Bilayer h-BN barriers for tunneling contacts in fully-encapsulated monolayer MoSe2 field-effect transistors

The performance of electronic and spintronic devices based on two-dimensional semiconductors (2D SC) is largely dependent on the quality and resistance of the metal/SC electrical contacts, as well as preservation of the intrinsic properties of the SC channel. Direct metal/SC interaction results in highly resistive contacts due to formation of large Schottky barriers and considerably affects the properties of the 2D SC. In this work, we address these two important issues in monolayer MoSe2 field-effect transistors (FETs). We encapsulate the MoSe2 channel with hexagonal boron nitride (h-BN), using bilayer h-BN at the metal/SC interface. The bilayer h-BN eliminates the metal/MoSe2 chemical interactions, preserves the electrical properties of MoSe2 and reduces the contact resistances by prevention of Fermi-level pinning. We investigate electrical transport in the monolayer MoSe2 FETs that yields close to intrinsic electron mobilities (approximate to 26 cm(2)V(-1)s(-1)) even at room temperature. Moreover, we experimentally study the charge transport through metal/h-BN/MoSe2 tunnel contacts and we explicitly show that the dielectric bilayer of h-BN provides highly efficient gating (tuning the Fermi energy) of the MoSe2 channel at the contact regions even with small biases. Also we provide a theoretical model that allows to understand and reproduce the experimental I-V characteristics of the contacts. These observations give an insight into the electrical behavior of the metal/h-BN/2D SC heterostructure and introduce bilayer h-BN as a suitable choice for high quality tunneling contacts that allows for low energy charge and spin transport.