Far-infrared reflectance and first- and second-order Raman spectra were carefully measured at room temperature on a series of AlxGa12xSb layers epitaxially grown on GaSb ~with 0.0<x<0.5). For all the compositions the clean ‘‘two-mode’’ behavior of lattice vibrations was confirmed. The fit of the reflectance curves with classical dielectric functions yielded the compositional variation of the TO and LO phonon frequencies, which are in very good agreement with the Raman results, as well as the oscillator strengths and the line broadenings. The effects of cation disorder were evidenced in both the reflectance and Raman spectra. A comparison was made with previous data, which show some scattering and discrepancies, having been measured by a single technique ~reflectance or Raman! on samples with different characteristics.
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