Extension Doping with Low‐Resistance Contacts for P‐Type Monolayer WSe₂ Field‐Effect Transistors

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 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 kΩ µm at 1013 cm−2). The WOxSey‐doped extension exhibits a sheet resistance as low as 10 ± 1 kΩ □−1. Monolayer WSe2 p‐FETs with sub‐50 nm channel lengths reach a maximum drain current of 154 µA µm−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.