Tuning the Schottky barrier height in graphene/monolayer-GeI2 van der Waals heterostructure

We use first-principles simulations to investigate the structural and electronic properties of a heterostructure formed by graphene and monolayer GeI2 (m-GeI2). While graphene has been extensively studied in the last 15 years, m-GeI2 has been recently proposed to be a stable 2D semiconductor with a wide-band gap, Liu et al (2018 J. Phys. Chem. C 122 22137). By staking both structures we obtain a metal-semiconductor junction, with great potential for applications in the designing of new (opto)electronic devices. The results show that the graphene Dirac cone is preserved in the graphene/m-GeI2 heterostructure. We find that there are no chemical bonds at the graphene and m-GeI2 interface, thus the heterostructure interactions are ruled by van der Waals (vdW) forces. The interface between graphene and m-GeI2 results in a n-type Schottky contact. Furthermore, we show that a transition from n-type to p-type Schottky contact can be obtained by decreasing the interlayer distance. We also modulated the Schottky barrier heights by applying a perpendicular external electric field through the vdW heterostructure. In particular, positive values resulted in an increase of the n-type Schottky barrier height, while negative electric field values induced a transition from n-type to p-type Schottky contact. From our results, we show that m-GeI2 is an interesting material to design new electronic Schottky devices based on graphene vdW heterostructures.