Tuning of exciton type by environmental screening

TL;DR

This paper presents a theoretical study on how environmental screening and interface properties influence exciton binding energies and electron-hole overlap in 2D material heterostructures, revealing controllable excitonic features.

Contribution

It introduces a variational method within the effective mass approximation to analyze excitons at 2D heterostructure interfaces, accounting for nonabrupt interfaces and environmental effects.

Findings

Interface-bound excitons are favorable only with small interface thickness or high dielectric screening.

Exciton binding energy and e-h overlap are tunable via interface width and dielectric environment.

The model applies to MoS₂/WS₂ heterostructures, highlighting environmental control of excitonic properties.

Abstract

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 MoS$_2$/WS$_2$ heterostructure. The role of nonabrupt interfaces between the materials is accounted for in our model by assuming a W$_x$Mo$_{1-x}$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.