Independently Accessible Dual-Band Barrier Infrared Detector Using Type-II Superlattices
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis paper reports the modeling of a novel dual-band T2SL barrier infrared detector (DBIRD). The study is well conducted, the equations are well described, the paper is very well written with a full list of parameters used and references on the subject. This pedagogical work is interesting for the IR community.
Minor additions are necessary to improve the scientific quality of the paper.
- First of all, there are two types of T2SL : Ga-containing InAs/GaSb and Ga-free InAs/InAsSb. The paper is focused on Ga-containing T2SL and this should be clearly stated in the abstract and keywords.
- Conduction and valence band offset (CBO and VBO) are crucial quantities for designing a barrier detector. Defining them from the electron affinity calculated from VBO relative to InSb is not so easy to understand and visualize. It would be useful to report some quantities in the calculated band diagram of Fig. 5a.
- The results on dark current are given at a reverse bias of V = -0.2V and compared to the state of the art. Spectral QE, responsivity and detectivity are plotted from the photocurrent density at -0.2V reverse bias. This reverse voltage should be indicated in the figures or the caption of Fig. 7 and the authors should justify this choice of reverse bias value.
- please, confirm eq. 15 on specific detectivity D*
- MLs has to be defined, first in page 3.
Author Response
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We attach our response to the Review Report 1.
Thank you.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThis manuscript reports a strained layer superlattice (SLS) dual-band infrared (MWIR/LWIR) detector design with the emphasis on the theoretical modeling and simulations. SLS is a fairly matured infrared material system and it is of high interest to the infrared community. The paper is well written and the technical content will be beneficial for the readers. However, I have a list of comments and I recommend the authors to address them in a revised manuscript.
1. Dual-band barrier infrared detector (DBIRD) designs have been studied and reported extensively in the literature. As also mentioned in this manuscript, NBn and n-i-p-p-i-n are the existing designs, which have been demonstrated experimentally both at single element and array levels. Compared to those designs, it is not clear to me what additional benefits the design reported in the manuscript offers. Please add a brief explanation.
2. Authors report that their design is novel. I believe that dual band designs with similar architectures have been already reported. Please specify what is the novelty is.
3. Authors have discussed the details of the growth and fabrication, indicating that this design is feasible to grow, which is great. However, the fabrication of a three terminal device is extremely challenging. Also, the total etch depth is about 9um, which requires advance fabrication processes. It would be beneficial for the readers if the authors specify some applications of simultaneous detection of light in both blue band and red band.
4. The LWIR band has a cutoff of 8.05um, which is very close to the lower bound of the LWIR band. What is the significance of limiting the LWIR band to 8.05um? The RC is in the atmospheric absorption band.
5. A major concern I have is related to the relatively low QE for the BC. As the authors report, the estimated hole diffusion length for the BCA is approximately 5.4 μm and the absorption length of in-band photon is about 3.3 μm. Based on this, I would expect higher than 27-33% QE for the blue channel. Please verify.
6. Also, the authors report that the lower QE for the BC compared to RC is due to the BCA’s low absorption coefficient. This statement is incorrect. Fig. 4 shows that BCA has higher absorption coefficient than RCA. In addition, BCA (5um) is thicker than RCA (3um). Therefore, I would expect significantly higher QE for the BC than RC. There is a clear discrepancy here and please address it.
7. Authors have reported the hole mobility (450 cm2/V s) and the hole lifetime (100 ns) for BCA. What are the numbers for the red channel?
8. What is the intensity of the light used for the calculation of the photocurrent in Figure 6? Or, the authors can report the corresponding blackbody temperature, optics, etc.
Author Response
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Thank you.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe manuscript reports a so-called dual-band barrier infrared detector (DBIRD) using Type-II superlattices. The authors did a theoretical analysis of the optical and electrical performance of the detector. There have been a lot of studies and demonstration of dual-band infrared detector based on Type-II superlattice materials. Different kinds of structures, including nBn、pBp、p-i-n-i-p and barrier structures have been studied (ref. Appl. Phys. Lett. 102, 011108 (2013); Infrared Physics & Technology 86 (2017) 159–164; J. Appl. Phys. 111, 073107 (2012)). We couldn’t find nothing new and innovative in the submitted manuscript. It is not suitable for publication in Photonics.
Comments on the Quality of English LanguageThe quality of English Language is fine.
Author Response
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Reviewer 4 Report
Comments and Suggestions for AuthorsIn this manuscript, the authors demonstrated a novel dual-band barrier infrared detector design (DBIRD) using type-II superlattices. The simulation results predict that the DBIRD will produce low dark currents and 27-33% quantum efficiencies for the blue channel with λc=5.58 µm, 33% for the red channel with λc=8.05 µm. The DBIRD may provide a significantly improved capability and operational flexibility for high-speed dual-band imaging. Therefore, I think this manuscript can be accepted after the minor revision. The following are my comments:
1. In the introduction section, the authors mentioned the NBn detector which has great simplicity in structure and operation compared with the designed structure in this manuscript. I suggest the authors highlight the advantages of DBIRD over the NBn detector.
2. On page 3, line 102, the estimation of the optimal thickness of the RCA is not mentioned.
3. On page 3, Figure 1(a), the hole collection layer (HCL) is not shown in the band profile.
4. The formula (15) omitted the 1/f noise and G-R noise of the device which will lead to an overestimated D* value.
5. On page 3, line 280, the authors stated that “This value is high in comparison with that in the same dual-band detector using HgCdTe.”. I recommend the authors to cite this article, “128 x128 long-wavelength/mid-wavelength two-color HgCdTe infraredfocal plane array detector with ultralow spectracross talk, Optics Letters, 39,5184-5187(2014)” , which reported LW/MW two-color HgCdTe infrared FPA detector with ultralow crosstalks.
6. In the section 2.2, the authors mentioned the passivation process of the device. I recommend the authors to cite the article “A hybrid surfacepassivation on HgCdTe long wave infrareddetector with in-situ CdTe deposition and high-density Hydrogen plasma modification, Applied Physics Letters, 99,091101(2011)” which reported a hybrid surface passivation used to improve surface quality of typical n-on-p HgCdTe LWIR photodiode.
Author Response
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Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors have adequately addressed my comments in the revised manuscript.
Author Response
We express our deepest appreciation to the reviewer.
Reviewer 3 Report
Comments and Suggestions for AuthorsI didn’t the author give a strong response to my previous review comments. This manuscript can’t be accepted for publish.
As mentioned in my previous review, whether in single band or dual band detectors, barrier structure is not a new thing. There have been many theoretical and experimental results. In JOURNAL OF APPLIED PHYSICS 111, 073107 (2012), there is a detailed theoretical analysis about dual-band structure based with barrier. In APPLIED PHYSICS LETTERS 102, 011108 (2013), a M-barrier had been used in MWIR band. In Infrared Physics & Technology 86 (2017) 159–164, both MWIR and LWIR band use the M-barrier in order to reduce the dark current.
For the issue of simultaneous operation mentioned in the author’s response, I think the author should not fully understand the principle of simultaneous operation of dual-band detectors. All of the above detector structure can be fabricated for simultaneous operation. It's just a matter of subsequent ROIC and device fabrication (such as two or three indium bump).
Based on all of the above, my opinion for this manuscript is reject.
Author Response
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