Effect of exciton-carrier thermodynamics on the GaAs quantum well photoluminescence

In order to explain the power-dependent temporal behavior of the photoluminescence from free excitons in a GaAs quantum well following a short optical pulse, we consider the excitons and free carriers to be a nearly ideal gas in thermodynamic equilibrium. The temperature of the gas, which decreases in time after the pulse due to cooling by phonon emission, can be measured experimentally from the free-carrier recombination luminescence. Because only excitons with near-zero kinetic energy can luminesce, the photoluminescence intensity depends on the excitonic-gas temperature. Due to the law of mass action between excitons and free carriers, the photoluminescence intensity of excitons also depends on the density of the gas, which decays in time. Using the known binding energy of excitons, we find that the density-dependent temporal behavior of the photoluminescence is consistent with a simple thermodynamic equilibrium between excitons and free carriers. © 1996 The American Physical Society.