Band alignment in a short-period InAsSb superlattice via cross-sectional STM

Narrow bandgap semiconductor heterostructures provide a platform for realizing topologically non-trivial electronic structure, useful for quantum information devices. However, the band alignment, a crucial element of band engineering, is not well described for short-period InAsSb superlattices within the small bandgap range of alloy concentrations. We utilize cross-sectional scanning tunneling microscopy (STM) at 77K to obtain topographical and electronic information over the (110) cross section of a short-period InAs0.665Sb0.335/InAs0.235Sb0.765 superlattice with thickness 4.3 and 2.4 nm, respectively. The band alignment data was obtained in areas of the superlattice both near to and far from the Al0.645In0.355Sb virtual substrate. Over the superlattice, an anomalous negative differential tunneling conductance was observed consistently. We propose that the origin of this effect is related to the unusual electronic structure of the superlattice, which is predicted to have nearly inverted electron and hole states. Additionally, we observe apparent strain relaxation and a local c(2 × 2) surface reconstruction which will be discussed.