Free Exciton Radiative Recombination in GaAs Quantum Wells

Radiative properties of free excitons in GaAs quantum wells are studied under resonant excitation. We first show that we do observe free excitons by their Lorentzian lineshape and their mobility in the plane of the well. Enhanced radiative recombination of the excitons, a consequence of the breakdown of the translational symmetry induced by the quantum well potential, is evidenced by the very short lifetime as well as by the strong intensity of the luminescence signal. Dephasing mechanisms, by transferring the excitons into non-radiative states, increase the observed lifetime. In the same way, the increase of the sample temperature, or of the exciton temperature by non-resonant excitation, increases the radiative decay time by reducing the exciton population close to k = 0. From our experiments, we deduce a radiative lifetime of 10 ± 4 ps in the absence of dephasing mechanisms.