Exciton-polaritons are an exciting composite quasiparticle. Part exciton and part photon, they bring to-gether many of the advantages of both underlying parts. The excitons lend their strong interactions, and the photons give an extremely light mass, creating a system in which quantum effects become apparent at high temperatures. Since they exist in semiconductors, these polaritons have a high potential for applica-tion to many solid state systems, especially as their most interesting quantum effects, Bose-Einstein con-densation in particular, become accessible at higher temperatures.
In this thesis, I focus primarily on the effects of injecting electrical current into a polariton condensate. I was able to take advantage of the well-established fabrication methods for GaAs-based systems, as well as the high-quality samples developed by my predecessors, which allow the formation of nearly equilibrium condensates over large areas. My colleagues and I then made devices that allow direct injection of electri-cal charge carriers through polariton condensates in the in-plane direction of the 2D system. I report here three major observations. The first is a superlinear increase in photocurrent, which we attribute to stimula-tion of an Auger-like scattering of excitons into both the condensate and free carrier states. The second is an increase in the condensate density with current injection, which we explain as stimulated pairing of in-jected free electrons with intrinsic free holes. The third effect is a shift in the in-plane momentum of po-lariton condensates with injected current, which is evidence of drag on the polaritons by the free electrons.
In addition to the work with electrical current injection, I also report on exciton transport distances in the polariton system. Specifically, nearly completely excitonic particles are found far from the creation point, with transport distances comparable to those of the much more photonic polaritons. We explain this as an effect of the unusual shape of the polariton energy dispersion.
Electrical Current Injection into Exciton-Polariton Condensates and Polariton-Enhanced Exciton Transport
David W Snoke