Exploring p-Type Contact for Monolayer WS2 FETs Using Halogen Doping and Intermediate Layers

This work presents a density functional theory (DFT) study of substitutional and adsorption-based halogen (I or F) doping of WS<inf>2</inf>-based transistors to enhance their contact properties. Substitutional doping of the WS<inf>2</inf> monolayer with halogens results in n-type behavior, while halogen adsorption on the surface of the WS<inf>2</inf> monolayer induces p-type behavior. This is attributed to differing directions of charge flow, as supported by the Mulliken analysis. However, due to Fermi-level pinning (FLP) at the WS<inf>2</inf>-metal interface, the p-type behavior resulting from halogen adsorption is not very prominent. To achieve better p-type contact, intermediate layers of graphene and h-BN are used to mitigate the FLP effect, showing significant improvement. The F-adsorbed WS<inf>2</inf>-graphene-Pt interface demonstrates excellent p-type contact with a substantial reduction in the hole Schottky barrier height, making it ideal for efficient WS<inf>2</inf>-based p-type MOS transistors in CMOS technology.