Probing the Relationship between Defects and Enhanced Mobility in MoS2 Monolayers Grown by Mo Foil

TL;DR

This study demonstrates that sulfur vacancies in CVD-grown monolayer MoS2, introduced during growth on Mo foil, create shallow states near the conduction band that enhance electron mobility and conductivity.

Contribution

It provides a simple growth method for MoS2 on Mo foil and links sulfur vacancies to improved electronic transport properties through combined experimental and theoretical analysis.

Findings

MoS2 devices show mobility exceeding 100 cm2V-1s-1.

Sulfur vacancies induce shallow states near the conduction band.

Vacancies increase n-type doping and conductivity.

Abstract

Atomic vacancies, such as chalcogen vacancies in 2D TMDs, are important in changing the host material's electronic structure and transport properties. We present a straightforward one-step method for growing monolayer MoS2 utilizing oxidized Molybdenum (Mo) foil using CVD and delve into the transport properties of as-grown samples. Devices fabricated from these MoS2 sheets exhibit excellent electrical responses, with the standout device achieving mobility exceeding 100 cm2V-1s-1. Structural analysis and optical signatures unveiled the presence of chalcogen defects within these samples. To decipher the influence of inherent defects on the electronic transport properties, we measured low-temperature transport on two distinct sets of devices exhibiting relatively high or low mobilities. Combining the thermally activated transport model with quantum capacitance calculations, we have shown the existence of shallow states near the conduction band, likely attributed to sulfur vacancies within MoS2. These vacancies are responsible for the hopping conduction of electrons in the device channel. Furthermore, our claims were substantiated through low-temperature scanning tunnelling microscopy measurements, which revealed an abundance of isolated and lateral double sulfur vacancies in Mo foil-grown samples. We found that these vacancies increase the density of states near the conduction band, inducing intrinsic n-type doping in the MoS2 channel. Consequently, this elevated conductivity enhances the field-effect mobility of MoS2 transistors. Our study offers insights into chalcogen vacancies in CVD-grown monolayer MoS2 and highlights their beneficial impact on electronic transport properties.