This paper demonstrates the high-quality tunnel barrier characteristics and layer number controlled tunnel resistance of a transition metal dichalcogenide (TMD) measuring just a few monolayers in thickness. Investigation of vertical transport in WS2 and MoS2 TMDs in graphene/TMD/metal heterostructures revealed that WS2 exhibits tunnel barrier characteristics when its thickness is between 2 to 5 monolayers, whereas MoS2 experiences a transition from tunneling to thermionic emission transport with increasing thickness within the same range. Tunnel resistance in a graphene/WS2/metal heterostructure therefore increases exponentially with the number of WS2 layers, revealing the tunnel barrier height of WS2 to be 0.37 eV.
@article{arxiv.1411.4714,
title = {Tunneling transport in a few monolayer-thick WS2/graphene heterojunction},
author = {Takehiro Yamaguchi and Rai Moriya and Yoshihisa Inoue and Sei Morikawa and Satoru Masubuchi and Kenji Watanabe and Takashi Taniguchi and Tomoki Machida},
journal= {arXiv preprint arXiv:1411.4714},
year = {2014}
}