EXCITON RELAXATION DYNAMICS IN ULTRATHIN CDSE/ZNSE SINGLE QUANTUM-WELLS

Ultrathin CdSe/ZnSe single quantum wells grown by self-limiting monolayer epitaxy are investigated by means of time integrated as well as picosecond time-resolved luminescence spectroscopy. Well thicknesses are 1, 2 and 3 monolayers of CdSe. All samples exhibit a bright excitonic luminescence which shows, for an SQW of one monolayer thickness, a blue shift of 850 meV with respect to bulk CdSe. The transient behavior of the luminescence varies depending on energy of detection. At high energies, the decay is very fast and nonexponential. At the low-energy side of the luminescence band, a slower, simply exponential decay is observed. A model of excitons relaxing in a random potential is set up to describe and discuss the experimental data. Under resonant excitation into higher well states, several phonon replica of recombining, resonantly excited excitons occur.