Exploring <i>p</i>-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 WS₂-based transistors to enhance their contact properties. Substitutional doping of the WS₂ monolayer with halogens results in <i>n</i>-type behavior, while halogen adsorption on the surface of the WS₂ monolayer induces <i>p</i>-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 WS₂-metal interface, the <i>p</i>-type behavior resulting from halogen adsorption is not very prominent. To achieve better <i>p</i>-type contact, intermediate layers of graphene and h-BN are used to mitigate the FLP effect, showing significant improvement. The F-adsorbed WS₂-graphene-Pt interface demonstrates excellent <i>p</i>-type contact with a substantial reduction in the hole Schottky barrier height, making it ideal for efficient WS₂-based <i>p</i>-type MOS transistors in CMOS technology.