Pure and Oxidized Ag Substrate Influence on the Phase Transformation and Semiconducting Behaviors of Layered ZnO: A First-Principles Study

Graphitic-like ZnO layers have been experimentally synthesized on metal substrates over the past few years. Nevertheless, the impact of metal substrates on the structural and electric properties of ZnO is still unclear. Utilizing first-principle calculations with van der Waals correction, we found that the phase transformation from graphitic-like to wurtzite structure occurs when the thickness of freestanding ZnO exceeds seven layers. With the presence of pure Ag(111) substrate, the critical transformation thickness decreases to two layers because of the depolarization effect originating from the charge transfer from Ag substrate to ZnO. Band structure analysis displays the semiconducting behaviors for the freestanding graphitic-like ZnO layers. On the pure Ag substrate, monolayer and bilayer ZnO is n-doped by the substrate and a metallic character of ZnO is observed. Importantly, the semiconducting behavior of ZnO layers is maintained when ZnO is in contact with oxidized Ag substrate because of less charge transfer between ZnO and Ag. The metal–semiconductor contact results in a Schottky barrier of 0.8 eV. The simulation findings indicate that the few-layered ZnO on oxidized Ag system possesses potential applications in optoelectronic devices.