  To explore the potential of field-effect transistors (FETs) based on
monolayers of the two-dimensional semiconducting channel(SC) for spintronics,
the two most important issues are to ensure the formation of variable low
resistive tunnel ferromagnetic contacts(FC), and to preserve intrinsic
properties of the SC during fabrication. Large Schottky barriers lead to the
formation of high resistive contacts and methods adopted to control the
barriers often alter the intrinsic properties of the SC. This work aims at
addressing both issues in fully encapsulated monolayer WSe$_2$ FETs by using
bi-layer h-BN as a tunnel barrier at the FC/SC interface. We investigate the
electrical transport in monolayer WSe$_2$ FETs with current-in-plane geometry
that yields hole mobilities $\sim$ 38.3 $cm^{2}V^{-1}s^{-1}$ at 240 K and
On/Off ratios of the order of 10$^7$, limited by the contact regions. We have
achieved ultralow effective Schottky barrier ($\sim$ 5.34 meV) with
encapsulated tunneling device as opposed to a non-encapsulated device in which
the barrier heights are considerably higher. These observations provide an
insight into the electrical behavior of the FC/h-BN/SC/h-BN heterostructures
and such control over the barrier heights opens up the possibilities for
WSe$_2$-based spintronic devices.
