Contact-Induced Semiconductor-to-Metal Transition in Single-Layer WS$_2$

TL;DR

This study demonstrates that atomically precise contacts between single-layer WS$_2$ and Ag(111) induce a semiconductor-to-metal transition, offering a potential pathway for low-resistance contacts in 2D material-based electronics.

Contribution

It reveals that epitaxial growth of WS$_2$ on Ag(111) causes a transition to metallicity, unlike growth on Au(111), and explains this via hybridization with Ag bands.

Findings

WS$_2$ becomes metallic on Ag(111) but remains semiconducting on Au(111).

Metallicity is confirmed by core level photoemission spectra analysis.

DFT calculations attribute the metallic states to hybridization with Ag bands.

Abstract

Low-resistance ohmic contacts are a challenge for electronic devices based on two-dimensional materials. We show that an atomically precise junction between a two-dimensional semiconductor and a metallic contact can lead to a semiconductor-to-metal transition in the two-dimensional material--a finding which points the way to a possible method of achieving low-resistance junctions. Specifically, single-layer WS$_2$ undergoes a semiconductor-to-metal transition when epitaxially grown on Ag(111), while it remains a direct band gap semiconductor on Au(111). The metallicity of the single layer on Ag(111) is established by lineshape analysis of core level photoemission spectra. Angle-resolved photoemission spectroscopy locates the metallic states near the Q point of the WS$_2$ Brillouin zone. Density functional theory calculations show that the metallic states arise from hybridization between Ag bulk bands and the local conduction band minimum of WS$_2$ near the Q point.