  The electrical contact to two-dimensional (2D)-semiconductor materials are
decisive to the electronic performance of 2D-semiconductor field-effect devices
(FEDs). The presence of a Schottky barrier often leads to a large contact
resistance, which seriously limits the channel conductance and carrier mobility
measured in a two-terminal geometry. In contrast, ohmic contact is desirable
and can be achieved by the presence of a nonrectifying or tunneling barrier.
Here, we demonstrate that an nonrectifying barrier can be realized by
contacting indium (In), a low work function metal, with layered InSe because of
a favorable band alignment at the In-InSe interface. The nonrectifying barrier
is manifested by ohmic contact behavior at T=2 K and a low barrier height,
{\Phi}$_B$=50 meV. This ohmic contact enables demonstration of an ON-current as
large as 410 {\mu}A/{\mu}m, which is among the highest values achieved in FEDs
based on layered semiconductors. A high electron mobility of 3,700 and 1,000
cm$^2$/Vs is achieved with the two-terminal In-InSe FEDs at T=2 K and room
temperature, respectively, which can be attributed to enhanced quality of both
conduction channel and the contacts. The improvement in the contact quality is
further proven by an X-ray photoelectron spectroscopy study, which suggests
that a reduction effect occurs at the In-InSe interface. The demonstration of
high-performance In-InSe FEDs indicates a viable interface engineering method
for next-generation, 2D-semiconductor-based electronics.
