Extension Doping with Low‐Resistance Contacts for P‐Type Monolayer WSe<sub>2</sub> Field‐Effect Transistors
Sihan Chen, Yue Zhang, William P. King, Rashid Bashir, Arend M. van der Zande
Abstract
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.