Interface excitons at lateral heterojunctions in monolayer semiconductors

TL;DR

This paper investigates interface excitons at lateral heterojunctions in monolayer TMDs, revealing their giant binding energies, dependence on band offset, and quantum confinement effects, with implications for optoelectronic device design.

Contribution

It provides a detailed analysis of interface excitons in monolayer TMD heterojunctions, including their binding energies, size, and quantum confinement effects, which were not previously characterized.

Findings

Interface excitons have giant binding energies similar to 2D excitons.

Exciton properties depend strongly on band offset at the junction.

Quantum confinement effects lead to a transition in exciton ground state degeneracy.

Abstract

We study the interface exciton at lateral type II heterojunctions of monolayer transition metal dichalcogenides (TMDs), where the electron and hole prefer to stay at complementary sides of the junction. We find that the 1D interface exciton has giant binding energy in the same order as 2D excitons in pristine monolayer TMDs although the effective radius (electron-hole seperation) of interface exciton is much larger than that of 2D excitons. The binding energy, exciton radius and optical dipole strongly depends on the band offset at the junction. The inter-valley coupling induced by the electron-hole Coulomb exchange interaction and the quantum confinement effect at interface of a closed triangular shape are also investigated. Small triangles realize 0D quantum dot confinement of excitons, and we find a transition from non-degenerate ground state to degenerate ones when the size of the triangle varies. Our findings may facilitate the implementation of the optoelectronic devices based on the lateral heterojunction structures in monolayer semiconductors.