Microcavity polariton kinetics for bosonic condensation and lasing in II-VI compound materials

We investigate with a Boltzmann approach the relaxation kinetics of II-VI compound microcavity polaritons after a nonresonant pump pulse for the example of CdTe. In these polar materials large vacuum Rabi microcavity splittings guarantee robust polariton modes in the strong-coupling regime with an extremely small effective mass at the bottom of the lower branch, but with very short cavity lifetimes. Our kinetic treatment for stationary and picosecond-pulsed pumping takes the polariton-acoustic-phonon as well as the polariton-polariton scattering into account. For cavities with a vacuum Rabi splitting around Omega=10 meV, we find for nonresonant picosecond-pulse excitation a relaxation scenario which leads to a transient bosonic condensation in the lowest polariton state and coherent laser action at densities smaller than the exciton saturation density. For microcavities with a large vacuum Rabi splitting of Omega=26 meV we find due to the steep increase of radiative losses and the simultaneous steep decrease of the scattering rates with decreasing energy a nonequilibrium phase transition with a macroscopically occupied state in the bottleneck region at a finite transverse momentum and a connected coherent laser emission under an angle of 17 degrees. All of our results for medium and large Rabi vacuum splitting are in good qualitative agreement with corresponding observations of Dang and co-workers.