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

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 two-dimensional (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 material 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 interfaces but also for solving many other problems in electronics and optoelectronics.