Models Of InAs/(GaSb,InAsSb) And HgTe/CdTe Superlattice Detectors and Beyond

Type II superlattices (T2SLs) based on alternating layers of InAs and GaSb exhibit rather unique properties, including a zero bandgap at a critical value of the layer thicknesses. In this respect, T2SLs bear a close relationship to the alloy, Hg_xCd_1-xTe (“MCT”), where the bandgap vanishes at a critical value of the composition parameter, x. Recently, a 15 μm pitch T2SL LWIR array detector was demonstrated by SCD, based on a new XBp barrier architecture and a new and robust passivation process[1]. This detector is made entirely from III-V materials but exhibits performance comparable to high quality MCT detectors.

The SCD T2SL XBp detector contains both an InAs/GaSb active layer (AL) and an InAs/AlSb barrier layer. A k · p simulation method will be described which can predict both the QE and dark current with reasonable precision, from a basic definition of the superlattice period and the AL stack thickness. Results are compared with other types of superlattice including InAs/InAsSb and HgTe/CdTe. The method introduces a number of novel features including the use of an interface matrix, and a way of calculating the Luttinger parameters from standard reference values.

For layer thicknesses greater than the critical values, both InAs/GaSb and HgTe/CdTe superlattices undergo a transition to a topological insulator phase (TI). Some of the properties of the topological phase will be discussed, including a graphene like dispersion at the TI transition and possible advantages of the TI phase for spintronic and THz devices[2].

[1]. P.C. Klipstein et al., "Type-II superlattice detector for long-wave infrared imaging”, SPIE 9451, 94510K (2015)

[2]. P.C. Klipstein, “Structure of the QSH states in HgTe/CdTe and InAs/GaSb/AlSb QWs” Phys. Rev. B 91, 035310 (2015)