Ab initio study of phonons in wurtzite AlxGa1−xN alloys

Abstract

We present a theoretical study of the zone-center optical phonons in wurtzite ${\mathrm{Al}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N}$ alloys over the whole compositional range from pure GaN to pure AlN. The phonon modes are broadened upon alloying and their frequencies display a blue shift with increasing Al concentration. The $E_2$ and $E_1\mathrm{(TO)}$ modes display a two-mode like behavior and do not preserve a well-defined symmetry in the alloy but rather are mixed and have a large broadening. The LO modes, instead, display a one-mode behavior and have a well-defined symmetry, small broadening, and a pronounced dependence of the frequency upon alloy composition. Therefore, we propose them as the best candidates for the compositional characterization of these materials.