Non-Linear Electrical Behaviour of ZnO-NiO Composites Prepared by Solid-State Synthesis

Zinc oxide (ZnO) is an intrinsically n-type semiconductor, which forms Schottky junctions with various metals. Understanding the origin and modulating the rectifying behavior of these junctions has been a challenge, especially for polycrystalline ZnO. This work shows that adding p-type nickel oxide (NiO) to a polycrystalline ZnO-silver (Ag) Schottky junction can enhance the current–voltage response. The maximum improvement is seen at around 10 mol.% NiO, beyond which the ohmic behavior of the NiO-Ag interface dominates and the rectification is lowered. The ZnO-NiO composites were prepared by solid-state synthesis, and electrical contacts were made using silver epoxy. X-ray diffraction studies revealed limited solid solubility in both oxide lattices while scanning electron micrographs revealed a non-homogeneous composite microstructure. Photoluminescence spectroscopies characterized defects in the system. Finally, the current–voltage behavior depends on the composite composition and can be explained based on a combination of Schottky and built-in pn-junctions.