Preparation and effect of oxygen annealing on the electrical and magnetic properties of epitaxial (0001) Zn1−x Co x O thin films

Abstract

Epitaxial (0001)-oriented Zn1−x Co x O ( x = 0.01, 0.05 and 0.1) thin films were grown on c-sapphire substrates by pulsed laser deposition. The XRD analysis, optical transmittance and XPS measurements revealed that the Co2+ substituted Zn2+ ions were incorporated into the lattice of ZnO in Zn1−x Co x O thin films. The electrical properties measurements revealed that the Co concentration had a nonmonotonic influence on the electrical properties of the Zn1−x Co x O thin films due to the defects resulted from imperfections induced by Co substitution. The resistivity remarkably increased and the carrier concentration remarkably decreased in Zn1−x Co x O thin films after oxygen annealing at 600 ° under 15 Pa O2 pressure for 60 mins. Room-temperature ferromagnetic was observed and the ferromagnetic Co amount was smaller than the nominal Co concentration for Zn1−x Co x O samples before oxygen annealing. After oxygen annealing, the Zn1−x Co x O thin films exhibited paramagnetic behavior. It is suggested that the room-temperature ferromagnetic of Zn1−x Co x O thin films may attribute to defects or carriers induced mechanism.