Journal of luminescence vol:53 issue:1-6 pages:431-434
Picosecond time-resolved induced reflectivity measurements were performed in narrow well ( approximately 4.2 nm) GaAs/Al0.4Ga0.6As multiple quantum well systems in order to investigate fast excitonic relaxation. In a wide-barrier sample, - corresponding to independent subbands in each quantum well - a single exponential decay of the induced reflectivity is observed at very low power levels, corresponding to the population decay of the lowest exciton (hh1-e1). At higher excitation levels, a second, faster component appears, which is ascribed to exciton-exciton interactions. The amplitude of both components shows resonances at the energy of the lowest heavy and light hole exciton transitions. Comparison is made with induced transparency measurements on a back-etched specimen. In a thin barrier sample (L(B) almost-equal-to 4.2 nm) - in which the exciton states couple through the barriers - a short, energy dependent decay time is measured, for which correlation with the photoluminescence decay is not straightforward.