Mechanism of polariton-stimulation in a CdTe-based microcavity

At low temperature and for excitation densities well below the exciton saturation density in CdTe microcavities, the photoluminescence (PL) intensity of the lower polariton mode strongly increases with a marked threshold behaviour. We present results of pump-probe experiments which show that the stimulation of the lower polariton PL actually occurs in the strong exciton-photon coupling regime. We present also a detailed study of this stimulation effect as a function of the number of quantum wells in the microcavity and as a function of the detuning δ = E_C-E_X between exciton energy E_X and the cavity mode energy E_C. We show that: (i) our results cannot be interpreted in terms of the localized exciton model; (ii) phonon relaxation and exciton-exciton collisions or polariton-exciton collisions are involved in the stimulation.