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

Abstract

The dependence on the scattering wave vector of a nonequilibrium LO phonon distribution generated by hot-electron relaxation is measured in thick GaAs and ${\mathrm{Al}}_{0.11}$${\mathrm{Ga}}_{0.89}$As layers, and a 500-\AA{} 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-\AA{} sample, demonstrates that Raman-active LO phonons in ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ have well-defined wave vectors and are not localized by alloy disorder.