Photoluminescence and optical gain due to exciton-electron scattering in a high quality GaN thin film

We have investigated photoluminescence (PL) properties of a high quality GaN thin film grown by metal organic vapor phase epitaxy under intense excitation conditions in a high temperature regime from 120 K to room temperature. It is found that a PL band peculiar to intense excitation conditions appears with a threshold-like behavior. The energy spacing between the PL band at the threshold excitation power and the A exciton is proportional to temperature. The extrapolation of the linear dependence results in zero value of the energy spacing at absolute zero temperature. These PL profiles are specific to an emission process originating from exciton-electron scattering. Furthermore, we have demonstrated that the exciton-electron scattering process produces optical gain at room temperature from measurements of PL with a variable stripe-length method. (c) 2006 American Institute of Physics.