Preparation and effect of oxygen annealing on the electrical and magnetic properties of epitaxial (0001) Zn sub(1-x) Co sub(x)O thin films

Epitaxial (0001)-oriented Zn sub(1-x)Co sub(x)O ( sub(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 Co super(2+) substituted Zn super(2+) ions were incorporated into the lattice of ZnO in Zn sub(1-x)Co sub(x)O thin films. The electrical properties measurements revealed that the Co concentration had a nonmonotonic influence on the electrical properties of the Zn sub(1-x)Co sub(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 Zn sub(1-x)Co sub(x)O thin films after oxygen annealing at 600 degree under 15 Pa O sub(2) pressure for 60 mins. Room-temperature ferromagnetic was observed and the ferromagnetic Co amount was smaller than the nominal Co concentration for Zn sub(1-x)Co sub(x)O samples before oxygen annealing. After oxygen annealing, the Zn sub(1-x) Co sub(x)O thin films exhibited paramagnetic behavior. It is suggested that the room-temperature ferromagnetic of Zn sub(1-x)Co sub(x)O thin films may attribute to defects or carriers induced mechanism.