Optical signatures of states bound to vacancy defects in monolayer MoS$_2$

TL;DR

This study investigates the optical properties of monolayer MoS$_2$ with vacancy defects, revealing defect-induced resonances in the out-of-plane susceptibility that help identify and characterize vacancy types.

Contribution

It introduces a combined theoretical approach to identify optical signatures of vacancy defects in monolayer MoS$_2$ using density functional theory, tight-binding, and Dirac models.

Findings

Vacancy defects cause resonances in out-of-plane susceptibility within the bandgap.

Different vacancy types produce distinct optical spectra signatures.

The methods enable characterization of vacancy defects via optical measurements.

Abstract

We show that pristine MoS$_2$ single layer (SL) exhibits two bandgaps $E_{g\parallel}=1.9$ eV and $E_{g\perp}=3.2$ eV for the optical in-plane and out-of-plane susceptibilities $\chi_\parallel$ and $\chi_\perp$, respectively. In particular, we show that odd states bound to vacancy defects (VDs) lead to resonances in $\chi_\perp$ inside $E_{g\perp}$ in MoS$_2$ SL with VDs. We use density functional theory, the tight-binding model, and the Dirac equation to study MoS$_2$ SL with three types of VDs: (i) Mo-vacancy, (ii) S$_2$-vacancy, and (iii) 3$\times$MoS$_2$ quantum antidot. The resulting optical spectra identify and characterize the VDs.