Contact Engineering High Performance n-Type MoTe2 Transistors

TL;DR

This paper reports the development of high-performance unipolar n-type MoTe2 transistors with optimized contacts, achieving record saturation currents and low contact resistance, advancing 2D material electronics.

Contribution

It introduces a contact engineering approach using Ag contacts, AlOx encapsulation, and MIS contacts with h-BN to achieve high-performance n-type MoTe2 transistors.

Findings

Achieved high saturation current (>400 μA/μm at 80 K)

Reduced contact resistance to 1.2-2 kΩ·μm from 80 to 300 K

Identified interfacial metal-Te compounds as dominant contact resistance factors

Abstract

Semiconducting MoTe2 is one of the few two-dimensional (2D) materials with a moderate band gap, similar to silicon. However, this material remains under-explored for 2D electronics due to ambient instability and predominantly p-type Fermi level pinning at contacts. Here, we demonstrate unipolar n-type MoTe2 transistors with the highest performance to date, including high saturation current (>400 ${\mu}A/{\mu}m$ at 80 K and >200 ${\mu}A/{\mu}m$ at 300 K) and relatively low contact resistance (1.2 to 2 $k{\Omega}\cdot{\mu}m$ from 80 to 300 K), achieved with Ag contacts and AlOx encapsulation. We also investigate other contact metals, extracting their Schottky barrier heights using an analytic subthreshold model. High-resolution X-ray photoelectron spectroscopy reveals that interfacial metal-Te compounds dominate the contact resistance. Among the metals studied, Sc has the lowest work function but is the most reactive, which we counter by inserting monolayer h-BN between MoTe2 and Sc. These metal-insulator-semiconductor (MIS) contacts partly de-pin the metal Fermi level and lead to the smallest Schottky barrier for electron injection. Overall, this work improves our understanding of n-type contacts to 2D materials, an important advance for low-power electronics.