Oxide structures were formed by evaporating Ni onto ZnO, and annealing in O. The electrical properties of the NiO layer were investigated by means of 4-point probe measurements, and those of the junction were determined performing variable temperature current-voltage measurements. The NiO layers had a maximum room-temperature resistivity of about 100Ωcm after oxidation and a band-gap of 3.5 to 3.6eV. Upon cooling to 75K, the resistivity increased by 6 orders of magnitude. The current-voltage measurements showed that the rectification of the structures was sufficient for deep-level transient spectroscopy. The suitability of this structure for deep-level transient spectroscopic measurements of defects in ZnO at 20 to 390K was demonstrated. The properties of a new shallow level (possibly the H-donor), and a new radiation-induced deep-level defect that might be the O-vacancy, were reported.

Electrical Characterization of NiO/ZnO Structures. F.D.Auret, L.Wu, W.E.Meyer, J.M.Nel, M.J.Legodi, M.Hayes: Physica Status Solidi C, 2004, 1[4], 674-7