Disentangling the effects of doping, strain and defects in monolayer WS2 by optical spectroscopy

TL;DR

This study uses advanced optical spectroscopy techniques to distinguish the effects of doping, strain, and defects on the optical properties of monolayer WS2, aiding in better material control for optoelectronic applications.

Contribution

The paper introduces a combined hyperspectral imaging and statistical analysis method to disentangle multiple perturbations affecting monolayer WS2's optical properties.

Findings

Differentiated effects of doping, strain, and defects on optical signals.

Found B-exciton energy less sensitive to doping variations.

Provided a new approach for in situ characterization of 2D materials.

Abstract

Monolayers of transition metal dichalcogenides (TMdC) are promising candidates for realization of a new generation of optoelectronic devices. The optical properties of these two-dimensional materials, however, vary from flake to flake, or even across individual flakes, and change over time, all of which makes control of the optoelectronic properties challenging. There are many different perturbations that can alter the optical properties, including charge doping, defects, strain, oxidation, and water intercalation. Identifying which perturbations are present is usually not straightforward and requires multiple measurements using multiple experimental modalities, which presents barriers when attempting to optimise preparation of these materials. Here, we apply highresolution photoluminescence and differential reflectance hyperspectral imaging in situ to CVD-grown WS2 monolayers. By combining these two optical measurements and using a statistical correlation analysis we are able to disentangle three contributions modulating optoelectronic properties of these materials: electron doping, strain and defects. In separating these contributions, we also observe that the B-exciton energy is less sensitive to variations in doping density than A-excitons.