Electrical Transport Properties of Single-Layer WS2

TL;DR

This study explores the electronic transport properties of single-layer WS2 transistors, demonstrating high mobility, tunable doping, and potential for advanced electronic and optoelectronic applications.

Contribution

It provides detailed insights into the fabrication, doping control, and transport behavior of single-layer WS2, highlighting its comparable performance to other TMDs and its suitability for future device applications.

Findings

High room-temperature on/off ratio (~10^6)

Mobility up to 140 cm2/Vs at low temperatures

Variable-range hopping in insulating regime

Abstract

We report on the fabrication of field-effect transistors based on single and bilayers of the semiconductor WS2 and the investigation of their electronic transport properties. We find that the doping level strongly depends on the device environment and that long in-situ annealing drastically improves the contact transparency allowing four-terminal measurements to be performed and the pristine properties of the material to be recovered. Our devices show n-type behavior with high room-temperature on/off current ratio of ~106. They show clear metallic behavior at high charge carrier densities and mobilities as high as ~140 cm2/Vs at low temperatures (above 300 cm2/Vs in the case of bi-layers). In the insulating regime, the devices exhibit variable-range hopping, with a localization length of about 2 nm that starts to increase as the Fermi level enters the conduction band. The promising electronic properties of WS2, comparable to those of single-layer MoS2 and WSe2, together with its strong spin-orbit coupling, make it interesting for future applications in electronic, optical and valleytronic devices.