Résumé:

In the field of polariton physics, ZnO has attracted a large attention due to it large exciton binding energy and oscillator strength, that enable to observe strong coupling at room temperature. We have recently demonstrated polariton condensation in such a cavity presenting a large quality factor (>2000) [1]. In the present work, we study the time-resolved spectroscopy of the polariton emission in this cavity, in order to assess the critical parameters of the polariton dynamics and their temperature dependance. We also study the theoretical model for the dynamics of microcavity polaritons. Figure 1 presents the experimental study of the photoluminescence dynamics of cavity polaritons. The measured exciton lifetime is about 50ps at 80K and at exciton densities close to the condensation threshold. It is rather independent of the temperature. It also governs the decay of each polariton branch fed by the exciton reservoir. Our modeling clarifies the time-constants involved in the exciton and polariton dynamics. In particular, we address the problem of the relative efficiencies of exciton formation assisted by either optical longitudinal phonons (LO) or acoustic phonons, and the following relaxation towards the polariton branches. We resolve the classical Boltzmann equation [2] which describes the relaxation kinetics of bosonic polariton. The energy relaxation rates of heated excitons due to emission and absorption of phonons have been calculated as a function of the lattice temperature. References [1] F. Li et al., Phys. Rev. Lett. 110, 196406 (2013) [2] G.Malpuech et al., Phys. Rev. B. 65,153310 (2002)