Enhanced Performance of High-Power InAs/GaAs Quantum Dot Lasers Through Indium Flushing

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper introduced the indium flushing of the InAs/GaAs laser, which slightly improved the laser's performance. Indium flushing for QD lasers is a known method for improving laser performance, which has been discussed in detail elsewhere. Several issues need to be addressed before I can reach a decision.  

1-     The Authors didn’t state clearly the novelty of this work. Several other publications investigated the indium flushing of the QD lasers [1]. Please discuss in detail in the introduction, why this work is different from the other works published before.

2-     The improvement in the performance is slight. Statistics should be made, such as stating how many samples you tried and the standard deviation and error bars of each measurement, to be able to judge if the reported improvement is not within the uncertainty limits of the measurements themselves.

3-     AFM image in Fig. 2 doesn’t show any information about particle size distribution, please add a graph to show that to be clear what is the improvement after the flushing.

4-     What is the single/multi longitudinal and spatial mode operation behaviour of the laser before and after applying the flushing?

5-     What are the reasons that there is no significant improvement in the emission linewidth compared for example to the improvement in [1].

6-     There are a few other minor mistakes, typos, and not enough information provided such as (just examples):

-Temperature unit stated in Fig 3, 4

- In Fig. 5 a and b there is no sufficient information about color meaning and attached numbers in the P-I curves

Please revise the manuscript for such mistakes

Comments on the Quality of English Language

 There are a few other minor mistakes, typos, and not enough information provided such as (just examples):

-Temperature unit stated in Fig 3, 4

- In Fig. 5 a and b there is no sufficient information about color meaning and attached numbers in the P-I curves

Please revise the manuscript for such mistakes

 

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

In the present paper, the authors investigate the performance enhancement of high-power InAs/GaAs quantum dots laser utilizing indium flushing. The authors also compare the flushed and unflushed samples regarding threshold current, power, and temperature stability. The topic in the manuscript is sound and of interest to a wider physical community. The paper is well prepared and the study in the paper corresponds to a very active research area. I expect that the paper will be accepted for publication after minor revisions. I would suggest the authors address the following points: 

1. Some abbreviations first mentioned in the abstract should be given their full names.

For instance, quantum dots (QD),  photoluminescence (PL);

2. To make the readers better understand the background, physical meaning, and motivation of the investigation, the part of the introduction in the paper should be divided into several small paragraphs. 

3. I believe the authors are missing some important references relevant to the study in the manuscript.

I can recommend the paper to be published in Photonics after the authors have considered these items.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This paper describes effects of the In-flushing process during the MBE growth of a quantum dot (QD) laser structure. They concluded that the In flush provides higher QD density with lower size variation, better (stronger, narrower) QD photoluminescence, lower laser threshold current, smaller current dependences of both the emission energy  and FWHM, and higher temperature stabilities in both the threshold current and emission efficiency. The experimental data are mostly clear except the temperature stability data. The topic looks suitable for the publication in this journal, but there are a few points which have to be reconsidered or revised before the final decision for publication as suggested below.

 

1.    The description on the growth sequence including the detailed process of In flush should be clearly given. The present description of the growth (p.2, line 54-67) does not correspond to Fig.1. Where are 30nm buffer and 40nm spacer? What procedure is taken exactly in the In flush process? Please give complete description of the every detail of the growth step maintaining the correspondence with Fig.1.

2.    What physical effect is expected and has been experimentally observed by introducing the In flush process has not been explained fully in the text. This should discussed by referring appropriate references.

3.    P.3, l.107: Please include info on the facet coating.

4.    P.6, l.176: Please give the definition of the parameter Ti. If this is expressed by a relation similar with that used for To, please explain physical basis of the definition, together with appropriate references, if any. The present reviewer doubts if the slope efficiency is described by a relation same as that for To.

5.    In Fig.5(a), L-I characteristics of flushed QD laser above 50 ℃ show abnormal behavior, giving saturating threshold current as shown in Fig.5(b). The saturating behavior seems not to be justified by using an ordinary physical model, and the determination of To=1436K looks to be abnormally large and probably erroneous. Please explain such anomaly in the L-I characteristics of flushed laser. The conclusion and abstract should be revised accordingly. As for the value of To below 50 ℃ in the flushed laser (To=64K) is smaller than that for unflushed laser (141K). This seems to show a drawback of introducing the In flush process.  The authors may have to reconsider the temperature range for To determination, and are recommended to discuss physical reason of To decrease in In flushed lasers. In addition, how are those To values compared with literature values reported on QD lasers? Such discussion should be useful for readers’ correct understanding of the In flush effect.

