Asymmetric Schottky Contacts in Bilayer MoS2 Field Effect Transistors

TL;DR

This paper investigates the electrical behavior of bilayer MoS2 transistors with Ti Schottky contacts, proposing a model based on asymmetric barriers and demonstrating high photoresponsivity and channel-related hysteresis.

Contribution

It introduces a model explaining high-bias characteristics of bilayer MoS2 transistors with asymmetric Schottky contacts and distinguishes channel effects from interface effects.

Findings

Rectifying junctions with 0.3-0.5 eV Schottky barrier height

High photoresponsivity over 2.5 AW-1

Hysteresis due to MoS2 channel, not interface effects

Abstract

We discuss the high-bias electrical characteristics of back-gated field-effect transistors with CVD-synthesized bilayer MoS2 channel and Ti Schottky contacts. We find that oxidized Ti contacts on MoS2 form rectifying junctions with ~0.3 to 0.5 eV Schottky barrier height. To explain the rectifying output characteristics of the transistors, we propose a model based on two slightly asymmetric back-to-back Schottky barriers, where the highest current arises from image force barrier lowering at the electrically forced junction, while the reverse current is due to Schottky-barrier limited injection at the grounded junction. The device achieves a photo responsivity greater than 2.5 AW-1 under 5 mWcm-2 white-LED light. By comparing two- and four-probe measurements, we demonstrate that the hysteresis and persistent photoconductivity exhibited by the transistor are peculiarities of the MoS2 channel rather than effects of the Ti/MoS2 interface.