Design of High-Power Red VCSEL on a Removable Substrate
Round 1
Reviewer 1 Report
The authors made a good summary of the development of red VCSEL and the theory of designing it in this paper, and realized a high power VCSEL with removable substrate. But in the context, I didn’t find strong evidence that supporting the originality and novelty of the research stated here. So I think it is not suitable for publication at its current stage.
Author Response
Thank you for your review and suggestion.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The paper deals with AlGaInP/InGaP VCSELs for 680 nm emission design and simulation. It begins with a thorough but concise review of diode laser history, describes the design and simulation procedures, and continues to elaborate on the results and reasoning of each step.
This kind of structure, with easy to read but quite long-form writing leads to a long paper. As a tutorial/review paper I found that this would be useful for a number of early stage researchers in the field.
Although the procedures are clearly detailed by a plethora of equations, I didn't come across a mention of the used software (or reference) to the used drift-diffusion solvers for solving band structure and LIV curves. Same applies for the thermal simulations. Those could be valuable additions to the text. It was pleasant to see the used epitaxial structure given as an appendix.
There were some grammatical issues or non-typical expressions used. Without elaborating too much, please take a look at the following lines:
32
33
39-40
108 (manipulated -> operated?; established -> realized/fabricated?)
129 (missing ref.)
211
253 (Maybe it would be clearer to use different terms here, e.g. electrons leaking from n-side to the p-side?)
Other comments:
73-74: Maybe more quantitative analysis is needed to end up with this argument?
150-151: This doesn't apply generally, especially in surface emitting lasers where mode intensity is a periodic function.
Author Response
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Author Response File: 
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Reviewer 3 Report
The paper is on an interesting subject, but unfortunately the model used, as described (it is possible that the description is not accurate and the actual model was more detailed) is far too simplistic for the results to be trustworthy. Specifically:
1) Eq. (5) holds in practice only for very deep wells. The well for electrons in red laser materials is not very deep, so any result obtained with this equation will be very inaccurate. For holes, it will be probably OK, but not for electrons.
2) Eq. (14) is for a bulk material, not for a Quantum Well. The matrix element Ep/3 does not apply in Quantum Wells, and it is important to treat the reduced density of states carefully, taking into account different levels, light and heavy holes, etc. Perhaps this has been done, but from the equation it is not clear.
The model should also include linewidth broadening (which, from Fig 5, seems to have been taken into account - then what is the meaning of eq. 14?) and possibly bandgap shrinkage (though there are different views on the latter).
There are also a number of language and presentation flaws, e.g. eq. (4) describes the highest supported energy level or the number of supported levels; the gain in Eq. (14) is not quite material gain (material gain is a function of material only so does not contain the confinement factor), etc.
Author Response
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Reviewer 4 Report
In the paper Design of high-power red VCSEL on a removable substrate authors presented detailed analysis of the influence of InAlGaP/InGaP barrier/QW parameters on the properties of red emitting VCSEL. Paper is well organized and easy to follow. In my opinion is almost ready for publication. I suggest to make same small corrections listed below:
- lack of superscripts: lines 64, 428
- lack of reference in line 53?
- lines 61, 65 please include references into the sentence
- Please place the figures jus after first mention in the text, not first figure than mention in the main text
- line 264 - I would recommend to write p-DBR and n-DBR instead of P-DBR and N-DBR. It could be confusing and may suggest that DBR are doped with phosphorus and nitrogen
- line 272 and equation 22 - ND usually stands for donor concentration. When talking about electrons I would recommend to use n
- which software was used for calculations described within the paper?
- what is the minimum substrate thickness accessible by substrate removal?
Author Response
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Round 2
Reviewer 1 Report
As explained by the authors, they indeed did detailed research work and presented in the manuscript. The content of the paper really could be a fine guide for new researchers starting their analysis and experiments in this field. But as the authors wanted to propose their research work as a guide, they should prepare their analysis more rigorously. Like in equation (23), the power injected into the VCSEL is not all consumed for generating heat. The output light power is also generated from the power consumed by the VCSEL. There is no voltage information in the paper. And the authors didn't clarify the information how many power injected and what percentage within it is for generating output light. On the other hand, substrate removal process is a mature technology for flip-chip packaged VCSEL. Many research work for 850nm VCSEL had been done. So that, the authors statement "However, since the GaAs absorption wavelength contains 404 red wavelengths, red VCSELs are not suitable for bottom -emitting processes" is not quite rigorous.
Author Response
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Reviewer 3 Report
The paper has improved, but the description of the gain still needs some clarification - please write out explicitly the expression for multiple bands involved, the account for linewidth broadening, and give a reference to where the matrix element expressions were taken from (e.g. whether the valence subband mixing was taken into account).
Author Response
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Round 3
Reviewer 1 Report
Thanks for the authors efforts, there is only a minor correction should be made.
The power consumed for generating heat had been changed by removing the part converting to output light. It would result in the changes of thermal resistance. The authors should take this in consideration and recalculate the thermal resistance data and correct Fig. 8
Author Response
Thanks for your suggestion. We are sorry for the misunderstandings caused by the first version of the manuscript. The calculation of thermal resistance takes into account the difference between optical power and electrical power from the beginning, which has been presented by equation (26). Therefore, Figure 8 does not require additional corrections.
