Growth of Ultrathin Al2O3 Films on n-InP Substrates as Insulating Layers by RF Magnetron Sputtering and Study on the Optical and Dielectric Properties
Round 1
Reviewer 1 Report
To put it short, the manuscript reports an attempt to deposit Al2O3 film (under a single set of deposition conditions - the only varied parameter was deposition time). The results basically show that the attempt was unsuccessful. For example, the transmittance shows an optical band gap of 3.7 eV ... as the authors correctly point out, that of Al2O3 is some 9 eV, i.e they prepared low-quality AlOx rather than high-quality Al2O3.
Let alone statements which make little sense to me, e.g. Al content at specific locations is as low as 1.34-3.88 at.% according to Fig. 4e. (Which element is supposed to constitute the remaining >96 at.%? Oxygen? According to analyses reported elsewhere in the manuscript, namely XPS and transmittance, the overall Al content is well above 40 at.%.)
The motivation in the Introduction is also not fully clear. For example, the statement "No doubt that the atomic-layer deposition is a prevailing technique for ultrathin film preparation with control of the thickness and the composition of the film at the atomic level [10]" may be correct, but it is based on Ref. 10 ("Atomic layer deposition: An overview") which does not constitute anything like comparison of different deposition techniques of Al2O3. So yes, there is a doubt. The mere fact that the authors used reactive magnetron sputtering for Al2O3 preparation is in itself far from new (random examples out of hundreds papers doi.org/10.1016/j.tsf.2007.07.135, doi.org/10.1116/1.580434, doi.org/10.1016/j.tsf.2012.03.113, etc.).
Author Response
Response to Reviewer 1 Comments
Comment 1: To put it short, the manuscript reports an attempt to deposit Al2O3 film (under a single set of deposition conditions - the only varied parameter was deposition time). The results basically show that the attempt was unsuccessful. For example, the transmittance shows an optical band gap of 3.7 eV. as the authors correctly point out, that of Al2O3 is some 9 eV, i.e they prepared low-quality AlOx rather than high-quality Al2O3.
Response: Thanks for your careful review. Yes. Here we report an explorative study that ultrathin aluminum oxide films were attempted to be fabricated on n-InP substrates by RF magnetron sputtering as candidate insulating layers in InP semiconductor lasers for optical communication. Requirements on these Al2O3 films are high-transmittance and low-absorption at 1550 nm (one important atmospheric window for optical communication), and good dielectric properties. Though now there's plenty of room to improve the optical and dielectric properties of the fabricated ultrathin Al2O3 film by RF magnetron sputtering, this exploration still provides valuable references for ultrathin Al2O3 films applied in semiconductor lasers as candidate insulating layers, to reduce the device fabrication cost and simplify the fabrication process.
Comment 2: Let alone statements which make little sense to me, e.g. Al content at specific locations is as low as 1.34-3.88 at.% according to Fig. 4e. (Which element is supposed to constitute the remaining >96 at.%? Oxygen? According to analyses reported elsewhere in the manuscript, namely XPS and transmittance, the overall Al content is well above 40 at.%.)
Response: We truly understand your concern. Actually, the upper Al2O3 film was ultrathin and not even continuous, when the deposition duration was 20 min. So when the 20 min-deposited sample was under EDS test, intense peaks of the substrate elements (In and P ) would dominate and the Al peak was weak. But great differences of the Al content between the islands and the relatively flat areas on the sample were noticed during the EDS test in spot-sweeping mode. Hence, the EDS test results were listed in the manuscript to qualitatively interpret the initial island growth mode of the Al2O3 film.
Comment 3: The motivation in the Introduction is also not fully clear. For example, the statement "No doubt that the atomic-layer deposition is a prevailing technique for ultrathin film preparation with control of the thickness and the composition of the film at the atomic level [10]" may be correct, but it is based on Ref. 10 ("Atomic layer deposition: An overview") which does not constitute anything like comparison of different deposition techniques of Al2O3. So yes, there is a doubt. The mere fact that the authors used reactive magnetron sputtering for Al2O3 preparation is in itself far from new (random examples out of hundreds papers doi.org/10.1016/j.tsf.2007.07.135, doi.org/10.1116/1.580434, doi.org/10.1016/j.tsf.2012.03.113, etc.).
