Picosecond Raman studies of the Fröhlich interaction in semiconductor alloys

Picosecond Raman studies on the prototypic alloys ${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As and ${\mathrm{In}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As show that substantial nonequilibrium phonon effects occur in spite of the break-down in wave-vector conservation engendered by alloy disorder. Phonon lifetimes, measured to be the same as in pure GaAs, also are unaffected by the disorder. Explicit expressions for the Fröhlich couplings of the two LO phonon modes in ${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As are obtained to compare with the generation rates of these phonons measured in our experiments.