Charge-transfer Contact to a High-Mobility Monolayer Semiconductor

TL;DR

This paper introduces a novel charge-transfer contact method for 2D semiconductors, achieving record-high hole mobility and enabling exploration of quantum phases like Wigner crystals and fractional quantum Hall states.

Contribution

The authors develop a charge-transfer contact architecture that significantly improves contact quality and enables low-density, high-mobility transport measurements in monolayer WSe$_2$.

Findings

Record-high hole mobility of 80,000 cm$^2$/Vs achieved.

Access to low carrier densities down to 1.6×10^{11} cm$^{-2}$.

Observation of quantum phenomena such as metal-insulator transition and fractional quantum Hall effect.

Abstract

Two-dimensional (2D) semiconductors, such as the transition metal dichalcogenides, have demonstrated tremendous promise for the development of highly tunable quantum devices. Realizing this potential requires low-resistance electrical contacts that perform well at low temperatures and low densities where quantum properties are relevant. Here we present a new device architecture for 2D semiconductors that utilizes a charge-transfer layer to achieve large hole doping in the contact region, and implement this technique to measure magneto-transport properties of high-purity monolayer WSe$_2$. We measure a record-high hole mobility of 80,000 cm$^2$/Vs and access channel carrier densities as low as $1.6\times10^{11}$ cm$^{-2}$, an order of magnitude lower than previously achievable. Our ability to realize transparent contact to high-mobility devices at low density enables transport measurement of correlation-driven quantum phases including observation of a low temperature metal-insulator transition in a density and temperature regime where Wigner crystal formation is expected, and observation of the fractional quantum Hall effect under large magnetic fields. The charge transfer contact scheme paves the way for discovery and manipulation of new quantum phenomena in 2D semiconductors and their heterostructures.