Uncovering the Effects of Metal Contacts on Monolayer MoS2

TL;DR

This study systematically investigates how different metal contacts affect the structural and electronic properties of monolayer MoS2, revealing key interactions and effects relevant for optimizing 2D semiconductor devices.

Contribution

It provides a comprehensive analysis of seven metals on MoS2, identifying reactive metals and effects of oxidation and damage, informing better contact design for 2D electronics.

Findings

Al doping increases n-type carrier density without mobility loss

Ag, Au, Ni cause damage to MoS2 during deposition

Ti, Sc, Y react with MoS2, affecting interface stability

Abstract

Metal contacts are a key limiter to the electronic performance of two-dimensional (2D) semiconductor devices. Here we present a comprehensive study of contact interfaces between seven metals (Y, Sc, Ag, Al, Ti, Au, Ni, with work functions from 3.1 to 5.2 eV) and monolayer MoS2 grown by chemical vapor deposition. We evaporate thin metal films onto MoS2 and study the interfaces by Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, and electrical characterization. We uncover that, 1) ultrathin oxidized Al dopes MoS2 n-type (> 2x10^12 1/cm^2) without degrading its mobility, 2) Ag, Au, and Ni deposition causes varying levels of damage to MoS2 (broadening Raman E' peak from <3 1/cm to >6 1/cm), and 3) Ti, Sc, and Y react with MoS2. Reactive metals must be avoided in contacts to monolayer MoS2, but control studies reveal the reaction is mostly limited to the top layer of multilayer films. Finally, we find that 4) thin metals do not significantly strain MoS2, as confirmed by X-ray diffraction. These are important findings for metal contacts to MoS2, and broadly applicable to many other 2D semiconductors.