THERMODYNAMICS OF EXCITONS IN COUPLED QUANTUM-WELLS

Because of their long lifetime in coupled quantum wells under an applied electric field, excitons may be able to reach thermodynamic quasi-equilibrium. Here we measure photoluminescence and photoluminescence excitation spectra from a symmetric coupled double quantum well. Analysis of the spectra shows that thermodynamic quasi-equilibrium is not achieved at temperatures below 6 K, where the excitons are trapped in a metastable distribution. At higher temperatures, quasi-equilibrium is achieved. Because of strong repulsion between the excitons, the quasi-equilibrium distribution can be modeled with a Fermi-Dirac distribution. The model quantitatively explains the striking temperature dependence of the photoluminescence linewidth which has been previously reported.