Extension Doping with Low-Resistance Contacts for P-Type Monolayer WSe Field-Effect Transistors.

Source/Drain extension doping is crucial for minimizing the series resistance of the ungated channel and reducing the contact resistance of field-effect transistors (FETs) in complementary metal-oxide-semiconductor (CMOS) technology. 2D semiconductors, such as MoS and WSe, are promising channel materials for beyond-silicon CMOS. A key challenge is to achieve extension doping for 2D monolayer FETs without damaging the atomically thin material. This work demonstrates extension doping with low-resistance contacts for monolayer WSe p-FETs. Self-limiting oxidation transforms a bilayer WSe into a hetero-bilayer of a high-work-function WOSe on a monolayer WSe. Then, damage-free nanolithography defines an undoped nano-channel, preserving the high on-current of WOSe-doped FETs while significantly improving their on/off ratio. The insertion of an amorphous WOSe interlayer under the contacts achieves record-low contact resistances for monolayer WSe over a hole density range of 10 to 10 cm (1.2±0.3 kΩ μm at 10 cm). The WOSe-doped extension exhibits a sheet resistance as low as 10±1 kΩ □. Monolayer WSe p-FETs with sub-50 nm channel lengths reach a maximum drain current of 154 μA μm with an on/off ratio of 10-10. These results define strategies for nanometer-scale selective-area doping in 2D FETs and other 2D architectures.