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