Low resistance p-type contacts to monolayer WSe₂ through chlorinated solvent doping

Tungsten diselenide (WSe₂) is a promising p-type semiconductor limited by high contact resistance (R_C) and the lack of a reliable doping strategy. Here, we demonstrate that exposing WSe₂ to chloroform provides simple and stable p-type doping. In monolayer WSe₂ transistors with Pd contacts, chloroform increases the maximum hole current by over 100× (>200 µA/µm), reduces R_C to ~ 2.5 kΩ·μm, and retains an on/off ratio of 10¹⁰ at room temperature. These improvements persist for over 8 months, survive a 150 °C thermal anneal, and remain effective down to 10 K, enabling a cryogenic R_C of ~ 1 kΩ·μm. Density functional theory indicates that chloroform strongly physisorbs to WSe₂, inducing hole doping with minimal impact on the electronic states between the valence band and conduction band edges. Auger electron spectroscopy and atomic force microscopy suggest that chloroform intercalates at the WSe₂ interface with the gate oxide, contributing to doping stability and mitigating interfacial dielectric disorder, though further studies are needed to conclusively confirm this mechanism. This robust, scalable approach enables high-yield WSe₂ transistors with good p-type performance.