Theoretical evaluation of InTIP, InTIAs, and InTISb As longwave infrared detectors

Abstract

We have evaluated three III-V semiconductor alloys—In_1−xTl_xP (ITP), In_1−xTl_xAs (ITA), and In_1−xTl_xSb (ITS)—as possible candidates for future long-wave infrared (LWIR) detector materials. The cohesive energies, elastic constants, band structures, electron mobilities, and phase diagrams are calculated and are compared to those of Hg_1−xCd_xTe (MCT) alloys. The band gaps of all three III-V alloys change from negative to positive values as the alloy composition x decreases from 1 to 0. The x values for the 0.1-eV gap are estimated to be 0.67, 0.15, and 0.08, respectively, for ITP, ITA, and ITS. While both ITP and ITA form stable zincblende solid solutions for all alloy compositions, zincblende ITS is stable only for a range of x less than 0.15. The complication of the phase diagram in ITS is caused by the existence of a stable CsCl phase for pure TISb. The alloy mixing enthalpies for ITP and ITA are comparable to those in MCT, and their phase diagrams should be qualitatively similar, characterized by simple lensshape liquidus and solidus curves. Both ITP and ITA have considerably larger cohesive energies and elastic constants than those of MCT, indicating that they are structurally robust. At a 0.1-eV gap, the band structures near the gap and the electron mobilities in ITP, ITA, and ITS are also found to be comparable to those of MCT. Since the lattice constants of TIP and TIAs are less than 2% larger than the respective values in InP and InAs, the latter should provide natural substrates for the growth of active LWIR alloys and offer a potential to integrate the detector array and read-out circuit.