Giant hydrogen effect on the structure and physical properties of ZnO and Co-doped ZnO films fabricated by the RF magnetron sputtering in Ar + H2 atmosphere

ZnO and Co-doped ZnO films were synthesized by the radio frequency magnetron sputtering in mixed atmosphere of Ar + 20% O₂ and Ar + 20–50% H₂. The morphology, chemical composition, crystal structure, optical transmission, electrical resistance, and magnetic circular dichroism of the films were investigated. It was established that the films thickness decreased several times when Ar was partly replaced by hydrogen in the sputtering chamber. At the same time, for the Co-doped ZnO films, the increase in the relative Co content with the increasing hydrogen concentration was observed. These phenomena are explained by the formation of gaseous ZnH₂ because of the hydrogen reaction with the growing films under the conditions of the high substrate temperature (450 °C) and, respectively, the decrease in the Zn component in the films. The hydrogenated Co-doped ZnO films exhibit an increase in electric conductivity and ferromagnetic behavior at room temperature. The magnetic nature of the films is explained by a combination of the intrinsic ferromagnetism (due to the formation of the Co-H-Co complex) with the inclusion of metallic Co clusters.