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 WSe 2 using a monolayer dopant, namely tungsten oxyselenide (TOS), that induces degenerate doping densities as high as ∼4 × 10 13 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–WSe 2 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 WSe 2 .