Electrically Injected Exciton-Polariton Lasers
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Conventional semiconductor lasers operate on the principle of stimulated emission of radiation. In contrast, exciton-polaritons or polaritons, which are part-light, part-matter Bosonic quasiparticles, offer an entirely different physical principle for realizing a coherent light emitter. These relatively new solid-state devices are commonly known as polariton lasers, which emit coherent light by spontaneous emission without the need for population inversion or stimulated emission. Polariton lasers operate in the exciton-cavity photon strong coupling regime. Practical applications of these ultra-low threshold coherent light sources necessitate the need to develop electrically pumped devices which can operate at high temperatures. The operation of GaAs-based electrically pumped polariton lasers, which are usually designed using the surface emitting geometry, has remained limited to cryogenic temperatures. Though a room temperature electrically pumped polariton laser has been recently demonstrated in our group, using a GaN-based microcavity, several important performance characteristics of these light sources have hitherto remained unexplored.
In the present study, GaAs- and GaN-based polariton laser diodes have been experimentally realized which can operate at 155K and 300K, respectively. A novel edge-emitting device configuration, in contrast to the more commonly used surface surface-emitting one, has been employed. The polariton lasing threshold of these devices are ~20-250 times smaller than comparable conventional semiconductor photon lasers. Steady-state output polarization and small-signal modulation response of the polariton lasers have been measured and analyzed for the first time. The role of defects on the performance characteristics of polariton lasers has also been investigated and elucidated. Finally, the possibility of realizing a low power optical amplifier based on strong coupling has been studied experimentally.