Disorder-activated acoustic mode in raman spectrum of GaxAl1-xAs

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 GaxAl1-xAs, a simple theory has been successfully applied to obtain information on the electronic states. © 1972 The American Physical Society.