Exciton spectrum in atomically thin monolayers: The role of hBN encapsulation

TL;DR

This study models how the thickness of hBN encapsulation affects exciton energies in monolayer WSe2, revealing significant energy shifts for thin layers and saturation at larger thicknesses, impacting optoelectronic applications.

Contribution

It provides a theoretical model for Coulomb potential in S-TMD monolayers with variable hBN encapsulation thickness, highlighting the influence on exciton energies.

Findings

Exciton energies vary significantly with hBN thickness below 30 layers.

Binding energies saturate to bulk hBN values at larger hBN thicknesses.

The model applies to different substrate types, such as hBN and SiO2.

Abstract

The high-quality structures containing semiconducting transition metal dichalcogenides (S-TMDs) monolayer (MLs) required for optical and electrical studies are achieved by their encapsulation in hexagonal BN (hBN) flakes. To examine the effect of hBN thickness in these systems, we consider a model with an S-TMD ML placed between a semi-infinite in the out-of-plane direction substrate and complex top cover layers: a layer of finite thickness, adjacent to the ML, and a semi-infinite in the out-of-plane direction top part. We obtain the expression for the Coulomb potential for such a structure. Using this result, we demonstrate that the energies of excitonic $s$ states in the structure with WSe$_2$ ML change significantly for the top hBN with thickness less than 30 layers for different substrate cases, such as hBN and SiO$_2$. For the larger thickness of the top hBN flake, the binding energies of the excitons are saturated to their values of the bulk hBN limit.