Abstract
Cu2O/ZnO heterojunction was fabricated on porous silicon (PSi) by a two-step electrochemical deposition technique with changing current densities and deposition times, and then the PSi/Cu2O/ZnO nanostructure was systematically investigated. SEM investigation revealed that the morphologies of the ZnO nanostructures were significantly affected by the applied current density but not those of Cu2O nanostructures. It was observed that with the increase of current density from 0.1 to 0.9 mA/cm2, ZnO nanoparticles showed more intense deposition on the surface. In addition, when the deposition time increased from 10 to 80 min, at a constant current density, an intense ZnO accumulation occured on Cu2O structures. XRD analysis showed that both the polycrystallinity and the preferential orientation of ZnO nanostructures change with the deposition time. XRD analysis also revealed that Cu2O nanostructures are mostly in the polycrystalline structure. Several strong Cu2O peaks were observed for less deposition times, but those peaks diminish with increasing deposition time due to ZnO contents. According to XPS analysis, extending the deposition time from 10 to 80 min, the intensity of the Zn peaks increases, whereas the intensity of the Cu peaks decreases, which is verified by the XRD and SEM investigations. It was found from the I-V analysis that the PSi/Cu2O/ZnO samples exhibited rectifying junction and acted as a characteristical p-n heterojunction. Among the chosen experimental parameters, PSi/Cu2O/ZnO samples obtained at 0.5 mA current density and 80 min deposition times have the best junction quality and defect density.