Excitonic properties of monolayer and bulk hexagonal boron nitride

In this work, we investigate the excitonic properties of monolayer and bulk hexagonal boron nitride (h-BN) based on density functional theory and many-body perturbation theory. Our simulation results indicate 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. Our photoluminescence measurements and reflectance measurements confirm our theoretical prediction on the electronic and optical gap. In addition, we perform first-principles calculations on the exciton-phonon coupling matrix elements and reveal that the strong exciton-phonon interaction contributes to the effective indirect optical transitions and the bright luminescence in h-BN. As a result, we propose that both the strong screening from the substrate and the strong exciton-phonon interaction within h-BN should be considered as an important factor for exciton engineering in h-BN. The work is supported by the University of Michigan College of Engineering Blue Sky Research Program. W.L. was partially supported by the Kwanjeong Educational Foundation Scholarship. Computational resources were provided by the DOE NERSC facility.