Long Wavelength InAs/InAsSb Infrared Superlattice Challenges: A Theoretical Investigation
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https://doi.org/10.1007/s11664-020-08349-7 Ó 2020 The Minerals, Metals & Materials Society
TOPICAL COLLECTION: U.S. WORKSHOP ON PHYSICS AND CHEMISTRY OF II-VI MATERIALS 2019
Long Wavelength InAs/InAsSb Infrared Superlattice Challenges: A Theoretical Investigation DAVID Z. TING ,1,2 AREZOU KHOSHAKHLAGH,1 ALEXANDER SOIBEL,1 and SARATH D. GUNAPALA1 1.—Jet Propulsion Laboratory, California Institute of Technology, 231, 4800 Oak Grove Drive, Pasadena, CA 91109-8099, USA. [email protected]
M/S 3022.—e-mail:
InAs/InAsSb type-II superlattice focal plane arrays that demonstrate high operability and uniformity with cutoffs ranging from 5 lm to 13 lm have already been demonstrated. Compared to InAs/GaSb, the InAs/InAsSb superlattice is easier to grow and has longer minority carrier lifetimes, but requires a longer superlattice period to achieve long or very long wavelength cutoffs. A longer type-II superlattice period leads to smaller absorption coefficients and larger growth-direction hole conductivity effective masses. We explore by theoretical modeling some of the ideas aimed at addressing these challenges for the long and very long wavelength InAs/InAsSb superlattice. Increasing the Sb fraction in the InAsSb alloy can reduce the InAs/InAsSb superlattice period significantly, but this benefit can be negated by Sb segregation. Thin AlAsSb barrier layers can be inserted in InAs/InAsSb to form polytype W, M, and N superlattices in order to increase electron–hole wavefunction overlap for stronger optical absorption. However, this strategy can be unfavorable since the AlAsSb barriers increase the band gap, and thereby increase the superlattice period required to reach a given cutoff wavelength. Metamorphic growth on virtual substrates with larger lattice constants than GaSb can decrease the superlattice period needed to reach a specified cutoff wavelength, but this benefit should be weighed against the need for metamorphic buffer growth and the resulting higher defect density. Key words: Infrared detector, unipolar barrier, type-II superlattice, InAs/InAsSb superlattice
INTRODUCTION The InAs/InAsSb (gallium-free) type-II strainedlayer superlattice (T2SLS) has emerged as an alternative to the more established InAs/GaSb type-II superlattice (T2SL) for infrared detector applications. We have previously documented the
(Received January 29, 2020; accepted July 21, 2020)
history of the InAs/InAsSb T2SLS,1 as well as the development of InAs/InAsSb T2SLS infrared detectors at the NASA Jet Propulsion Laboratory (JPL).2 InAs/InAsSb T2SLS focal plane arrays (FPAs) with high operability and uniformity have been demonstrated in mid-wavelength infrared (MWIR), long wavelength infrared (LWIR), and very long wavelength infrared (VLWIR)1; focal plane arrays with cutoffs ranging from 5 lm to 13 lm were briefly discussed in Ref. 1. In particular, FPAs based on the mid-wavelength (MW) InAs/InAsSb T2SLS unipolar barrier infrared detector3,4 have demonstrated significantly higher operating temperature than their InSb counterparts whil
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