Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1. The simulation assumes a Schottky gate with a fixed work function, but practical device performance is often influenced by the gate dielectric's band alignment with the barrier layer. Experimental work on PEALD-grown AlNO on AlGaN/GaN has demonstrated that precise determination of band offsets using angle-resolved XPS is critical for understanding gate leakage and threshold voltage behavior. For κ-Ga2O3/GaN HEMTs, similar experimental validation of band alignment at the gate interface would strengthen the credibility of the simulated threshold voltage trends.
2. While the introduction of a p-GaN cap layer enables normally-off operation, the manuscript does not discuss the possible role of surface or interfacial layers in modulating the threshold voltage.
3. The manuscript highlights the ultrahigh 2DEG density in κ-Ga2O3/GaN HEMTs but does not sufficiently address the potential impact of interface traps or dielectric quality on electron mobility. Recent studies on AlGaN/GaN heterostructures have shown that nanolaminate films, such as HfO2/La2O3grown by plasma-enhanced atomic layer deposition, can effectively passivate surface states and improve carrier transport properties (Rsc Advances 2014, 4 (69), 36828). A similar approach could be considered to further enhance the mobility and reduce current collapse in κ-Ga2O3/GaN devices. The authors may benefit from examining such interface engineering strategies or at least make a comment.
4. The simulation results are promising, but the lack of experimental benchmarking limits the impact. The authors are encouraged to compare their simulated electrical performance (e.g., SS, ION/IOFF, Vth) with experimental data from similar heterostructures. For instance, studies on AlGaN/GaN with advanced gate stacks have used angle-resolved XPS to correlate band alignment with device characteristics(Applied Surface Science 2017, 423, 675-679). A analogous experimental validation for κ-Ga2O3/GaN, particularly regarding the effect of the p-GaN cap on band bending, would greatly enhance the practical relevance of this work. If further experiments are limited, the comments on previous techniques are necessary.

Author Response

We would like to express our sincere gratitude to you for your time and effort in reviewing our manuscript. Their constructive feedback has been invaluable in helping us improve the quality of our paper. Please find our point-by-point response in the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The authors discuss the performance of k-Ga2O3/GaN HEMTs based on theoretical TCAD simulations. The overall logic and structure of the manuscript are generally acceptable; however, several concerns should be addressed before publication.

1. In the Introduction, the authors discuss the suitability of k-Ga2O3 for k-Ga2O3/GaN HEMTs due to its theoretically high spontaneous polarization coefficient. The manuscript then states that “Experiments also observed the presence of a 2DEG; however, its concentration is lower than theoretical predictions, likely due to the existence of defects.” However, no further discussion regarding these defects or their impact is provided, and the manuscript directly transitions to the main topic with “despite...”. This transition appears abrupt and lacks sufficient logical connection. The Introduction should be further refined to improve the flow and motivation of the study.
2. In Fig. 1, there are noticeable red wavy markings in the GaN region of the figure. Please carefully check and revise the image quality.
3. The reason for choosing Al = 0.3 in the AlGaN/GaN HEMT comparison with the k-Ga2O3/GaN HEMT is unclear. Additional justification for this parameter selection should be provided.
4. In Fig. 3, there is an obvious difference in the reverse leakage current between the two HEMT structures. Is this behavior related to the difference in 2DEG density? Further discussion is recommended.
5. To accurately obtain the band structure of the HEMTs, the carrier concentration and doping parameters of each layer are essential. It is recommended that the authors provide the detailed simulation parameters used in the band structure calculations.
6. The authors claim that a k-Ga2O3 thickness of 40 nm results in the highest 2DEG density based on simulation results. However, it is unclear whether the 2DEG density decreases when the thickness is further increased, and if so, what the dominant physical mechanism is. The discussion in this section should be strengthened.
7. In the discussion of the p-GaN cap layer effect, the authors selected a 3 nm k-Ga2O3 layer thickness. The rationale for choosing this value is unclear, especially since it generally corresponds to a relatively low 2DEG density. If a thicker k-Ga2O3 layer (e.g., 25 nm) is adopted, would the application of the p-GaN cap become less effective for achieving normally-off operation due to an excessively negative threshold voltage? Additional discussion is needed.
8. The manuscript lacks discussion regarding carrier mobility, which is another critical parameter for HEMT performance. The authors are encouraged to include discussion on mobility-related considerations. In addition, some discussion regarding practical device fabrication challenges and strategies for improving actual device performance would further enhance the significance of this work.

Author Response

We would like to express our sincere gratitude to you for your time and effort in reviewing our manuscript. Their constructive feedback has been invaluable in helping us improve the quality of our paper. Please find our point-by-point response in the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I suggest to accept this manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have addressed my concerns. I believe the manuscript is now suitable for acceptance.