RADIATIVE LIFETIME OF FREE-EXCITONS IN QUANTUM-WELLS

We calculate the intrinsic radiative lifetime of excitons in quantum wells arising from the lack of translational invariance along the growth direction. For 100 angstrom wide GaAs-Ga(1-x)Al(x)As quantum wells, we compute a lifetime of 25 ps for the lowest heavy-hole exciton at zero in-plane wavevector. Since this is longer than typical thermalization times, the effective radiative decay rate is given by an average over the thermal distribution, resulting in an effective lifetime which increases linearly with temperature. A microscopic calculation of the reflectivity shows that the intrinsic radiative decay rate can also be measured in reflectivity experiments.