  MoS2 is a layered two-dimensional material with strong spin-orbit coupling
and long spin lifetime, which is promising for electronic and spintronic
applications. However, because of its large band gap and small electron
affinity, a considerable Schottky barrier exists between MoS2 and contact
metal, hindering the further study of spin transport and spin injection in
MoS2. Although substantial progress has been made in improving device
performance, the existence of metal-semiconductor Schottky barrier has not yet
been fully understood. Here, we investigate permalloy (Py) contacts to both
multilayer and monolayer MoS2. Ohmic contact is developed between multilayer
MoS2 and Py electrodes with a negative Schottky barrier, which yields a high
field-effect mobility exceeding 55 cm2V-1s-1 at low temperature. Further, by
applying back gate voltage and inserting different thickness of Al2O3 layer
between the metal and monolayer MoS2, we have achieved a good tunability of the
Schottky barrier height (down to zero). These results are important in
improving the performance of MoS2 transistor devices; and it may pave the way
to realize spin transport and spin injection in MoS2.
