Fully encapsulated monolayer WSe₂ tunnel field-effect transistors with ultralow Schottky barriers
Gaurav Pande1*, Jyun-Yan Siao1, Wei-Liang Chen2, Chien-Ju Lee3, Raman Sankar2,4, Yu-Ming Chang2, Chii-Dong Chen4, Wen-Hao Chang3, Fang-Cheng Chou2, Minn-Tsong Lin1,5,6
1Department of Physics, National Taiwan University, Taipei, Taiwan
2Center for condensed matter sciences, National Taiwan University, Taipei, Taiwan
3Department of Electrophysics, National Chiao-Tung University, Hsinchu, Taiwan
4Institute of Physics, Academia Sinica, Nangang, Taipei, Taiwan
5Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan
6Research Center for Applied Sciences, Academia Sinica, Nangang, Taipei, Taiwan
* Presenter:Gaurav Pande, email:gauravpande89@gmail.com
For field-effect transistors (FETs) based on monolayers of two-dimensional semiconducting channels (SC), the most important issues are to ensure the formation of low resistive contacts, 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 WSe₂ FETs by using bi-layer h-BN as a tunnel barrier at the metal/SC interface. We investigate the electrical transport in monolayer WSe₂ FETs with current-in-plane geometry that yields On/Off ratios of the order of 10⁷and hole mobility ~ 38.3 cm²/Vs at 240 K, limited by intrinsic defects in the channel. The contacts involve a ferromagnetic superstructure wherein platinum acts as an immediate metal contact of high work function. We have achieved ultralow effective Schottky barrier heights (~ 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 behaviour of the metal/h-BN/SC/h-BN heterostructures and such control over the barrier height in integration with ferromagnetic tunnel contacts opens up the possibilities for WSe₂-based spintronic devices.

This project is financially sponsored by the Ministry of Science and Technology (MOST 108-2119-M-002-018)

Keywords: monolayer Tungsten diselenide (WSe2), tunnel contacts, bilayer hexagonal Boron Nitride (h-BN), field-effect hole mobility, BN-encapsulation