Dissertation Defense

Properties of III-Nitride-Based Polariton and Spin Polariton Diode Lasers

Aniruddha Bhattacharya


The strong coupling regime of emitter-photon interactions gives rise to new
quasiparticles known as exciton-polaritons, which have been efficiently utilized to demonstrate
inversionless coherent emission, or polariton lasing in submicron-scale optical cavities. The main
focus of the dissertation research was the study of the output polarization characteristics of GaN-based polariton lasers operated with unpolarized and spin-polarized electrical injection.
Electrical spin injection in a bulk GaN-based microcavity polariton diode laser also enables the
realization of an electrically modulated circularly-polarized low-energy coherent light source.
Successful electrical spin injection in bulk GaN, which is the contact as well as the active layer
of the spin polariton diode laser, has been independently confirmed from room-temperature four-terminal Hanl spin precession measurements made on GaN-based spin valves, and observation of hysteretic circular polarization in edge-emitting light-emitting diodes. Complementary theoretical calculations related to these spin polariton lasers have also been performed. Excitation-dependent photocurrent of the microcavity diodes exhibits a non-linear enhancement with a threshold, which is consistent with the polariton lasing threshold. This is a unique manifestation of the bosonic stimulation effect in polariton lasers. Preliminary work showing super-linear emission characteristics in the excitation regime between polariton and photon lasing regimes will also be discussed.

Sponsored by

Professor Pallab Bhattacharya