Influence of Stoichiometry on the Optical and Electrical Properties of Chemical Vapor Deposition Derived MoS$_{2}$

TL;DR

This study systematically investigates how varying stoichiometry during CVD growth of monolayer MoS2 affects its optical and electrical properties, revealing tunable characteristics for electronic and optoelectronic applications.

Contribution

It provides a controlled method to modify MoS2 properties through stoichiometry engineering during CVD synthesis, which was previously underexplored.

Findings

Mobility increases with reduced sulfur content.

Photoluminescence becomes non-uniform with stoichiometry changes.

Devices with low sulfur content show negligible hysteresis and near-zero threshold voltage.

Abstract

Ultrathin transition metal dichalcogenides (TMDCs) of Mo and W show great potential for digital electronics and optoelectronic applications. Whereas early studies were limited to mechanically exfoliated flakes, the large-area synthesis of 2D TMDCs has now been realized by chemical vapor deposition (CVD) based on a sulfurization reaction. Since then, the optoelectronic properties of CVD grown monolayer MoS$_{2}$ have been heavily investigated, but the influence of stoichiometry on the electrical and optical properties has been largely overlooked. Here we systematically vary the stoichiometry of monolayer MoS$_{2}$ during CVD via controlled sulfurization and investigate the associated changes in photoluminescence and electrical properties. X-ray photoelectron spectroscopy is employed to measure relative variations in stoichiometry and the persistence of MoO$_{x}$ species. As MoS$_{2-{\delta}}$ is reduced (increasing {\delta}), the field-effect mobility of monolayer transistors increases while the photoluminescence yield becomes non-uniform. Devices fabricated from monolayers with the lowest sulfur content have negligible hysteresis and a threshold voltage of ~0 V. We conclude that the electrical and optical properties of monolayer MoS$_{2}$ crystals can be tuned via stoichiometry engineering to meet the requirements of various applications.