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Electronic properties of graphene-ZnO interface: a density functional theory investigation

Electronic properties of graphene/ZnO interface have been theoretically investigated by applying first principles density functional theory calculations. This interface is demonstrated to have interesting electrical, optical and chemical properties and therefore, is employed in different applications. In our investigation the interface between graphene and different ZnO surfaces such as polar Zn-terminated 0001 and O-terminated 000 1 ¯ surfaces as well as nonpolar ( 10 1 ¯ 0 ) surface are considered. Different interface properties such as equilibrium atomic structure, binding energy, charge transfer and band alignment are calculated for these interfaces. The calculated binding energies between graphene and different ZnO surfaces are within the range of van der Waals or physical adsorption. The results clearly reveal the essential role of oxygen density at the interface. The O- and Zn-terminated ZnO surfaces show the lowest and highest binding energies, respectively. The amount of charge transfer and the direction of interfacial dipole are also dominated by the number of oxygen atoms at the graphene/ZnO interface. Calculations for the interfacial band alignment reveal that a high/low density of oxygen atoms at the interface results in a Schottky/Ohmic contact. It is also shown that inducing oxygen vacancies at an oxygen rich interface leads to the lowering of the Schottky barrier.