▎ 摘　　要

A Janus MoSSe monolayer, synthesized recently though the chemical vapor deposition method [A. Y. Lu, H. Zhu, J. Xiao, C. P. Chuu, Y. Han, M. H. Chiu, C. C. Cheng, C. W. Yang, K. H. Wei Y. Yang, Y. Wang, D. Sokaras, D. Nordlund, P. Yang, D. A. Muller, M. Y. Chou, X. Zhang and L. J. Li, Nat. Nanotechnol., 2017, 12, 744-749], has drawn considerable attention as a new two-dimensional (2D) material owing to its fascinating electronic and optical properties. In this study, based on first-principles calculations, we systematically explore for the first time the performance of Janus MoSSe monolayers as a channel material contacting with graphene to form van der Waals (vdW) heterostructures. Our calculations show that the intrinsic electronic properties of both the graphene and MoSSe monolayer are preserved well in our proposed two graphene/MoSSe heterostructures (i.e. G/SMoSe and G/SeMoS heterostructures), and n-type Schottky contacts with a small Schottky barrier height (SBH) are formed at their respective interfaces. An analytical model is presented for the barrier heights. Moreover, the n-type Schottky barrier at the G/SMoSe heterostructure interface can be reduced by increasing the interlayer distance and can even be changed to an Ohmic contact by applying a negative electric field. More interestingly, varying the interlayer distance or applying an external electric field can effectively modulate the Schottky barrier and the Schottky contact (n-type and p-type) of the G/SeMoS heterostructure interface. These theoretical findings not only provide insights into the fundamental properties of the graphene/MoSSe interfaces but also open the possibility of designing high-performance field-effect transistors (FETs) based on the graphene/MoSSe heterostructures.