Excitons in Narrow Quantum Wells: Disorder Localization and Luminescence Kinetics

For narrow quantum wells, the energetic spread due to interface and alloy disorder is large enough to dominate the excitonic optical spectra. The resulting disorder potential enters the center-of-mass Schrödinger equation. We derive a kinetic equation for the exciton distribution over disorder eigenstates including acoustic phonon scattering and radiative recombination. The photoluminescence lineshape as function of temperature is studied. Both peak shift and width exhibit a nonmonotonous temperature dependence which is due to phonon-assisted thermal activation of localized excitons. A sharp low-energy drop in the photoluminescence excitation spectra can be understood in terms of a ‘relaxation mobility edge’.