Polariton relaxation in semiconductor microcavities: Efficiency of electron-polariton scattering

We report on the experimental study of polariton relaxation in the presence of a photo-injected electron gas. The population along the polariton branches is measured for various excitation conditions through angle resolved photoluminescence. The electron gas is shown to induce a redistribution of the population along the lower polariton branch with a strong population increase close to the center of the Brillouin zone. However, even in the presence of electrons, polariton-polariton scattering is shown to remain the most efficient relaxation process. We analyze why electron-polariton scattering is not as efficient in the present microcavity structure as theoretically predicted.