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In this work, we report a polarized Raman study on the vibrational properties of the InAs/InAs1-xSbx SLs as well as selected InAs1-xSbx alloys, all grown on GaSb substrates by either MBE or MOCVD, from both growth surface and cleaved edge.

InAs${}_{1-x}$Sb${}_{x}$ type-II superlattices (T2SLs) are of significant interest for next-generation infrared photodetectors, due to their long minority-carrier lifetime. However, little is known about hole transport along the growth axis, the direction of photocurrent flow. This study presents quantitative measurements of vertical hole transport in band-engineered T2SL transistors, which turns out to be strikingly similar to electronic transport in disordered bulk semiconductors like amorphous silicon. These results carry significant implications for optimizing T2SLs and devices based on them.

Semiconductor type-II superlattices (T2SLs) are of prime interest for medium- and long-wavelength infrared photodetectors, and possibly as thermophotovoltaics. Their properties can be spoiled, though, by defect states with energies in the band gap, which promote carrier recombination. This optical study of a series of T2SLs reveals that the SRH defect state presents just one energy, nearly independent of the band gap or edges. Thus it seems possible to engineer T2SLs with no defect levels in the gap, for improved performance.

A judicious choice of material heterostructure could spur a breakthrough in infrared photodetector technology, for diverse uses in astronomy, medicine, and industry. Unfortunately, for this system little is known about the nonequilibrium charge-carrier dynamics, which is critical to device performance. This study outlines an approach to uniquely determine the magnitudes of the various recombination mechanisms that determine carrier lifetime, and ultimately the limitations of photodetector dark currents.