InAs/GaSb/AlSb Superlattice Detectors and Topological Superlattices
Dr. Philip Klipstein
Antimonide Based Compound
Semiconductor Research Program (ABCS),
Semiconductor Devices (SCD),
Location: QNC 1502
Abstract: As first predicted by Sai-Halasz, Tsu and Esaki in 1977, 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, HgxCd1-xTe (“MCT”), where the bandgap vanishes at a critical value of the composition parameter, x. MCT photodiodes are widely used as tunable infrared detector elements, because they offer a versatile technology that can match the characteristic photon wavelength of most infrared applications. On the other hand, InAs/GaSb photodiodes have suffered, historically, from higher dark currents and fabrication issues that have severely limited their uptake in similar applications. This position has changed recently, due to the development of a new XBp barrier architecture and a new and robust passivation process. A 640 x 512 format, 15 μm pitch LWIR focal plane array detector was demonstrated in 2016 by SCD, with a quantum efficiency of >50%, a pixel operability of >99%, and a dark current only about one order of magnitude larger than the state of the art Rule 07 value.
The SCD T2SL XBp detector contains both an InAs/GaSb active layer (AL) and an InAs/ AlSb barrier layer. The physical principles of the detector will be described, together with simulation methods that can predict the detector quantum efficiency and dark current from a basic definition of the superlattice period, the AL stack thickness and the minority carrier lifetime.
For layer thicknesses greater than the zero bandgap values, both InAs/GaSb/AlSb and HgTe/CdTe superlattices undergo a transition to a topological insulator phase (TI). Some basic 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 low temperature spintronic devices.
Bio: Between 1976 and 1982 Philip Klipstein received his B.A.and Ph.D. in Physics from Oxford and Cambridge Universities respectively. After two years as a Junior Research Fellow at Cambridge, he moved to a tenured post at Imperial College, London. Research included transport and optics in GaAs/AlAs and Si/Ge. In 1990, he returned to Oxford, adding research into antimonide heterostructures, and was promoted to Reader in 2000. Following a sabbatical at the Weizmann Institute, Israel, in 1998, he joined Semiconductor Devices (SCD) in 2001, where he is currently principal investigator of the Antimonide Based Compound Semiconductor research program (ABCS). He is author to more than 140 publications including 5 patents.