Abstract
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(2) and WSe(2), 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(2) p-FETs. Self-limiting oxidation transforms a bilayer WSe(2) into a hetero-bilayer of a high-work-function WO(x)Se(y) on a monolayer WSe(2). Then, damage-free nanolithography defines an undoped nano-channel, preserving the high on-current of WO(x)Se(y)-doped FETs while significantly improving their on/off ratio. The insertion of an amorphous WO(x)Se(y) interlayer under the contacts achieves record-low contact resistances for monolayer WSe(2) over a hole density range of 10(12) to 10(13) cm(-2) (1.2±0.3 kΩ μm at 10(13) cm(-2)). The WO(x)Se(y)-doped extension exhibits a sheet resistance as low as 10±1 kΩ □(-1). Monolayer WSe(2) p-FETs with sub-50 nm channel lengths reach a maximum drain current of 154 μA μm(-1) with an on/off ratio of 10(7)-10(8). These results define strategies for nanometer-scale selective-area doping in 2D FETs and other 2D architectures.