High absorption long wave infrared superlattices using metamorphic buffers

Abstract

The narrow band gap and staggered band alignment of InAsSb alloys make it possible to engineer type-II superlattices (T2SLs) for mid-wave and long-wave (LW) infrared sensors operating in the 3–12 μm range. However, InAs/InAsSb T2SLs that are strain balanced to the underlying GaSb substrate have much lower absorption coefficients for LWIR operation because of the larger superlattice (SL) period, leading to reduced electron-hole overlap. The absorption coefficient of T2SLs can be greatly improved by growing on metamorphic buffers (MBs) with reduced lattice mismatch to the InAsSb layers, which allows the SL period to be reduced. For this study, MBs were capped with InAs/InAsSb T2SLs to assess the suitability of the materials for detector applications by X-ray diffraction and photoluminescence lifetime measurements. We show that the absorption of T2SLs can be significantly increased with no apparent degradation in the minority-carrier lifetime.