Band engineered HOT midwave infrared detectors based on type-II InAs/GaSb strained layer superlattices Nutan Gautam a,⇑ , Stephen Myers a , Ajit V. Barve a , Brianna Klein a , E.P. Smith b , Dave Rhiger b , Elena Plis a , Maya N. Kutty a , Nathan Henry a , Ted Schuler-Sandy a , S. Krishna a a Center for High Technology Materials, Dept. of Electrical and Computer Engineering, University of New Mexico, Albuquerque, NM 87106, USA b Raytheon Vision Systems, Goleta, CA 93117, USA article info Article history: Available online 29 December 2012 Keywords: Infrared detectors Strained layer superlattice Midwave infrared Unipolar barriers Cascade abstract We report on heterostructure bandgap engineered midwave infrared photodetectors based on type-II InAs/GaSb strained layer superlattices with high operating temperatures. Bandgap and bandoffset tun- ability of antimonide based systems have been used to realize photodiodes and photoconductors. A uni- polar barrier photodiode, pBiBn, and an interband cascade photovoltaic detector have been demonstrated with a 100% cutoff wavelength of 5 lm at 77 K. The pBiBn detector demonstrated operation up to room temperature and the cascade detector up to 420 K. A dark current density of 1.6  10 7 A/cm 2 and 3.6  10 7 A/cm 2 was measured for the pBiBn and interband cascade detector, respectively, at 80 K. A responsivity of 1.3 A/W and 0.17 A/W was observed at 30 mV and 5 mV of applied bias for pBiBn and cascade detector, respectively, at 77 K. The experimental results have been explained by correlating them with the operation of the devices. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction There has been a demand for high operating temperature (HOT) midwave infrared (MWIR) detectors. Operation at high tempera- ture reduces cost of cryogenic cooling significantly leading to a reduction in size and total cost of the detector system. Type-II strained layer superlattice (T2SL) [1,2] based on the InAs/GaSb/ AlSb system has shown significant improvement in HOT detection in both MWIR and longwave infrared (LWIR) regimes. Recently, a MWIR focal plane array (FPA) based on T2SL has demonstrated operation up to 170 K [3], challenging the established InSb technol- ogy. Another technology which has shown tremendous develop- ment with HOT FPAs is InAsSb, which recently demonstrated imaging up to 180 K [4]. This places InAsSb technology as an emerging contender for T2SL based HOT MWIR photodiodes. How- ever, it must be lattice matched to GaSb with a composition of InAs 0.91 Sb 0.09 which makes it not suitable for fourth generation infrared detectors [5] as the cutoff wavelength cannot be changed. On the other hand, the InAs/GaSb T2SL system gives the flexibility of changing the cutoff wavelength by changing the composition and/or thickness of the layers. Furthermore, the strain in the sys- tem can be compensated enabling growth of thick detector structures. The T2SL structures based on the 6.1 Å family [6] (InAs, GaSb, AlSb) have the capability of bandgap and band-offset tunability. InAs/Ga(In)Sb T2SL, InAs/AlSb T2SL, GaSb/AlSb superlattice or any combination of these compounds, such as the W-structure [7] and the M-structure [8], can be tailored to achieve the required infrared bandgap. There is a type-II staggered alignment between the InAs and AlSb, while GaSb and AlSb demonstrate type-I nested alignment. The bandgap of InAs/Ga(In)Sb T2SL, for example, can be changed by just changing the thicknesses of constituent layers or by changing the composition of the ternary compound. The band-offset tunability is crucial for realization of barrier devices. There have been reports of advanced heterojunction architectures realized with the T2SL system, such as p-p-M-n [8], p-M-p [9], CBIRD [10], HSL [11], pBn [12], ALSL-B photodiode [13] and pBiBn [14], which have resulted in high performance devices. In this pa- per we report on a unipolar photodiode, based on the pBiBn archi- tecture, as well as an interband cascade detector for MWIR detection. The flexibility in tuning the bandgaps and bandoffsets of the antimonide system has been demonstrated in this work and it has been exploited to realize HOT detectors. 2. Heterojunction detector designs 2.1. MWIR pBiBn photodiode We report on a MWIR pBiBn photodiode based on the T2SL system. A LWIR pBiBn detector has demonstrated over two or- 1350-4495/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.infrared.2012.12.017 ⇑ Corresponding author. Address: 1313 Goddard St. SE, Albuquerque, NM 87106, USA. Tel.: +1 818 505 272 7849; fax: +1 818 505 272 7801. E-mail address: nutan.iitk@gmail.com (N. Gautam). Infrared Physics & Technology 59 (2013) 72–77 Contents lists available at SciVerse ScienceDirect Infrared Physics & Technology journal homepage: www.elsevier.com/locate/infrared