Low-Resistance p-Type Ohmic Contacts to Ultrathin WSe₂ by Using a Monolayer Dopant

The high contact resistance to 2D semiconductors must be reduced to attain their full potential for next-generation applications. In this work, we report the lowest total p-type contact resistance (642 Ω·μm) to sub-5 nm thin WSe2 using a monolayer dopant, namely tungsten oxyselenide (TOS), that induces degenerate doping densities as high as ∼4 × 1013 cm–2. Moreover, this doping remains active even at temperatures as low as 77 K, enabling a pathway toward high-quality contacts for low-temperature applications. Electrical measurements taken four months apart on TOS–WSe2 devices kept in ambient conditions show less than an order of magnitude reduction in the hole density and demonstrate promising stability of the doping. In addition, we show a drastic improvement in device characteristics through area-selective doping of the contact, which opens an avenue toward achieving high-performance p-type transistors with ultrathin 2D WSe2.