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Published online by Cambridge University Press: 01 February 2011
Spontaneous atomic ordering is investigated in a series of GaAs1−xSbx epilayers (0.51 < x < 0.71) grown by molecular beam epitaxy (MBE) 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. Atomic ordering in these epilayers was observed from a decrease in the energy gap measured by Fourier transform infrared (FTIR) absorption spectroscopy and corroborated by superlattice reflections in transmission electron diffraction and Raman spectroscopy. 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 orientations.