Characteristics of Al-doped ZnO:Ni films grown on glass by sol-gel dip coating technique

Al-doped NiZnO thin films were fabricated by dip coating and annealed at various temperatures (250-550 °C) and their properties were evaluated. With increasing annealing temperature, the Al contents in the thin films were continually increased, because of the rapid increase in the incorporation efficiency of the Al-O layer with respect to the NiZn-O layer. Polycrystalline nature of the thin films was confirmed by the X-ray diffraction technique. All films have a perfect wurtzite structure without any recordable variation in the ZnO lattice produced by replacing Zn with Ni and Al. The absorption edge shifted to a higher wavelength (red shift) with the increase of annealing temperature indicating that the shrinkage of the optical band gap was induced. The optical band gaps of thin films decreased from 3.5 to 2.5 eV. All films showed ferromagnetic behavior. The annealing process provided a reduced resistivity due to the improved crystal structure of films.