Exciton spectrum in atomically thin monolayers: The role of hBN encapsulation
A. O. Slobodeniuk, Maciej R. Molas
Abstract
The high-quality structures containing semiconducting transition-metal dichalcogenide (S-TMD) monolayers (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 a ${\mathrm{WSe}}_{2}$ ML change significantly for the top hBN with thickness less than 30 layers for different substrate cases, such as hBN and ${\mathrm{SiO}}_{2}$. 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.