Disorder-Activated Acoustic Mode in Raman Spectrum ofGaxAl1−xAs

Abstract

We report the observation of an acoustic phonon mode, usually not Raman active, which is interpreted here as a disorder-activated longitudinal acoustic mode. Because of good matching of lattice constants and nearest-neighbor force constants in the alloy system ${\mathrm{Ga}}_x{\mathrm{Al}}_{1-x}\mathrm{As}$, a simple theory has been successfully applied to obtain information on the electronic states.