InAs/GaSb Type II superlattices (T2SLs) are a promising III-V alternative to HgCdTe (MCT) for infrared Focal Plane Array (FPA) detectors. Over the past few years SCD has developed the modeling, growth, processing and characterization of high performance InAs/GaSb T2SL detector structures suitable for FPA fabrication. Our LWIR structures are based on an XBpp design, analogous to the XBnn design that lead to the recent launch of SCD’s InAsSb HOT MWIR detector (TOP= 150 K). The T2SL XBpp structures have a cut-off wavelength between 9.0 and 10.0 μm and are diffusion limited with a dark current at 78K that is within one order of magnitude of the MCT Rule 07 value. We demonstrate 30 μm pitch 5 x 5 test arrays with 100% operability and with a dark current activation energy that closely matches the bandgap energy measured by photoluminescence at 10 K. From the dependence of the dark current and photocurrent on mesa size we are able to determine the lateral diffusion length and quantum efficiency (QE). The QE agrees very well with the value predicted by our recently developed k ∙ p model [Livneh et al, Phys. Rev. B86, 235311 (2012)]. The model includes a number of innovations that provide a faithful match between measured and predicted InAs/GaSb T2SL bandgaps from MWIR to LWIR, and which also allow us to treat other potential candidate systems such as the gallium free InAs/InAsSb T2SL. We will present a critical comparison of InAs/InAsSb vs. InAs/GaSb T2SLs for LWIR FPA applications.
Keywords: Infrared Detector, Focal Plane Array, Type II superlattice, Gallium free superlattice, Bariode, XBn, XBp, pBp, LWIR.
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