Defect-induced modification of low-lying excitons and valley selectivity in monolayer transition metal dichalcogenides

TL;DR

This study investigates how chalcogen vacancies in monolayer transition metal dichalcogenides alter their excitonic and valley properties, revealing defect states that influence optical behavior and valley selectivity.

Contribution

It provides a detailed ab initio analysis of defect states and their impact on excitons and valley polarization, offering a pathway for defect engineering in 2D materials.

Findings

Chalcogen vacancies create in-gap and resonant defect states.

Defect states lead to strongly-bound defect excitons.

Valley-selective circular dichroism is reduced by defect hybridization.

Abstract

We study the effect of point-defect chalcogen vacancies on the optical properties of monolayer transition metal dichalcogenides using ab initio GW and Bethe-Salpeter equation calculations. We find that chalcogen vacancies introduce unoccupied in-gap states and occupied resonant defect states within the quasiparticle continuum of the valence band. These defect states give rise to a number of strongly-bound defect excitons and hybridize with excitons of the pristine system, reducing the valley-selective circular dichroism. Our results suggest a pathway to tune spin-valley polarization and other optical properties through defect engineering.