Exciton relaxation and radiative recombination in semiconductor quantum dots

Radiative lifetimes and acoustic-phonon scattering times of near-band-gap excitons are calculated. With increasing spatial quantization, exciton relaxation by phonon emission decreases strongly in efficiency as compared to radiative recombination. A rate-equation analysis based on the calculated lifetimes indicates an increasing shift of the luminescence from the exciton ground state towards excited states. For typical parameters of dots fabricated from quantum wells the calculated total luminescence efficiency is not strongly reduced by the effect of a slowed relaxation. The luminescence from the ground state becomes weak for strong spatial quantization.