Radio frequency sputtered zinc oxide thin films with application to metal–semiconductor–metal photodetectors

Zinc oxide (ZnO) films were successfully deposited on silicon, silicon dioxide, and glass substrates by radio frequency magnetron sputtering at different deposition conditions. Field emission scanning electron microscopy, X-ray photoelectron spectroscopy, transmission and photoluminescence measurements were employed to analyze the effect of the deposition conditions and the postdeposition annealing treatment on the surface morphology, structure, chemical deposition and optical properties of ZnO thin films. It was found that the thickness of ZnO films decreased with increased ratio of oxygen/argon and increased temperature. The crystalline and stoichiometric quality of the film was improved by depositing at high temperature and low pressure. Crystals formed more tightly and uniformly with heat treatment under air ambient. The dark current of the ZnO metal–semiconductor–metal photodetector was reduced from 3.06 μA to 96.5 nA at 5 V after postdeposition annealing when compared with that of as-deposited ZnO. Its magnitude was found to be at least two orders lower than that of the as-deposited sample.