Localization and wave-vector conservation for optical phonons in AlxGa1-xAs and thin layers of GaAs

The dependence on the scattering wave vector of a nonequilibrium LO phonon distribution generated by hot-electron relaxation is measured in thick GaAs and Al0.11Ga0.89As layers, and a 500- GaAs layer using picosecond Raman scattering in back and forward scattering geometries. The absence of q=0 nonequilibrium phonons in the thick samples, and their presence in the 500- sample, demonstrates that Raman-active LO phonons in AlxGa1-xAs have well-defined wave vectors and are not localized by alloy disorder. © 1988 The American Physical Society.