Exciton-polaritons are bosonic eigenstates of semiconductor microcavities, consisting of a coherent mixing of quantum well excitons and cavity photons. Their density of states is four orders of magnitude smaller than that of excitons, which favors the possibility of reaching high occupancy factor before the breakdown of the exciton bosonic character. Thus polaritons are good candidates for the formation of a Bose condensate, particularly in II-VI microcavities due to the larger binding energy of II-VI excitons. Previous experimental studies of CdTe microcavities have clearly demonstrated that stimulated emission of polaritons can be obtained under non-resonant optical excitation. In this work, we present an experimental study of CdTe polaritons in this high excitation regime.
First, an angle resolved setup allows us to probe the polariton population along the dispersion curve. We observe that the emission dispersion becomes flat. We show that the latter effect can be well explained in terms of coherent collisions between in-phase polaritons. On a second hand, a microphotoluminescence setup allows us to observe a shrinkage and a shape modulation of the emission spot in real space in the stimulated regime. The spatial and transverse coherence of the emission will be discussed.

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1. Ultra-thin In-rich InGaN/GaN multiple quantum wells grown by metalorganic chemical vapor deposition