Electron-density-dependent variation of the relative strength of the dual polar optical modes in Al_xGa_1-xAs as detected by Raman scattering

The Raman signal in Al_xGa_1-xAs has been determined via an ensemble Monte Carlo simulation. We find that the relative scattering of the AlAs-type phonons has an electron density dependence, which has been confirmed experimentally. These results explain the experimental differences seen in the literature. Raman scattering samples the lower momentum flank of the phonon distribution; these phonons arise from contributions by high-energy electrons. As the electron density increases, more electrons occupy these higher-energy states. Only when these higher-energy states are sufficiently occupied does the Raman scattering become a true measure of the "average" scattering in the system.