Growth and Optical Properties of Ga₂O₃ Layers of Different Crystalline Modifications

Round 1

Reviewer 1 Report

 In this work, layers of gallium oxide Ga2O3 were grown on silicon substrates with a buffer 11layer of dislocation-free silicon carbide by hydride vapor-phase epitaxy (HVPE). I recommend publishing it after minor revision:

 

1) Please re-check the grammar of the manuscript.

2)The abstract should be expressed more clearly to accurately summarize the main idea of the paper

3)The abstract should be expressed more clearly to accurately summarize the main idea of the paper

Author Response

The authors express their deep gratitude to the reviewers for valuable comments that significantly improved the manuscript. The authors agree with all the comments in accordance with which this article has been corrected. Corrections in the article are highlighted in yellow.

1. Please re-check the grammar of the manuscript

We did our best to correct the grammar.

2. The abstract should be expressed more clearly to accurately summarize the main idea of the paper.

The abstract is completely rewritten, with the main results highlighted more clearly (lines 11-24).

 

Reviewer 2 Report

The article undoubtedly contains some new results that may be recommended for publication, but only after improvement and concretization of some incomprehensible points.

1. One of the main shortcomings of the article is excessive self-citation (10 out of 25 references, which is 40% with a reasonably acceptable 20%).

2. The introduction lacks even a short overview (3-4 sentences) about the latest calculations. See, for example, few very recent papers:

Usseinov, A. et al.   Vacancy Defects in Ga₂O₃: First-Principles Calculations of Electronic Structure. Materials 2021, 14, 7384. https://doi.org/10.3390/ma14237384

Tse, G. 2022. Evaluation of structural, electronic, optical, elastic, and mechanical properties of triclinic Sn-doped Ga2O3 using density functional theory. Computational Condensed Matter 30,e00641 https://doi.org/10.1016/j.cocom.2022.e00641

Usseinov, A., Platonenko, A., Koishybayeva, Z., Akilbekov, A., Zdorovets, M., & Popov, A. I. (2022). Pair vacancy defects in β-Ga2O3 crystal: Ab initio study. Optical Materials: X, 100200. https://doi.org/10.1016/j.omx.2022.100200

3. Comparison of MCSA methods with other recently used will be also important.

4.  Fig.2.  Comparison with other experiments and corresponding supported references must be added to the text.

5. Fig.6 and Fig.7.  How the results obtained agree with others but are calculated using different codes. Comparison with experiments is also important.

6. As for the Raman frequencies, it is recommended to collect all the data in one table and give a clear interpretation with the appropriate

7. In Conclusions (which is absent), it is necessary to clearly articulate what new data have been obtained.

 

In principle, this is a rather interesting topic, which, of course, needs to be developed and promoted, the results obtained are interesting and can be recommended for publication after detailed consideration and disclosure of the above-mentioned ambiguities.

Author Response

The authors express their deep gratitude to the reviewers for valuable comments that significantly improved the manuscript. The authors agree with all the comments in accordance with which this article has been corrected. Corrections in the article are highlighted in yellow.

1. One of the main shortcomings of the article is excessive self-citation (12 out of 25 references, which is 45% with a reasonably acceptable 25%).

We have reduced the number of references to our work to 7. Instead, we used references to theoretical works on point defects in beta-Ga₂O₃ [8-10] and dielectric function [26].

 2. The introduction lacks even a short overview (3-4 sentences) about the latest calculations.

We did it on page 1, lines 41-44, and made 5 new references [7-10, 26].

 3. Comparison of MCSA methods with other recently used will be also important.

We briefly discuss the main differences between the MCSA method and the other methods on page 2, lines 85-91, for which reference is also made to the reviews [12, 13]. 

4.  Comparison with other experiments and corresponding supported references must be added to the text.

The necessary text and reference [13] are provided on page 3, lines 112-114.

 5. Fig. 6 and Fig.7. How the results obtained agree with others but are calculated using different codes. Comparison with experiments is also important.

It is pointed out on page 7, lines 189-192, that the frequencies of the main lines coincide very well with a similar result obtained with the hybrid B3LYP functional [6]; it is very difficult to compare the amplitudes because of the birefringence.

 6. As for the Raman frequencies, it is recommended to collect all the data in one table and give a clear interpretation with the appropriate

The data on the main Raman lines of all three phases are given in a single table in Section 4 (page 14). A discussion of the results recorded in the table is given on pages 13, 14, lines 358-364.

 7. In Conclusions (which is absent), it is necessary to clearly articulate what new data have been obtained.

The conclusion was added on page 15, lines 376-388, where the new results were clearly stated.

Reviewer 3 Report

This manuscript employed the hydride vapor-phase epitaxy method to deposition ?, ?, and ? phases Ga₂O₃ with a buffer layer of SiC on Si. The Ga₂O₃ film was systematically studied by XRD, Raman, and DFT at different deposition temperatures. However, to improve the current manuscript, I believe the following comments should be addressed:

Comments 1): The introduction provides sufficient background. However, references were not cited for lines 40-47. At least 13 of the 25 references are from the corresponding author, Andrey V. Osipov. Why is this work interesting to the public? Please consider adding and comparing more public literature.

