Atomic Ordering-Induced Band Gap Reductions In Gaassb Epilayers Grown By Molecular Beam Epitaxy

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 degrees toward (111)A, (001) -8 degrees 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. (C) 2005 American Institute of Physics.