Raman scattering and optical-absorption studies of the metastable alloy system ${\mathrm{GaAs}}_{\mathrm{x}}$${\mathrm{Sb}}_{1\mathrm{-}\mathrm{x}}$

The optical properties of ${\mathrm{GaAs}}_{\mathrm{x}}$ ${\mathrm{Sb}}_{1\mathrm{-}\mathrm{x}}$ alloys grown across the entire concentration range by multitarget sputter deposition are reported. X-ray diffraction, optical absorption, and Raman spectra show the samples to be single-crystal, single-phase alloys for all x, including those in the miscibility gap. Alloy lattice constants are found to vary linearly with concentration. The direct Γ-point energy gaps, determined from optical-absorption measurements, show significant negative bowing. Contrary to previous reports, the Raman spectra exhibit two-mode behavior throughout, including a local mode of As in GaSb and a resonant mode of Sb in GaAs. An analysis of peak frequencies and line shapes versus concentration is given in the context of disorder effects. We observe broadenings much less severe and asymmetric than those seen in similar systems and usually interpreted in terms of k≠0 density-of-states activation. The observed adherence to zone-center selection rules for all x, suggests a more accurate interpretation to be one involving the k≊0 spectral projection of the density of states.