Ab initio study of phonons in wurtzite AlxGa1-xN alloys

We present a theoretical study of the zone-center optical phonons in wurtzi te AlxGa1-xN alloys over the whole compositional range from pure GaN to pur e AlN. The phonon modes are broadened upon alloying and their frequencies d isplay a blue shift with increasing Al concentration. The E-2 and E-1(TO) m odes display a two-mode like behavior and do not preserve a well-defined sy mmetry in the alloy but rather are mixed and have a large broadening. The L O modes, instead, display a one-mode behavior and have a well-defined symme try, small broadening, and a pronounced dependence of the frequency upon al loy composition. Therefore, we propose them as the best candidates for the compositional characterization of these materials. (C) 2000 American Instit ute of Physics. [S0003-6951(00)04815-4].