▎ 摘　　要

Constructing van der Waals heterojunctions is an effective way to solve the defects of two-dimensional (2D) material properties. The crystal structure and electronic properties of 2D monolayer GaSSe have been studied using first-principles calculation. Based on density functional theory calculations, we designed two different GaSSe/graphene heterojunctions and computed their electrical and interfacial properties. The calculated results confirm that graphene and GaSSe can maintain the original band structure after compounding, and the interaction between the two layers shows a weak van der Waals effect. The energy band gap of graphene can be opened to 25 meV when the GaSSe/graphene heterojunctions are formed. Graphene can be used as an electrode, and electrons will flow from the graphene layer to the GaSSe channel. Moreover, the interlayer distance and the applied electric field can be adjusted to modulate the Schottky barrier height and the Schottky contact type (n-type and p-type) of GaSSe/graphene heterojunctions. The two different heterojunctions can achieve Schottky contact-type conversion at a layer spacing of 3.00 and 2.70 angstrom, respectively. The position of the Dirac point of GaSSe/graphene heterojunctions will move with the change of the applied electric field. The Dirac point gradually moves towards the semiconductor valence band as the forward electric field of the heterojunctions increases. In addition, the n-type contact formed at the interface of the GaSSe/graphene heterojunctions will be converted into an Ohmic contact when the reverse electric field is about 0.5 eV angstrom(-1). All the theoretical results clarify the fundamental properties of GaSSe/graphene heterojunctions and predict that the GaSSe/graphene heterojunctions can be used to design high-performance field effect transistor devices.