Optimization and characterization of NiO thin film and the influence of thickness on the electrical properties of n-ZnO nanorods/p-NiO heterojunction

In this study, we report on the synthesis optimization of NiO thin film to grow preferentially along the (111) direction. The x-ray diffraction (XRD) pattern revealed that the NiO film with 200 nm thickness annealed at 600 degrees C temperature has the best preferential orientation along the (111) direction. Also, atomic force microscope (AFM) images show that the grain size of NiO increases at higher temperatures. Then, ZnO nanorods were grown on the NiO thin film with 100, 200 and 300 nm thickness grown at 600 degrees C. The XRD pattern and scanning electron microscope (SEM) images indicate that the well-aligned ZnO nanorods with hexagonal face have a preferential orientation along the c-axis (002). The current voltage measurements of the n-ZnO nanorods/p-NiO heterojunctions showed a clear rectifying behavior for all diodes. The threshold voltage of the heterojunctions was increased by increasing the thickness of the NiO thin film which was attributed to the increasing of the series resistance (R-s) of the diodes.