Effects of Vanadium Doping on the Optical Response and Electronic Structure of WS$_{2}$ Monolayers

TL;DR

This study investigates how vanadium doping affects the optical and electronic properties of WS₂ monolayers, revealing tunable electronic features and new photoluminescence behavior through comprehensive broadband optical characterization.

Contribution

First broadband optical characterization of vanadium-doped WS₂ monolayers, demonstrating how doping influences their electronic structure and optical responses.

Findings

Vanadium doping introduces two photoluminescence peaks near the A exciton.

Resonant spectroscopy shows a blueshift in the B exciton with doping.

Band structure sensitivity to Hubbard U correction is observed.

Abstract

Two-dimensional dilute magnetic semiconductors has been recently reported in semiconducting transition metal dichalcogenides by the introduction of spin-polarized transition metal atoms as dopants. This is the case of vanadium-doped WS$_2$ and WSe$_2$ monolayers, which exhibits a ferromagnetic ordering even above room temperature. However, a broadband characterization of their electronic band structure and its dependence on vanadium concentration is still lacking. Therefore, here we perform power-dependent photoluminescence, resonant four-wave mixing, and differential reflectance spectroscopy to study the optical transitions close to the A exciton energy of vanadium-doped WS$_2$ monolayers with distinct concentrations. Instead of a single A exciton peak, vanadium-doped samples exhibit two photoluminescence peaks associated with transitions to occupied and unoccupied bands. Moreover, resonant Raman spectroscopy and resonant second-harmonic generation measurements revealed a blueshift in the B exciton but no energy change in the C exciton as vanadium is introduced in the monolayers. Density functional theory calculations showed that the band structure is sensitive to the Hubbard \(U\) correction for vanadium and several scenarios are proposed to explain the two photoluminescence peaks around the A exciton energy region. Our work provides the first broadband optical characterization of these two-dimensional dilute magnetic semiconductors, shedding light on the novel electronic features of WS$_{2}$ monolayers which are tunable by the vanadium concentration.