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

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 WSe2 ML change significantly for the top hBN with thickness less than 30 layers for different substrate cases, such as hBN and SiO2. 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.