Type-II superlattice hole effective masses

Abstract

A long wavelength infrared (LWIR) type-II superlattice (T2SL) is typically characterized by a very large valence-band-edge curvature effective mass, which is often assumed to lead to poor hole mobility. A detailed examination of the LWIR T2SL heavy-hole 1 (hh1) band structure reveals that a hole with non-zero in-plane momentum (k‖≠0) can move with a much larger group velocity component along the growth direction than one at the band edge (k‖=0), and that the hh1 miniband width can exhibit a very strong dependence on the in-plane wavevector k‖. To distill the band structure effects relevant to hole transport into a simple quantity, we describe a formulation for computing the thermally averaged conductivity effective mass. We show that the LWIR T2SL hole conductivity effective masses along the growth direction can be orders of magnitude smaller than the corresponding band-edge curvature effective masses. We compare the conductivities effective masses of InAs/GaSb T2SL and InAs/InAsSb T2SL grown pseudomorphically on GaSb substrate, as well as the metamorphic bulk InAsSb and InAs/InAsSb T2SL.