6.    Minor corrections are recommended to be made:

P.5, l.144: -- with [less] carrier leakage or thermal escape than [in] QD ---

P.6, l.170: --- than [in] a flushed sample.

P.6, l.173:  ---[for] the flushed sample.

Other similar corrections may be required in the text. Please check English carefully.

P.6, Fig.5 (c) and (d): Temperature unit [ (℃)] is not printed properly.

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

The manuscript by Deyan Dai and co-authors is devoted to the experimental study of MBE-grown InAs/GaAs quantum dot lasers. In particular, it is shown that indium flushing applied to the grown structures allows to enhance the performance of these lasers: decrease the threshold currents, increase the outpur power and obtain better temperature stability. The paper is well-written and can be of interest for the semiconductor laser community. I'd like to recommend its publication after the authors consider several minor comments:

 

1) The authors estimate and discuss the characteristic temperature T0 of their samples, but do not define it. Why does it not depend on the ambient temperature?

 

2) The question marks appear in Fig. 5 instead of K.

 

3) Figure 1 contains two almost identical panels. Additional explanations are needed on the difference between them.

 

4) The list of authors in Ref. 5 should be corrected.

 

5) The term "zero-dimensional" used by the authors with respect to quantum dots is not the best choice. Zero-dimensional interpretation can be applied in some theoretical studies. On the contrary, the nanocrystals grown by the authors have clearly finite dimensions. By the way, what is the size of the quantum dots grown here?

Author Response

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Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I know that there are a lot of efforts made by the authors to get this work done in its shape. But I'm not yet convinced that the quality of the results and the achieved improvement are fit in publication in its current form. Therefore, I may recommend the following to the authors: 

1- make the necessary optimization in the flush procedure (pressure, duration, etc) to have a significant improvement in the performance. Maybe also apply any wavelength selective methods as in other papers to have a single-mode operation, which may lead to a better demonstration of the improvement. 

or (but I do not prefer)

2- Do the same tests on other different new diodes to ensure that the slight improvements are real and caused by flushing not any other factors like the measurement errors. 

 

In addition, the introduction still didn't show the advantages and the novelty of the work from other works. Please include what you have mentioned in the review report in the introduction (after better explanation and more details to suit readers from different backgrounds)

 

Comments on the Quality of English Language

more relevant things at the moment need to be considered

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have responded sufficiently to most of the reviewer’s comments. However, some pieces of information, which the authors have provided in the response letter to the reviewer #3’s comments and seem to be useful for readers, have not been reflected in the main text. The authors are recommended to make minor revision to finalize the manuscript by considering the following comments:

 

1.    The reviewer #3’s previous Comment 1:

“our previous work(Chinese Physics B 32 (2023): 98103-098103)” should be included in the references. Also some information on the “In desorption point” (such as “20-25 deg higher than the QD formation temperature”) should be included in the text, since this may be useful for readers.

2.    Comment 4:

To the present reviewer, the definition of Ti looks still not backed up by rigid theory, which is reasonable because those parameters can be influenced by too many laser/material parameters. The authors are recommended to use T0 and T1 as “empirical” or “phenomenological” parameter as used in previous works. Definition equation can be shown, or at least references such as (https://doi.org/10.1016/j.optlastec.2019.106019) and (https://doi.org/10.1063/5.0096367) as mentioned in the response letter should be shown (probably at L.181).

3.    Comment 5:

Revised text is better than previous text. But, the expressions on L.185 (comparable) and on L.186 (superior) are inconsistent. This can be solved by removing “superior”.

4.    Other minor corrections:

L.173: apparently→apparent

L.175:performances→performance

L.182:picture 5c→Fig. 5(c)

Fig. 5(a) and (b): vertical axis parameters with units are missing

L.183: is → =

L.185: for → with that of

L.194: For another, → delete

Please check again detail of English presentations.

Author Response

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Author Response File: Author Response.pdf