  Low-resistivity metal-semiconductor (M-S) contact is one of the urgent
challenges in the research of 2D transition metal dichalcogenides (TMDs). Here,
we report a chloride molecular doping technique which greatly reduces the
contact resistance (Rc) in the few-layer WS2 and MoS2. After doping, the Rc of
WS2 and MoS2 have been decreased to 0.7 kohm*um and 0.5 kohm*um, respectively.
The significant reduction of the Rc is attributed to the achieved high electron
doping density thus significant reduction of Schottky barrier width. As a
proof-ofconcept, high-performance few-layer WS2 field-effect transistors (FETs)
are demonstrated, exhibiting a high drain current of 380 uA/um, an on/off ratio
of 4*106, and a peak field-effect mobility of 60 cm2/V*s. This doping technique
provides a highly viable route to diminish the Rc in TMDs, paving the way for
high-performance 2D nano-electronic devices.
