Mechanism of polariton-stimulation in a CdTe-based microcavity

At low temperature and for excitation densities well below the exciton satu ration density in CdTe microcavities, the photoluminescence (PL) intensity of the lower polariton mode strongly increases with a marked threshold beha viour. We present results of pump-probe experiments which show that the sti mulation of the lower polariton PL actually occurs in the strong exciton-ph oton 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 delta = E-C - E-X between exciton energy E-X and the cavity mode energy E-C. We show that: (i) our results cannot be int erpreted in terms of the localised exciton model; (ii) phonon relaxation an d exciton-exciton collisions or polariton-exciton collisions are involved i n the stimulation.