Interfacial Oxidation Enables Charge-Transfer Contacts and Degenerate n-Doping in Monolayer MoS$_2$

TL;DR

This paper demonstrates that controlled interfacial oxidation of bismuth contacts induces strong n-doping in monolayer MoS$_2$, enabling low-resistance charge-transfer contacts through the formation of a low work function Bi$_2$O$_3$ layer.

Contribution

It introduces interfacial oxidation as a novel method to create efficient charge-transfer contacts and achieve degenerate n-doping in monolayer MoS$_2$, advancing 2D semiconductor device engineering.

Findings

Oxidation of Bi layer leads to strong electron doping of MoS$_2$

Formation of ultrathin β-Bi$_2$O$_3$ layer reduces work function

Interfacial oxidation enhances contact performance in 2D semiconductors

Abstract

High contact resistance remains a central obstacle to the integration of two-dimensional (2D) semiconductors in electronic devices. Recent advances have demonstrated that contact performance can be dramatically improved through interface engineering, including the use of group-V semimetals and charge-transfer contacts based on strong interfacial doping. Here, we show that controlled interfacial oxidation provides an effective route to convert a semimetal contact into a charge-transfer contact that degenerately $n$-dopes single layer MoS$_2$. Using a combination of angle-resolved photoemission spectroscopy, X-ray photoelectron diffraction, low-energy electron diffraction and scanning tunnelling spectroscopy, we demonstrate that putting single layer MoS$_2$ in contact with a pristine Bi layer merely results in weak doping, whereas oxidation of the Bi layer leads to a pronounced occupation of the MoS$_2$ conduction band with an electron density on the order of $10^{13}$~cm$^{-2}$. The cause of this strong electron doping is the fact that an ultrathin $\beta$-Bi$_2$O$_3$ layer forms below the MoS$_2$ and that this has a particularly low work function, thereby acting as an efficient electron donor to MoS$_2$. Interfacial oxidation thus emerges as a powerful design knob for engineering charge-transfer contacts to 2D semiconductors.