Electronic, optical, and excitonic properties of atomically thin semiconductors

Atomically thin semiconductors exhibit distinct properties from their bulk counterparts, due to the reduced dimensionality and the quantum confinement effect. In this dissertation, we investigate the electronic, optical, and excitonic properties of atomically thin semiconductor materials using first-principles calculations based on density functional theory and many-body perturbation theory.

The first part of this thesis presentation addresses the intriguing properties of atomically thin gallium nitride (GaN) quantum wells. Due to the extreme quantum confinement effect, deep ultraviolet emission and room-temperature stable excitons can be achieved from GaN. In addition, we propose that the exciton lifetime can be efficiently controlled by the structural engineering. As a result, we show atomically thin GaN has the potential to be used in efficient optoelectronic and excitonic applications.

The second part of this thesis presentation covers the strong excitonic effects in hexagonal boron nitride (h-BN). We reveal that the strong exciton-phonon interaction contributes to the effective indirect optical transitions and the bright luminescence in bulk h-BN. In addition, we demonstrate that monolayer h-BN on Highly Ordered Pyrolytic Graphite (HOPG) exhibit a giant renormalization of the electronic band gap and the exciton binding energy due to the strong screening induced by the HOPG substrate.

Chair: Mackillo Kira

Co-Chair: Emmanouil Kioupakis