Atomic defect states in monolayers of MoS$_2$ and WS$_2$

TL;DR

This study investigates how atomic vacancy defects in MoS₂ and WS₂ monolayers affect their electronic properties, revealing defect-induced localized states and potential for doping control, using a tight-binding model with spin-orbit coupling.

Contribution

It provides a detailed theoretical analysis of defect-induced localized states in MoS₂ and WS₂ monolayers, highlighting the roles of different orbitals and defect types, aligning with experimental findings.

Findings

Vacancy defects create localized states in the bandgap.

Metal defects induce p-type doping, sulfur defects induce n-type doping.

Localized states involve metal d and sulfur p orbitals.

Abstract

The influence of atomic vacancy defects at different concentrations on electronic properties of MoS$_2$ and WS$_2$ monolayers is studied by means of Slater-Koster tight-binding model with non-orthogonal $sp^3d^5$ orbitals and including the spin-orbit coupling. The presence of vacancy defects induces localized states in the bandgap of pristine MoS$_2$ and WS$_2$, which have potential to modify the electronic structure of the systems, depending on the type and concentration of the defects. It is shown that although the contribution of metal (Mo or W) $d$ orbitals is dominant in the formation of midgap states, the sulphur $p$ and $d$ orbitals have also considerable contribution in the localized states, when metal defects are introduced. Our results suggest that Mo and W defects can turn the monolayers into p-type semiconductors, while the sulphur defects make the system a n-type semiconductor, in agreement with ab initio results and experimental observations.