 

2. The review of characterization techniques (DLTS, TSC, PL) is useful. However, a brief overview of the strengths and limitations of each method, as well as their relevance to WBG semiconductors, would offer a clearer perspective on their application in defect analysis.

 

3. More detailed information is needed regarding the specific mechanisms behind defect formation. Additionally, the manuscript should address how these defects affect device performance under various operating conditions.

 

4. If there have been significant theoretical developments, these should be included. Adding a section on relevant theoretical investigations would provide a more comprehensive overview and deepen the reader's understanding of the subject.

 

5. The conclusions and perspectives section currently provides a simplistic summary of the results discussed earlier. It lacks important insights into future directions and emerging trends. This section should be expanded to highlight significant findings and suggest potential avenues for future research.

 

6. As a review paper, it is crucial to cite more recent references to accurately reflect the latest developments in the field.

Comments on the Quality of English Language

Moderate editing of English language required.

Author Response

Comment 1: While the introduction highlights the advantages of WBG semiconductors, it would benefit from a more in-depth discussion on why specific materials such as 4H-SiC, GaN, and β-Ga2O3 are critical for power electronics. Are there other significant WBG semiconductors that should be considered?

Response 1: While this review focused on 4H-SiC, GaN, and β-Ga₂O₃, attention should in the future also be directed towards emerging ultra-wide bandgap materials such as aluminium nitride (AlN),  diamond, and boron nitride (BN). However, due to immature fabrication technology, there is not enough data for now; thus, the review is comparing the most studied and envidioned materials. Appropriate comment was included in modified manuscript (Lines 477-482)

 

Comment 2: The review of characterization techniques (DLTS, TSC, PL) is useful. However, a brief overview of the strengths and limitations of each method, as well as their relevance to WBG semiconductors, would offer a clearer perspective on their application in defect analysis.

Response 2: Thank you for your kind suggestion. The characterisation techniques have been discussed in detail and the mutual comparison of methods was done in the revised manuscript (Lines 107-135). 

 

Comment 3: More detailed information is needed regarding the specific mechanisms behind defect formation. Additionally, the manuscript should address how these defects affect device performance under various operating conditions.

Response 3: Authors are  grateful for this valuable comment. The comprehensive discussion on defects and their impact on device properties (parameters) has been included in the revised manuscript (Lines 206-232).

 

Comment 4: If there have been significant theoretical developments, these should be included. Adding a section on relevant theoretical investigations would provide a more comprehensive overview and deepen the reader's understanding of the subject.

Response 4: The Reviewer pointed out very important issue. The theoretical studies (simulations) are extremely difficult for ab initio approach; hence, the most evaluations are done using semi-empirical potentials, DFT, etc. Even though these calculations give a hint on defect formation, the calculations still cannot be directly compared with the experimental data. As a result, this review focusses on the experimental evidence to provide reliable data.

 

Comment 5: The conclusions and perspectives section currently provides a simplistic summary of the results discussed earlier. It lacks important insights into future directions and emerging trends. This section should be expanded to highlight significant findings and suggest potential avenues for future research.

Response 5: The authors fully agree with the Reviewer and appropriate discussion on future direction and trends was included in conclusion section of revised manuscript (Lines 483-494)

 

Comment 6: As a review paper, it is crucial to cite more recent references to accurately reflect the latest developments in the field.

Response 6: Revised manuscript cites more and recent references. One quarter of references (in the revised manuscript) is published in the last 3 years. Authors admit they also cite older references; however, it is because authors cite original works since they deserve to be cited.

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript contains the review analysis of experimental  measurements
of activation energy of defects in the three wide band  semiconductors
-SiC, GaN  and  beta-Ga₂O₃. Based on experimental literature data authors are
building two dimensional maps for the activation  energy- capture cross  sections and 
predict trap states in these  materials.

This paper can be published after some corrections.

The three analyzed materials are difficult  to compare side by side as they are very different with the exception that all of them are wide band gap materials. The review does not discuss the crystal  and  electronic structure of these materials. And it seems that what is important for the trap state is not only the activation energy but also the symmetry. The crystal structures assume to be the  hexagonal,  wurtzite, and  monoclinic, respectively. Thus, for  example, the vacancy  surrounding and  defect states are  different  due to hexagonal,  tetrahedral or  monoclinic crystal perturbations. Moreover, Ga₂O₃ is characterized by strong
polymorphism and  when in beta-Ga₂O₃ both  cation  and  anion lattices needs special attention. It seems that there is a need for additional discussion about the type of conductivity in these materials. In particular, it is doubtful to see shallow acceptor states in Ga₂O₃ because there is the flat valence band  maximum.

Moreover, the authors include results for doped and undoped materials in one map. And there it is not clear whether a given trap state is associated  with the native defects or impurity  states.

In Figures 1-3 one can observe  different trend directions on the presented maps. There is a need for thorough discussion for this observation and explanation.

The proposed way with the presenting of maps is interesting, but such maps should be multidimensional rather than two dimensional for the reasons specified above.

 

Author Response

Comment 1: The three analyzed materials are difficult  to compare side by side as they are very different with the exception that all of them are wide band gap materials. The review does not discuss the crystal  and  electronic structure of these materials. And it seems that what is important for the trap state is not only the activation energy but also the symmetry. The crystal structures assume to be the  hexagonal,  wurtzite, and  monoclinic, respectively. Thus, for  example, the vacancy  surrounding and  defect states are  different  due to hexagonal,  tetrahedral or  monoclinic crystal perturbations. Moreover, Ga₂O₃ is characterized by strong
polymorphism and  when in beta-Ga₂O₃ both  cation  and  anion lattices needs special attention. It seems that there is a need for additional discussion about the type of conductivity in these materials. In particular, it is doubtful to see shallow acceptor states in Ga₂O₃ because there is the flat valence band  maximum.

Response 1: The authors are grateful for this comment. The authors agree with the reviewer that all three discussed semiconductors have been envisioned for power electronics applications; however, they differ in all material or electronic properties. Even though the semiconductor materials differ, this review aims to find a common way of trap state evaluation. Appropriate discussion was included in modified manuscript (see Lines 234-255).

 

Comment 2: Moreover, the authors include results for doped and undoped materials in one map. And there it is not clear whether a given trap state is associated  with the native defects or impurity  states.

Response 2: Thank you for your comment. The charge trap maps include native defects as well as impurity-related defects representing intentional or unintentional doping. The graph legend distinguishes these defects; hence, the reader can compare intrinsic and extrinsic defects.

 

Comment 3: In Figures 1-3 one can observe  different trend directions on the presented maps. There is a need for thorough discussion for this observation and explanation. The proposed way with the presenting of maps is interesting, but such maps should be multidimensional rather than two dimensional for the reasons specified above.

Response 3: Authors are thankful for valuable comment. The charge trap distributions in the presented maps are discussed in modified manuscript to provide meaningful discussion, summary, and mutual comparison (Lines 458-482).

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I have no additional comments.