Room temperature strong coupling effects and polariton lasing under electrical injection

When an emitter is placed in a resonant cavity, then in the strong coupling regime of light-matter interaction the degeneracy between the emitter and cavity photon is lifted, giving rise to two light-matter entangled eigenstates separated by a characteristic interaction energy (Rabi splitting) Ω_VRS. These are the lower and upper exciton-polariton branches, which are the normal modes of the system. Upon suitable excitation, a coherent state of exciton-polaritons is generated by polariton-phonon scattering and eventual stimulated polariton-polariton scattering, which is a phase coherent process and is the relevant gain mechanism. The coherent polariton state generates coherent light by spontaneous radiative recombination. This inversionless process of coherent emission has been termed polariton lasing. An electrically pumped GaAs-based polariton laser was demonstrated for the first time recently by Bhattacharya et al. [1] and Schneider et al. [2]. Because of the small exciton binding energy of excitons in the In_0.1Ga_0.9As quantum wells in the devices, operation had to be restricted to cryogenic temperatures (10-30 K). We report here, for the first time, high temperature electrically pumped polariton lasers using different material systems. In the first, where the emitter is a single Al_0.31Ga_0.69As/Al_0.41Ga_0.59As quantum well, operation is demonstrated at 155 K. Room temperature operation is demonstrated with a GaN-based microcavity device.