Fabrication and characterisation of NiO/ZnO structures

Metal-oxide-semiconductor (MOS) structures were formed on n-ZnO and the electrical properties were compared to Au Schottky barrier diodes (SBDs) on similar ZnO. After evaporating Ni onto either ZnO, Si or glass, the thin films were oxidised to produce transparent, resisitive layers. The structure and composition of these layers were studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electron microscopy. The electrical properties were investigated by variable temperature current–voltage (I–V) and four-point probe measurements, whereas the optical properties were investigated by photospectrometry. The influence of oxidation temperature on the resistivity of the nickel oxide layers was used to optimise the processing conditions. NiO layers had a maximum resistivity of approximately 100 Ω cm after oxidation and bandgap of 3.5–3.6 eV at room temperature. The rectifying qualities of the junctions (using Pd gates) were sufficient for DLTS measurements of ZnO in the temperature range 20–390 K.