Electronic Transport in Ultra-Narrow-Bandgap InAs/InGaSb Superlattices on Conductive GaSb Substrates

Abstract The electronic properties of an ultra-narrow-bandgap InAs/InGaSb type II superlattice (T2SL) were investigated for potential terahertz applications using magnetic field-dependent transport measurements and mobility spectrum analysis over a temperature range of 10–300 K. Since the 267.2-nm-thick 40-period T2SL structure was grown on electrically conductive undoped p -type GaSb substrates, detailed transport characterization of all carrier species in representative substrate-only and substrate/buffer reference samples was essential to unambiguously discriminate carriers. The results indicate that a single high-mobility electron species dominates electronic transport in the T2SL structure over the range of 56–300 K. From analysis of the sheet electron density, a temperature-dependent energy bandgap Varshni model was extracted, revealing that the T2SL bandgap can be tuned from 13 meV at 80 K, down to 1.3 meV at 115 K, corresponding to cutoff frequencies in the range of 0.3 to −3.2 THz range. In addition, the results indicate an InAs/GaSb valence band offset (VBO) of 0.605 eV, which is consistent with a T2SL characterized by InSb-like interface bonds.