Response: Thanks for your critical comment. Now the Introduction has been reworded and marked in red in the manuscript. It is true that using reactive magnetron sputtering for Al2O3 preparation is far from new. But attempts to prepare ultrathin Al2O3 films (the maximum 40 nm) by magnetron sputtering and to be used as candidate insulating layers in semiconductor lasers for optical communication are still very rare.
Reviewer 2 Report
In present paper the ultrathin alumina films with various thicknesses were obtained by magnetron spattering on n-InP and SiO2 substrates. It has been shown that Al2O3 films amorphous and near stoichiometric. The authors demonstrated two films growth mechanisms on n-InP substrate depend on substrate wettability: island and layer-by-layer. The optical and dielectric properties were discussed in detail. Nevertheless, there are several points before the paper can be published. I hope that authors after revision can improve the paper and can published it in Coatings Journal.
1. In introduction part authors must explain in details why they chose these objects – aluminum oxide. Why they deal with magnetron sputtering, its advantages. Now the introduction part seems poor. I think it would be better if authors broadening it by adding new results. I propose them use following papers which concerned with these problems:
- Shimanovich, D.L. Preparation and morphology-dependent wettability of porous alumina membranes / Beilstein Journal of Nanotechnology, 2018, №9, pp. 1423-1436. (doi:10.3762/bjnano.9.135).
- Tishkevich, D.I. Template Assisted Ni Nanowires Fabrication / Materials Science Forum, 2019, Vol. 946, pp. 235-241 (https://doi.org/10.4028/www.scientific.net/MSF.946.235).
- Vorobjova, A.I. Properties of Ni and Ni-Fe nanowires electrochemically deposited into a porous alumina template / Beilstein Journal of Nanotechnology, 2016, №7, pp. 1709-1717.( DOI: 10.3762/BJNANO.7.163).
2. The text should be carefully checked, some of the wrong spelling are below:
line 21: 3.0x104 cm-1;
line 22: 5x1010 Ω∙cm;
line 29: 107 V/cm;
line 33, 70: Al2O3;
line 56: 7.00x1017 cm-3 and etc.
3. In this form the article looks like an experimental report, more theoretical discussion is expected in the discussion part.
4. I think it will be better to make more recommendations for practical applications.
5. Conclusion must be re-written more widely. Now it seems poor.
6. Authors must improve language. There are some insufficient typos and mistakes in the text.
Author Response
Response to Reviewer 2 Comments
Comment 1: In introduction part authors must explain in details why they chose these objects – aluminum oxide. Why they deal with magnetron sputtering, its advantages. Now the introduction part seems poor. I think it would be better if authors broadening it by adding new results. I propose them use following papers which concerned with these problems:
- Shimanovich, D.L. Preparation and morphology-dependent wettability of porous alumina membranes / Beilstein Journal of Nanotechnology, 2018, №9, pp. 1423-1436. (doi:10.3762/bjnano.9.135).
- Tishkevich, D.I. Template Assisted Ni Nanowires Fabrication / Materials Science Forum, 2019, Vol. 946, pp. 235-241 (https://doi.org/10.4028/www.scientific.net/MSF.946.235).
- Vorobjova, A.I. Properties of Ni and Ni-Fe nanowires electrochemically deposited into a porous alumina template / Beilstein Journal of Nanotechnology, 2016, №7, pp. 1709-1717.( DOI: 10.3762/BJNANO.7.163).
Response: Thanks very much for your patient work and critical comment. Now the Introduction has been reworded and marked in red in the manuscript. Though the atomic-layer deposition is now a prevailing technique for ultrathin film preparation, however the ultimate challenge, i.e., its commercial realization, has been waited for ever since because of its extremely complex process procedures and low deposition rate. Alternatively, sputtering was put forward to meet this requirement, and it has been identified to be a method quite suitable for manufacturing. Hence, here we report an explorative study that ultrathin aluminum oxide films were attempted to be fabricated on n-InP substrates by RF magnetron sputtering as candidate insulating layers in semiconductor lasers for optical communication. As you proposed, new results have been added in the introduction part, as new references [1] and [14].
Comment 2: The text should be carefully checked, some of the wrong spelling are below: line 21: 3.0x104 cm-1;
line 22: 5x1010 Ω∙cm;
line 29: 107 V/cm;
line 33, 70: Al2O3;
line 56: 7.00x1017 cm-3 and etc.
