Structural and physical properties of Ni and Al co-doped ZnO films grown on glass by direct current magnetron co-sputtering

About 200 nm-thick Ni and Al co-doped ZnO films were deposited on glass substrates at 300 and 573 K by co-sputtering ZnO:Al and Ni targets. When the sputtering power applied to the Ni target was adjusted to 11 and 18 W, the Zn0.87Al0.04Ni0.09O film and the Zn0.85Al0.04Ni0.11O film were obtained. All the films have a wurtzite structure and grow mainly with [1 0 0] and [1 1 0] orientations in the growing direction. The films consist of thin columnar grains perpendicular to the substrate. However, the high deposition temperature promotes the grain growth. For the Zn0.87Al0.04Ni0.09O films grown at 300 and 573 K as well as the Zn0.85Al0.04Ni0.11O film grown at 300 K, an optical transmittance increases monotonously from 20% to 60% on increasing the wavelength from 390 to 760 nm. However, the Zn0.85Al0.04Ni0.11O film deposited at 573 K exhibits a flat curve of the transmittance above 50% in the wavelength range of 500-760 nm. The films have an n-type semiconducting behavior at room temperature. The Zn0.85Al0.04Ni0.11O film grown at 573 K has the lowest resistivity (6.9x10-2 Ω cm), the highest free electron concentration (1.0x1020 cm-3) and the lowest Hall mobility (0.87 cm2/V s). The films, except for the Zn0.87Al0.04Ni0.09O film grown at 300 K, have the room temperature ferromagnetism. The Zn0.85Al0.04Ni0.11O film grown at 573 K has the highest saturation magnetization (5.6x10-4 T), a saturation field of 2.5x105 A/m and a coercivity of 8.5x103 A/m.