  We report high performance p-type field-effect transistors based on single
layered (thickness, ~0.7 nm) WSe2 as the active channel with chemically doped
source/drain contacts and high-{\kappa} gate dielectrics. The top-gated
monolayer transistors exhibit a high effective hole mobility of ~250 cm2/Vs,
perfect subthreshold swing of ~60 mV/dec, and ION/IOFF of >10^6 at room
temperature. Special attention is given to lowering the contact resistance for
hole injection by using high work function Pd contacts along with degenerate
surface doping of the contacts by patterned NO2 chemisorption on WSe2. The
results here present a promising material system and device architecture for
p-type monolayer transistors with excellent characteristics.
