Ni-doped ZnO films deposited by RF magnetron sputtering using raw powder target

Pure and nickel-doped zinc oxide thin films were deposited by radio-frequency magnetron sputtering on glass substrates at room temperature using raw powder targets. The dopant concentration was varied from 0 to 4 wt%. Structural characterization of the samples performed with X-ray diffraction confirmed that all films exhibit the hexagonal wurtzite crystal structure with (002) preferred orientation. The average transmittance of all the films is higher than 80% in the visible wavelength region. PL analysis revealed that the ultraviolet emission intensity decreased and exhibited a redshift with increasing Ni concentration. This was consistent with the energy band values (3.35-3.28). A lowest electrical resistivity of 8.42×10⁻⁴ Ω cm was observed for the pure ZnO films, and by increasing Ni content, the electrical resistivity increases, which was subsequently affected by a decrease in charge carrier concentration. AC and DC conductivities were studied to explore the conduction mechanism. The temperature dependence of both ac conductivity and the parameter s is reasonably well interpreted by the correlated barrier hopping model. Activation energy values deduced from both dc conductivity and relaxation frequency are in the range of 0.49-0.61 eV. The analysis of the parameter s leads to the barrier height W_m values which are in agreement with that proposed by the theory of hopping of charge carriers over the potential barrier between the defect states in the band tail as suggested by Elliott. (author)