Preparation and effect of oxygen annealing on the electrical and magnetic properties of epitaxial (0001) Zn_1−xCo _xO thin films

Abstract

Epitaxial (0001)-oriented Zn_1−xCo _xO ( _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 Zn_1−xCo _xO thin films. The electrical properties measurements revealed that the Co concentration had a nonmonotonic influence on the electrical properties of the Zn_1−xCo _xO 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_1−xCo _xO 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 Zn_1−xCo _xO samples before oxygen annealing. After oxygen annealing, the Zn_1−xCo _xO thin films exhibited paramagnetic behavior. It is suggested that the room-temperature ferromagnetic of Zn_1−xCo _xO thin films may attribute to defects or carriers induced mechanism.

Keywords

Zn_1−xCo _xO thin film / pulsed laser deposition / oxygen annealing / electrical properties / magnetic property

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