Tunable Schottky and ohmic contacts in graphene and Pd3X2Y8(X=P, As; Y=S, Se) monolayer van der Waals heterostructures

To achieve high-performance devices, it is important to reduce the Schottky barrier height and transition from Schottky contact to ohmic contact. This study investigates the effects of interlayer coupling and biaxial strain on the electronic structure and contact characteristics of three van der Waals heterostructures composed of Pd3P2S8, Pd3As2S8, Pd3As2Se8, and graphene (Pd3P2S8/G, Pd3As2S8/G and Pd3As2Se8/G) using first principles. The results show that the Pd3P2S8/G and Pd3As2S8/G interfaces form n-type Schottky contacts with negligible Schottky barrier heights, while the Pd3As2Se8/G interfaces forms ohmic contacts. By changing the interlayer distance between graphene and the Pd3X2Y8 monolayer or applying biaxial strain in the plane, it is possible to effectively modulate the Schottky barrier height and contact type (n-type Schottky or ohmic) at the Pd3X2Y8/G interfaces. The reason for the tunable ohmic contact at the Pd3X2Y8/G interface is explained by analyzing charge transfer. Finally, the carrier concentration in the graphene layer reaches ∼1013 cm−2 level by interlayer distance and biaxial strain engineering. Therefore, the Pd3X2Y8/G van der Waals heterostructure exhibits tunable ohmic contacts, indicating promising applications for graphene-based field-effect transistors in future experiments.