Ab-initio calculations for electronic and optical properties of Er$_{\rm W}$ defects in tungsten disulfide

TL;DR

This study uses ab-initio calculations to explore how Erbium substitutional defects in tungsten disulfide influence its electronic structure and optical absorption, revealing defect-induced localized states and specific optical transitions.

Contribution

It provides a detailed analysis of defect-induced localized states and optical transitions in WS2 with Er defects, including group theory-based selection rules for optical absorption.

Findings

Localized defect states due to Er f-orbitals in WS2

Sharp optical absorption transitions at specific wavelengths

Group theory derivation of optical selection rules

Abstract

Ab-initio calculations for the electronic and optical properties of single-layer (SL) tungsten disulfide (WS$_2$) in the presence of substitutional Erbium defects (Er$_{\rm W}$) are presented, where the W atom is replaced by an Er atom. Defects usually play an important role in tailoring electronic and optical properties of semiconductors. We show that neutral Er defects lead to localized defect states (LDS) in the band structure due to the f-orbital states of Er, which in turn give rise to sharp transitions in in-plane and out-of-plane optical absorption spectra, $\alpha_{\parallel}$ and $\alpha_{\perp}$. We identify the optical transitions at 3 $\mu$m, 1.5 $\mu$m, 1.2 $\mu$m, 920 nm, 780 nm, 660 nm, and 550 nm to originate from Er$_{\rm W}$ defect states. In order to provide a clear description of the optical absorption spectra, we use group theory to derive the optical selection rules between LDS for both $\alpha_{\parallel}$ and $\alpha_{\perp}$.