PHOTOLUMINESCENCE OF MOLECULAR-BEAM EPITAXIAL GROWN AL0.48IN0.52AS

This article provides an in-depth study of the photoluminescence (PL) and photoluminescence excitation (PLE) from Al0.48In0.52As grown by molecular beam epitaxy that exhibits linewidths of approximately 17 meV, comparable with the best reported to date. When the sample temperature is increased from 2 K the emission energy exhibits an inverted S-shape dependence and this is normally associated with exciton localization. It is suggested that this anomalous temperature dependence occurs because the emission is a convolution of more than one transition from 35 K to 65 K. The 2 K emission intensity quenches with an activation energy of 17.5+/-2.5 meV. A similar difference in energy of 17-20 meV is also observed between the PL and PLE spectrum and this has been explained by alloy fluctuations and a localization of the exciton. It is suggested that due to the close proximity of the GAMMA-X crossover that non-GAMMA contributions to the donor binding energy cannot be dismissed. The large luminescence linewidth observed in Al0.48In0.52As compared to other ternary alloys cannot be attributed to alloy scattering alone. If non-GAMMA contributions to the donor binding energy are present excitons will be more localized sensing any local fluctuations in the alloy composition. However, we have demonstrated the difficulties in proving any direct correspondence between the luminescence linewidth and clustered regions. The emission from Al0.48In0.52As may not be excitonic as it could also be attributed to a neutral donor to free hole transition (D-degrees, h). Band-edge emission is not observed in the luminescence spectrum until the sample temperature reaches approximately 100 K.