Collective states and devices based on indirect excitons in wide-bandgap semiconductor quantum wells

Indirect, or dipolar excitons are bosonic quasi-particles in semiconductors composed of spatially separated but still Coulomb-bound electron and hole. They have long lifetime and can travel over large distances before recombination, offering a unique system that can be both optically active and electrically controllable. It is suitable for studies of fundamental properties of light and matter and for the development of conceptually new excitonic devices. Excitons in polar GaN quantum wells can be considered as naturally indirect excitons, because of the strong built-in electric field in the growth direction. This dissertation describes an experimental realization and investigation of indirect excitons engineered in GaN/(Al,Ga)N heterostructures, and the collective states that these can form. The main results of this work are (i) the demonstration of the in-plane confinement and cooling of indirect excitons, when trapped in the electrostatic potential created by semitransparent electrodes of various shapes carefully designed and deposited on the sample surface, this is a prerequisite for studies of the complex phase diagram of these dipolar bosons at low temperatures; (ii) The proof-of-principle for electrical control of the indirect exciton densities and fluxes in the plane of the heterostructure, which opens attractive prospects for realization of excitonic devices; (iii) the first points on the dipolar boson phase diagram, providing first evidence of the density-induced correlated state (dipolar liquid) and dissociation (Mott transition) of the indirect excitons in GaN/(Al,Ga)N heterostructures. (author)