Exciton dynamics in a CdSe/ZnSe multiple quantum well

We use time-resolved spectroscopy to study exciton relaxation at 10 K in a CdSe/ZnSe multiple quantum well that exhibits well-thickness fluctuation. Three distinct relaxation processes contribute to the time evolution of the luminescence. The first is the localization of excitons into local band-gap minima with a time constant similar to 4 ps, which includes hot-exciton formation and cooling. The second process is the migration of localized excitons between local minima, which is a tunneling process accompanied by phonon emission; it cannot be described by a single time constant and strongly depends on energy. The final contribution to the process is the recombination of localized excitons with a time constant similar to 470 ps.