Extension Doping with Low-Resistance Contacts for P-Type Monolayer WSe2 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 MoS2 and WSe2, 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 WSe2 p-FETs. Self-limiting oxidation transforms a bilayer WSe2 into a hetero-bilayer of a high-work-function WOxSey on a monolayer WSe2. Then, damage-free nanolithography defines an undoped nano-channel, preserving the high on-current of WOxSey-doped FETs while significantly improving their on/off ratio. The insertion of an amorphous WOxSey interlayer under the contacts achieves record-low contact resistances for monolayer WSe2 over a hole density range of 1012 to 1013 cm-2 (1.2 +/- 0.3 k Omega mu m at 1013 cm-2). The WOxSey-doped extension exhibits a sheet resistance as low as 10 +/- 1 k Omega square-1. Monolayer WSe2 p-FETs with sub-50 nm channel lengths reach a maximum drain current of 154 mu A mu m-1 with an on/off ratio of 107-108. These results define strategies for nanometer-scale selective-area doping in 2D FETs and other 2D architectures.