Effect of the Gaseous Atmosphere in GaAs Films Grown by Close-Spaced Vapor Transport Technique

Round  1

Reviewer 1 Report

This manuscript presents the results of some experiments studying the effect of N2 and H2 atmospheres on GaAs film growth by means of CSVT technique. This topic is interesting from the point of view of GaAs film manufacture. The manuscript unfortunately suffers from a number of issues. The authors are kindly requested to take them into account for improving its quality.

Lines 42-44: the abbreviations VGF, VPE and MBE are not necessary, because they are not used elsewhere in the text.

Line 81: “The following reactions were proposed…” Where were they proposed? Please add a reference.

Section 2: A description of the characterization techniques and procedures is missing.

Line 102: Do the films break during deposition or during cooling? What was the cooling rate?

Figure 3a: It would be good to use more contrasting colors.

Figure 3, caption: it sounds like the bandgap determination has been carried out in a hydrogen atmosphere, while the atmosphere is probably referring to the sample growth conditions. Please amend the caption to make things more clear.

Figure 3a and related text. The transmittance values stated in the text for the samples deposited under hydrogen atmosphere do not match those shown in the figure.

Table 1: What is the uncertainty on the thickness values? Please add them in the table.

Lines 146-147: the given values for the composition only concern one sample out of two. Please take an average or also discuss the ratio that is not as good.

Table 2: Please add standard deviation values. Such accurate values are certainly not realistic.

Figure 4 – Table 3 and related text: Has instrumental broadening been taken into account for the particle size calculations? And if yes, how?

Table 3: The caption does not include a description of the last 4 columns. Standard deviations have to be added on all values to help concluding on the significance of the observed differences.

Lines 169-170: It seems that two different samples are referred to as “5-minutes”.

Lines 175-176: Peak shift: How was the sample alignment performed?

Line 179: The FWHM values are not the “crystallinity degree”.

Line 181: “we could not observe photoluminescence”: how were these measurements conducted?

Line 193: “Figure 5 shows a typical Raman spectrum”: In fact there are 4 spectra in that figure.

Lines 203-204: Are the differences in FWHM really significant enough to conclude this?

Figure 5c: Have you considered a contribution of the substrate to the spectrum? This film is thin and maybe not continuous in view of its granular appearance.

Author Response

Good day,

Thanks for your comments. I attach the file with the answers to your observations.

Author Response File: Author Response.docx

Reviewer 2 Report

‍‍The manuscript presents a study of the effect of the gaseous atmosphere in the crystalline quality, surface morphology, and growth rate in GaAs films grown by close-spaced vapor transport (CSVT) technique. Although growing single-crystal GaAs using CVST method is not a new topic, the work is certainly interesting and could be important for the large-scale fabrication of photovoltaic devices, and thus worth publishing in some journals.

In general, the English in the present manuscript is not of publication quality and require major improvement. I have read the manuscript several times, but I am still not quite sure what the authors meant in some sentences/paragraphs.

Some comments:

On Page 3: Line 100-104, the     authors claimed that the atmosphere of H₂ produces a relatively     smooth surface. I would avoid the word smooth, given that with only x 2k     mag we can clearly see a pattern that looks like hexagonal pyramids. It is     homogeneous and (almost) continuous, but it is not smooth.

On Page 3: Line 100-104, the     authors also mentioned that the cracks are due to the layer coming off. I     don’t think that is correct. It is most likely due to strain. The fact     that the crack disappeared with increasing film thickness strongly     suggests that the cause of the crack was indeed strain.   

Generally, increasing deposition time will     increase the cluster size. In the present manuscript, the authors observed     a decrease in the cluster size with increasing deposition time in the case     of films grown in nitrogen atmosphere. Could the authors provide any     explanation or discussion on this?

Fig. 5 (d), there is a feature at low-frequency     shoulder of the TO peak. Is that the As-As vibration mode? Please add this     in the manuscript.

On Page 7: Line 203-205, it is not clear what     the author meant by better crystallinity in the sample of 5 minutes for     the TO mode while for the LO mode the 13-minute sample is better. If the     crystallinity of the sample improved, we should expect a decrease in the     FWHM of both phonon modes. Correct?         

On Page 7: Line 215-218, the authors claimed     that reordering take places in situ for 13-minute film grown in N₂     atmosphere. However, table 3 shows that the FWHM of the TO and LO phonon     modes increases with deposition time, which suggest that the film becomes     more disorder.

The authors observed a very large shift in the     phonon peaks for 5-minute film grown in N₂ atmosphere and     inferred that this behavior due to lattice mismatch/macrostrain. Would it     be possible for the authors to quantify or calculate the strain from the     XRD measurements?    ‍‍

Comments for author File: Comments.pdf

Author Response

Good day,

Thanks for your comments. I attach the file with the answers to your observations.

Best regards

Jesus Bueno

Author Response File: Author Response.docx

Round  2

Reviewer 1 Report

I thank the authors for their efforts aiming at improving their manuscript, which is already looking much better. There are however a few points that are not satisfactory enough yet:

The 6 Angstrom accuracy on the thickness measurements is the absolute uncertainty on the reading as provided by the instrument supplier. In view of the microstructure of the films, the actual standard deviation is certainly higher. Please estimate it and provide this value for each film.

In table 1, there should also be an uncertainty indication on the band gap. In fact, looking at figure 3b, the straight line used for this determination is going through data that are not really linear, so the value cannot be precise to 3 significant figures.

For the grain size calculation, the instrumental broadening must be taken into consideration.

Author Response

Good day,

I attach the manuscript.

Regards!!!

Author Response File: Author Response.docx

Reviewer 2 Report

Thank you for addressing all of my comments. Overall the quality of the manuscript is improved. However, the English is still not of publication quality and requires some text editing.

Author Response

Good day,

I attach the manuscript.

Regards!!!

Author Response File: Author Response.docx

Round  3

Reviewer 1 Report

The last amendments are satisfactory and the new version of the manuscript can be accepted in its present form.