Effect of vacuum magnetic annealing on the structural and physical properties of the Ni and Al co-doped ZnO films

Abstract

About 300 nm-thick Zn 0.87Al 0.06Ni 0.07O, Zn 0.83Al 0.06Ni 0.11O and Zn 0.81Al 0.04Ni 0.15O films were deposited on glass substrates at 300 K by co-sputtering ZnO:Al and Ni targets. The films were annealed in vacuum at 673 K for 2 h under a magnetic field of 4.8 × 10 4 A/m applied along the film plane and then were cooled down to room temperature without magnetic field. All the films have a wurtzite structure and consist of thin columnar grains perpendicular to the substrate. The annealing promotes the (002) orientation growth in the film growing direction for the Zn 0.87Al 0.06Ni 0.07O and Zn 0.83Al 0.06Ni 0.11O films as well as the (100) orientation growth for the Zn 0.81Al 0.04Ni 0.15O film. The annealing results in a slight increase in the grain size. A weak Ni diffraction peak was detected for the annealed films with high Ni content. The annealing enhances the room temperature ferromagnetism of the films. A temperature dependence of magnetization confirms that the Curie temperature is above 400 K for the annealed films. The films magnetically annealed exhibit an anisotropic magnetization behavior. The annealed Zn 0.87Al 0.06Ni 0.07O film has the lowest resistivity (8.73 × 10 −3 Ω cm), the highest free electron concentration (1.73 × 10 20 cm − 3 ) and Hall mobility (4.16 cm 2V − 1 s − 1 ). A temperature dependence of the resistivity from 50 K to 300 K reveals that the carrier transport mechanism is Mott's variable range hopping in the low temperature range and thermally activated band conduction in the high temperature range.