Dependence of exciton formation on its center-of-mass momentum in quantum wells

We present a comprehensive study of the process of exciton formation due to exciton-phonon interaction. Using the exciton-phonon interaction arising from deformation potential, piezoelectric, and polar couplings, we have calculated the rate of formation of an exciton as a function of carrier densities, temperatures, and center-of-mass momentum (K-parallel to) in quantum wells. Our results show that excitons are dominantly formed at nonzero K-parallel to, which agrees very well with experiments. The formation of an exciton due to emission of longitudinal optical phonon is found to be more efficient at relatively small values of K-parallel to and that due to acoustic phonon emission is more efficient at relatively large K-parallel to values or carrier temperature Te-h less than or similar to 50 K.