We theoretically investigate the binding energy and electron-hole (e-h) overlap of excitonic states confined at the interface between two-dimensional materials with type-II band alignment, i.e., with lowest conduction and highest valence band edges placed in different materials, arranged in a side-by-side planar heterostructure. We propose a variational procedure within the effective mass approximation to calculate the exciton ground state and apply our model to a monolayer ${\mathrm{MoS}}_2/{\mathrm{WS}}_2$ heterostructure. The role of nonabrupt interfaces between the materials is accounted for in our model by assuming a ${\mathrm{W}}_x{\mathrm{Mo}}_{1-x}{\mathrm{S}}_2$ alloy around the interfacial region. Our results demonstrate that (i) interface-bound excitons are energetically favorable only for small interface thickness and/or for systems under high dielectric screening by the materials surrounding the monolayer, and that (ii) the interface exciton binding energy and its e-h overlap are controllable by the interface width and dielectric environment.

• Received 5 September 2022
• Revised 3 August 2023
• Accepted 16 August 2023

DOI:https://doi.org/10.1103/PhysRevB.108.115303