Single-mode behavior ofAlSb1−xAsxalloys

Raman scattering is used to characterize the long-wavelength optical-mode behavior of ${\mathrm{AlSb}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{As}}_{\mathit{x}}$ alloys grown by molecular-beam epitaxy, for a variety of As mole fractions. Single LO and TO modes are observed for 0≤x≤1, at frequencies depending on the As concentration. This behavior is characteristic of single-mode alloys. The single-mode behavior of ${\mathrm{AlSb}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{As}}_{\mathit{x}}$ disagrees with theoretical predictions, and calls for a review of the theory of optical modes in ${\mathit{AB}}_{1\mathrm{-}\mathit{x}}$ ${\mathit{C}}_{\mathit{x}}$ crystals.