Fermi Level Depinning in Two-Dimensional Materials Using a Fluorinated Bilayer Graphene Barrier

TL;DR

This paper demonstrates that fluorinated bilayer graphene can serve as an effective barrier to prevent Fermi level pinning at metal/2D material interfaces, enhancing tunability of Schottky barriers in electronic devices.

Contribution

It introduces a novel method using fluorinated bilayer graphene as a barrier to depin the Fermi level at metal/2D material interfaces, improving device tunability.

Findings

FBLG reduces Schottky barrier height for low-work function metals.

FBLG increases Schottky barrier height for high-work function metals.

FBLG creates an atomically thin dielectric layer for electronic applications.

Abstract

Strong Fermi level pinning (FLP) - often attributed to metal-induced gap states at the interfacial contacts - severely reduces the tunability of the Schottky barrier height of the junction and limits applications of the 2D materials in electronics and optoelectronics. Here, we show that fluorinated bilayer graphene (FBLG) can be used as a barrier to effectively prevent FLP at metal/2D materials interfaces. FLBG can be produced via short exposure (1-3 min) to SF6 plasma that fluorinates only the top layer of a bilayer graphene with covalent C-F bonding, while the bottom layer remains intrinsic, resulting in a band gap opening of about 75 meV. Inserting FBLG between the metallic contacts and a layer of MoS2 reduces the Schottky barrier height dramatically for the low-work function metals (313 and 260 meV for Ti and Cr, respectively) while it increases for the high-work function one ( 160 meV for Pd), corresponding to an improved pinning factor. Our results provide a straightforward method to generate atomically thin dielectrics with applications not only for depinning the Fermi level at metal/transition metal dichalcogenide (TMD) interfaces but also for solving many other problems in electronics and optoelectronics