EFFECT OF EXCITON-CARRIER THERMODYNAMICS ON THE GAAS QUANTUM-WELL PHOTOLUMINESCENCE

In order to explain the power-dependent temporal behavior of the photo luminescence from free excitons in a GaAs quantum well following a she a optical pulse, we consider the excitons and free carriers to be a ne arly ideal gas in thermodynamic equilibrium. The temperature of the ga s, which decreases in time after the pulse due to cooling by phonon em ission, can be measured experimentally from the free-carrier recombina tion luminescence. Because only excitons with near-zero kinetic energy can luminesce, the photoluminescence intensity depends on the exciton ic-gas temperature. Due to the law of mass action between excitons and free carriers, the photoluminescence intensity of excitons also depen ds on the density of the gas, which decays in time. Using the known bi nding energy of excitons, we find that the density-dependent temporal behavior of the photoluminescence is consistent with a simple thermody namic equilibrium between excitons and free carriers.