Lifetime of excitons in GaAs quantum wells

Time resolved luminescence measurements under resonant excitation were performed at 10 K on the free exciton in very high quality GaAs-AlAs quantum wells. At resonance, the luminescence intensity is increased by two orders of magnitude, and the decay is short. The radiative lifetime of the excitons in the radiant states is about 18 ps in agreement with the theory of Hanamura and Andreani. The lifetime of the thermalized excitons is about 80 ps at low excitation and it increases with the excitation density.