Reflectivity in bulk and monolayer crystals of hexagonal boron nitride

Abstract

The growth of high-quality crystals of hexagonal boron nitride (hBN) in 2004 has revealed that hBN is a promising material for light-emitting devices in the deep ultraviolet domain, as illustrated by the demonstration of lasing at 215 nm by accelerated electron excitation, and also the operation of field emitter display-type devices in the deep ultraviolet. Although it was recently understood that hBN is an indirect bandgap semiconductor, the understanding of the optical response close to the bandgap is still an open debate. In hBN, the direct and indirect excitons are close in energy and the dielectric permittivity around 200 nm is expected to be governed by the interplay between direct and indirect transitions. Here I will present our recent reflectivity experiments in high-quality hBN crystals from single monolayer to bulk hBN. I will explain the originality of the dielectric permittivity close to the bandgap of hBN in comparison with other nitride semiconductors.