Comments 2): Academic writing needs to be precise. In line 22, “the oxygen atom plays here the role of a catalyst for the substitution reaction.” The word “catalyst” may confuse the public. CO and SiO are involved in the reaction in equation 1.

What is the meaning of “и” in line 172? If this is a typo, please correct it. If not, please elaborate.

Comments 3): In lines 50-51, The authors mentioned: “The SiC(111) buffer layer protects silicon from oxidation and significantly improves the orientation of the growing Ga2O3 layers.” Why SiC(111) can significantly improve the orientation of Ga₂O₃? Is it because of the lattice constant? What is the reference?

 

In line 83, why silicon wafers “oriented with a declination of 4^o from the base (111) orientation towards the [110] direction” were used? Is this related to the lattice constant?

Comments 4): There are 21 figures in one article. I strongly suggest the authors merge some figures to improve the readability. For example, merge Figures 1-3 as one figure for the reference sample. In section 3.3, ? phase of Ga₂O₃ was studied by XRD, Raman, and DFT in Figure 16-21. These results can be merged into one figure. The experimental and calculation Raman can be merged into one subfigure. This issue needs to be addressed in other sections too.

Comments 5): The details of DFT calculations (lines 161-169) need to be moved to section 2. Materials and Methods.

Comments 6): The dielectric function results (Figures 9, 15, 21) are shown but not elaborated. Please analyze the results in greater detail.

Author Response

The authors express their deep gratitude to the reviewers for valuable comments that significantly improved the manuscript. The authors agree with all the comments in accordance with which this article has been corrected. Corrections in the article are highlighted in yellow.

• The introduction provides sufficient background. However, references were not cited for lines 40-47. At least 12 of the 25 references are from the corresponding author, A. V. Osipov. Why is this work interesting to the public? Please consider adding and comparing more public literature.

 

The aforementioned text is improved, all necessary references are included, page 2, lines 49-58. We have reduced the number of references to our work to 7. Instead, we used references to theoretical works on point defects in beta-Ga₂O₃ [8-10] and dielectric function [26].

 

• Academic writing needs to be precise. In line 22, “the oxygen atom plays here the role of a catalyst for the substitution reaction.” The word “catalyst” may confuse the public. CO and SiO are involved in the reaction in equation 1. What is the meaning of “и” in line 172? If this is a typo, please correct it. If not, please elaborate.

 

Indeed, although oxygen is part of CO and SiO, it is oxygen that plays the role of a catalyst in the reaction between Si and C to form SiC via the transition Si-O-C state. Without it, this reaction would not take place, which is shown in [15]. The whole text is improved on page 2, lines 77-83. A typo in the caption to Fig. 5 has been corrected.

 

• In lines 50-51, The authors mentioned: “The SiC(111) buffer layer protects silicon from oxidation and significantly improves the orientation of the growing Ga2O3 layers.” Why SiC(111) can significantly improve the orientation of Ga2O3? Is it because of the lattice constant? What is the reference? In line 83, why silicon wafers “oriented with a declination of 4o from the base (111) orientation towards the [110] direction” were used? Is this related to the lattice constant?

Yes, indeed SiC is much better at orienting Ga₂O₃ than Si. This is an experimental fact, reference to the experiment [7]. The present work also proves it (lines 359-366), because we managed to grow 3 high-quality phases at once, whereas it is impossible on silicon. It is very likely that one of the reasons is the oxide layer on Si, which is impossible to get rid of when growing Ga₂O₃ (lines 63-64). Experiment shows that steps on the surface markedly improve the quality of growth of Ga₂O₃, so we used wafers oriented with a declination of 4^o from the base (111) orientation towards the [110] direction.

• There are 21 figures in one article. I strongly suggest the authors merge some figures to improve the readability. For example, merge Figures 1-3 as one figure for the reference sample. In section 3.3, ? phase of Ga2O3 was studied by XRD, Raman, and DFT in Figure 16-21. These results can be merged into one figure. The experimental and calculation Raman can be merged into one subfigure. This issue needs to be addressed in other sections too.

To be honest, it seems impossible to combine 6 pictures into 1, because it would be impossible to read anything on them. Therefore, we merged 8 figures into 4 and reduced the number of Figures to 17.

• The details of DFT calculations (lines 161-169) need to be moved to section 2. Materials and Methods.

 

Done (lines 144-152).

 

• The dielectric function results (Figures 9, 15, 21) are shown but not elaborated. Please analyze the results in greater detail.

The dielectric function results are discussed on page 14, lines 341-349. It is pointed out that while there are very few experimental data on the dielectric function for the β phase and the ε phase (which, apparently, can be explained by the roughness of these phases), there are such data on the α phase. In particular, in the work [29] such a spectrum was measured on the synchrotron ellipsometer in the MLS, Berlin in the region from 0.04 to 20 eV. The agreement of the data obtained in the present work with the data [29] is very good, despite the significant difference in the growth technique of Ga2O3. The method used was ultrasonic mist chemical vapor epitaxy on (0001) α- Al2O3 substrate.

Round 2

Reviewer 2 Report

The  authors have successfully improved their original manuscript, which can now be recommended for publication.

Reviewer 3 Report

The authors have addressed the comments. I agree to accept this version of the manuscript.