Response: Thanks for your careful review. Sorry for our mistakes. Now, the text has been doubly checked both by ourselves and the other expert.
Comment 3: In this form the article looks like an experimental report, more theoretical discussion is expected in the discussion part.
Response: Thanks for your critical comment. Now more theoretical discussions have been added in the discussion part, like the non-spontaneous nucleation theory to interpret the film growth mode, which have been marked in red in the manuscript.
Comment 4: I think it will be better to make more recommendations for practical applications.
Response: Thanks for this critical comment. Now Abstract, Introduction and Conclusion of the manuscript have all been reworded to point out the potential application of this fabricated ultrathin Al2O3 film as an insulating layer in a InP semiconductor laser for optical communication.
Comment 5: Conclusion must be re-written more widely. Now it seems poor.
Response: Thanks for your careful work. As suggested, Conclusion of the manuscript has been reworded, which has been marked in red in the manuscript. We hope now it is satisfying.
Comment 6: Authors must improve language. There are some insufficient typos and mistakes in the text.
Response: Thanks for your suggestion. Sorry for this mistake. Now, the text has been doubly checked both by ourselves and the other expert.
Reviewer 3 Report
This is an interesting paper on which the authors attempt to coat surface of different materials (n-InP and glass) with thin layer of aluminum oxide. Al2O3 thin films are normally deposited with ALD, CVD or electron/plasma sputtering techniques, while this study explores the possibility of using RF magnetron sputtering for thin film deposition of Al2O3. Furthermore, the authors investigate the electrical breakdown and optical properties of the deposited insulating Al2O3 layer. The paper is well written and the methods are well described. I therefore favor publication in Coatings, provided the authors address the following minor points:
a) Please address recent trends in the fabrication of thin films of highly insulating materials and their applications, such as SiO2: Thin nanoporous metal–insulator–metal membranes, ACS applied materials & interfaces 8 (7), 4292-429
b) Please provide a reference for the XPS data of Al 2P in Al2O3
c) Figure captions should clearly indicate the substrate material.
Author Response
Comment: This is an interesting paper on which the authors attempt to coat surface of different materials (n-InP and glass) with thin layer of aluminium oxide. Al2O3 thin films are normally deposited with ALD, CVD or electron/plasma sputtering techniques, while this study explores the possibility of using RF magnetron sputtering for thin film deposition of Al2O3. Furthermore, the authors investigate the electrical breakdown and optical properties of the deposited insulating Al2O3 layer. The paper is well written and the methods are well described. I therefore favor publication in Coatings, provided the authors address the following minor points:
Response: Thank you very much for your careful work and positive comments about our manuscript.
Comment 1: Please address recent trends in the fabrication of thin films of highly insulating materials and their applications, such as SiO2: Thin nanoporous metal–insulator–metal membranes, ACS applied materials & interfaces 8 (7), 4292-429
Response: Thanks for this critical comment. As suggested, recent trends in the fabrication of thin films of highly insulating materials and their applications has been added in the introduction part, as Reference [2].
Comment 2: Please provide a reference for the XPS data of Al 2P in Al2O3
Response: Thanks for your careful review. A reference for the XPS data of Al 2P in Al2O3 has been provided as Reference [19].
Comment 3: Figure captions should clearly indicate the substrate material.
Response: We sincerely appreciate your careful and patient work. Sorry for our mistakes. Now, all the figure captions have been doubly checked where the substrate material has been clearly pointed out and marked in red in the manuscript.
Round 2
Reviewer 1 Report
I have rejected the original manuscript, and the authors did not really disprove my main arguments. It is perfectly OK that they do research in this field, but contrary to the authors I still think that the results (result of the first attempt) are not yet good and interesting enough to justify publicationin a high-quality journal. I stay behind my original comments and original recommendation.
Author Response
Thanks for your critical comments on the original manuscript. Under your guiding comments, the Introduction has been reworded and the manuscript has been greatly improved. It is true that using reactive magnetron sputtering for Al2O3 preparation is far from new. But our work explored the possibility of using RF magnetron sputtering for ultrathin film deposition of Al2O3, as a candidate insulating layer in semiconductor lasers for optical communication. Results in this work provide good references in reducing the device fabrication cost and simplify the fabrication process.
Reviewer 2 Report
Paper can be published
Author Response
Response：Thank you so much for your careful and patient work.
