Density Functional Theory-Based Study of Ag/ZnO Schottky Diode

Here, a ZnO thin film was deposited on a silicon substrate. The hexagonal structure of this deposited film was measured by x-ray diffraction and atomic force microscopy (AFM) without further processing, specifically annealing. Density functional theory (DFT) and DFT+U calculations were conducted on ideal ZnO bulk crystal with crystal size a = 3.249 Å and c = 5.207 Å, and an experimental unit cell estimated by x-ray and AFM analysis a = 3.069 Å and c = 5.3156 Å. A vertical Schottky diode with the structure Ag/ZnO/Ti/Al/n-Si(100) was fabricated on the aforementioned deposited film with optimized parameters. The structure showed Schottky behavior without annealing, indicating oxide layer formation at the Ag/ZnO interface. We obtained contradictory results to the experimental Schottky nature for Ag/ZnO when calculating the structure by DFT+U. When the silver oxide work function was used, we found that the current–voltage characteristics of the device simulated using COMSOL Multiphysics were closer to the experimental results, strengthening the hypothesis of dielectric formation at the interface. Finally, we introduced a vertical power diode structure that is not known to date.