  High contact resistance is one of the primary concerns for electronic device
applications of two-dimensional (2D) layered semiconductors. Here, we explore
the enhanced carrier transport through metal-semiconductor interfaces in WS2
field effect transistors (FETs) by introducing a typical transition metal, Cu,
with two different doping strategies: (i) a "generalized" Cu doping by using
randomly distributed Cu atoms along the channel and (ii) a "localized" Cu
doping by adapting an ultrathin Cu layer at the metal-semiconductor interface.
Compared to the pristine WS2 FETs, both the generalized Cu atomic dopant and
localized Cu contact decoration can provide a Schottky-to-Ohmic contact
transition owing to the reduced contact resistances by 1 - 3 orders of
magnitude, and consequently elevate electron mobilities by 5 - 7 times higher.
Our work demonstrates that the introduction of transition metal can be an
efficient and reliable technique to enhance the carrier transport and device
performance in 2D TMD FETs.
