Determination of the fundamental and spin-orbit-splitting band gap energies of InAsSb-based ternary and pentenary alloys using mid-infrared photoreflectance

In narrow-gap semiconductors, non-radiative Auger recombination losses (via conduction, heavy-hole, spin split-off hole, heavy-hole processes) are sensitive to how the band gap energy, E0, compares to the spin-orbit splitting, Δ0. However, narrow-gap band structures have often not been very well characterised. We report on the mid-infrared photo-modulated reflectance of E0 and E0 + Δ0 transitions in high-quality, InAs-rich InAsSb and GaInAsPSb samples as functions of both temperature (T = 10-300 K) and antimony content ≤ 22.5%, for wavelengths up to ~ 4.75 μm. The measured T-dependence of E0 is generally consistent with that accepted in the literature and we confirm that Δ0 is T-independent. As a function of Sb fraction, E0 is consistent with the positive bowing parameter of + 670 meV quoted in the literature. However, Δ0 does not exhibit the currently accepted positive bowing parameter of + 1170 meV: rather, a best fit to our data tentatively suggests a negative bowing of ~ − 165 meV. Due to the importance of Δ0 in predicting and interpreting the performance of InAsSb-based devices, this result is expected to have a significant impact.