Effects of vapor annealing on the properties of the ZnO films prepared by spray pyrolysis

Zinc oxide (ZnO) films were deposited on (0 0 0 1) sapphire substrates from a solution containing zinc acetate. The films were deposited in a vertical type hot wall reactor by the pyrolysis of an aerosol produced by an ultrasonic generator. To increase the resistivity of the films, copper doping and annealing in an ambient of water vapor (vapor annealing) were carried out. The resistivity of a 0.5 wt % copper doped ZnO film was around 24 Ω cm. The vapor annealing resulted in a 107-fold increase in the resistivity. After annealing, the crystallinity of the films was improved, as determined by X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). All the films annealed at 600°C for 2 h exhibited a strong (0 0 2) orientation with a smooth surface The crystallinity, surface morphology, composition and electrical properties of the as-deposited and vapor-annealed films were investigated.