Atomic ordering-induced band gap reductions in GaAsSb epilayers grown by molecular beam epitaxy

Abstract

A series of GaAs1−xSbx epilayers (0.51<x<0.71) grown by molecular-beam epitaxy on GaAs substrates with surface orientations of (001), (001) −8° toward (111)A, (001) −8° toward (111)B, (115)A, (115)B, (113)A, and (113)B were investigated using temperature-dependent Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy. Atomic ordering in these epilayers was observed from a decrease in the energy gap measured by FTIR absorption and corroborated by superlattice reflections in electron diffraction. Contrary to previous investigations of ordering in III-V alloys, a marked energy-gap reduction, corresponding to CuPt-B-type ordering, is observed in the GaAs1−xSbx grown on (111)A-type substrate offcuts.