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Dissertation Defense

Strong Coupling and Magnetic Field Effects in Microcavity Light Sources

Ayan Das

Room temperature Bose-Einstein condensation and electrically injected ultra-low threshold exciton-polariton lasing was achieved in a strong coupled microcavity. Exciton-polaritons are half-light, half-matter bosonic quasi-particles that are formed in a microcavity under the strong coupling regime. For optically injected devices and room temperature demonstration of lasing and dynamic condensation, a single GaN or ZnO nanowire (length ~ 1 µm and diameter ~ 100 nm) was used as the active material. These nanowires are unique in the sense that they are free of extended defects and have negligible strain and polarization field. Bose-Einstein condensation was achieved at room temperature by employing evaporative cooling technique in a compositionally graded Al(Ga)N nanowire with a spatial potential trap. For practical application in light sources currently limited by a high energy consumption, polariton lasers with electrical injection should be extremely useful. Exciton-polariton laser diodes were demonstrated in this dissertation, for the first time, by a combination of modulation doping to overcome the 'relaxation bottleneck' and by applying a magnetic field to increase the exciton saturation density.

Sponsored by

Professor Pallab K. Bhattacharya