Dependence of band structure and exciton properties of encapsulated ${\mathrm{WSe}}_{2}$ monolayers on the hBN-layer thickness

Dependence of band structure and exciton properties of encapsulated ${WSe}_{2}$ monolayers on the hBN-layer thickness

Iann C. Gerber and Xavier Marie

Phys. Rev. B 98, 245126 – Published 19 December 2018

Abstract

The optical properties of two-dimensional transition-metal dichalcogenide monolayers, such as ${MoS}_{2}$ or ${WSe}_{2}$ are dominated by excitons, Coulomb bound electron-hole pairs. Screening effects due to the presence of hexagonal-boron nitride (hBN) surrounding layers have been investigated by solving the Bethe-Salpeter equation on top of $G W$ wave functions in density functional theory calculations. We have calculated the dependence of both the quasiparticle gap and the binding energy of the neutral exciton ground-state $E_{b}$ as a function of the hBN-layer thickness. This paper demonstrates that the effects of screening at this level of theory are more short ranged than is widely believed. The encapsulation of a ${WSe}_{2}$ monolayer by three sheets of hBN ( $\sim 1 nm$ ) already yields a 20% decrease in $E_{b}$ , whereas the maximal reduction is 27% for thick hBN. We have performed similar calculations in the case of a ${WSe}_{2}$ monolayer deposited on stacked hBN layers. These results are compared to the recently proposed quantum electrostatic heterostructure approach.