Raman scattering spectra in mixedGa1−xAlxAs(Sb)crystals

A simplified Green's-function treatment is reported to explain the recent Raman scattering experiments in solid solutions with the zinc-blende structure. By incorporating phonons from an eleven-parameter rigid-ion model (RIM11) fitted-neutron (GaAs, GaSb), and optical (AlAs) data, we have studied the vibrations of low concentration of point defects in mixed ${\mathrm{Ga}}_{1-x}{\mathrm{Al}}_x\mathrm{As}\left(\mathrm{Sb}\right)\mathrm{}$ crystals. In the absence of precise experimental results, the present phenomenological method will be useful to predict the impurity-induced structure in different Raman-active irreducible representations by assuming derivatives of the polarizability tensor as free parameters. Explicit calculations are reported for $\mathrm{Ga} \mathrm{As}$:$\mathrm{Al}$, $\mathrm{Al} \mathrm{As}$:$\mathrm{Ga}$, and $\mathrm{Ga} \mathrm{Sb}$:$\mathrm{Al}$ systems. A reasonable explanation for the impurity modes and the Raman structure (wherever available) by a single perturbation parameter lend justification to the reliability of phonons by RIM11. This method may be significant for checking the internal coherence of those lattice-dynamical schemes which claim a good fit to the neutron data but suffer from internal inconsistencies. The force variation results for impurities obtained from a modified random-element-isodisplacement model fitted to the optical data (two-mode behavior) are compared and discussed with the full lattice-dynamical calculations.