A combined single-phonon Raman and photoluminescence study of direct and indirect band-gap Al x Ga1− x As alloys grown by molecular-beam epitaxy

A combined Raman and photoluminescence study of one-phonon processes in direct and indirect band-gap AlxGa1−xAs alloys grown by molecular-beam epitaxy is presented. The appearance of the ‘‘forbidden’’ TO mode is attributed to twinning effects related to growth rather than the possible experimental deviation from the strict backscattering geometry or the presence of alloy disorder. LO phonons around X as well as Γ and L points are found to contribute to the phonon-assisted exciton recombination process though the dominant contribution is from phonons around the X point. A discrepancy between the results of existing methods of determining alloy concentration from Raman and photoluminescence data is found, indicating the need for reevaluation and further refinement of such methods.