Compositional dependence of the Raman frequencies and line shapes of ${\mathrm{Cd}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{Zn}}_{\mathrm{x}}$Te determined with films grown by molecular-beam epitaxy

Raman scattering measurements are used to investigate the lattice-dynamic properties of ${\mathrm{Cd}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Zn}}_{\mathrm{x}}$Te. The samples were thin films grown by molecular-beam epitaxy on GaAs substrates. The first-order Raman spectra for the ternary samples show two sets of longitudinal- and transverse-optical (LO,TO) modes, which arise from CdTe- and ZnTe-like vibrations. The compositional dependence of the lattice frequencies is that of a typical two-mode system. The mode oscillator strengths were evaluated from the measured frequencies. The line shapes of the LO Raman bands display asymmetrical broadenings which are observed to increase with decreasing LO-TO splitting. The LO bands were fitted with the predicted line shapes of the discrete-continuum interaction and the spatial-correlation models. The Fano line-shape of the discrete-continuum interaction model allows good fittings of both sets of LO Raman bands. The spatial-correlation model does not reproduce the line shapes of the ZnTe-like LO modes for x≃0.5.