Band-gap Narrowing in ZnO Thick Films by Hf/In Doping

Zinc oxide plays an important role in current industry due to its special characteristics such as low electron conductivity, anti-corrosion, anti-bacteria, and excellent optical and sensing properties. Therefore, thick films of undoped ZnO and Hf/In-doped ZnO were synthesized by screen-printing method. The microstructural and optical properties of prepared films were studied in order to study the effects of variation in dopant ions, dopant concentration, and annealing temperature. Microstructural studies carried out by X-ray diffraction analysis revealed the hexagonal ZnO formation at 300 ∘ C. Enhancement in annealing temperature from 300 ∘ C to 500 ∘ C significantly increased the crystallite size and affected the lattice strains. The doping of Hf as well as In both induced microstructural changes by improving the preferential orientation of crystallinity. The increase in doping concentration enhanced the crystallite size of ZnO, which in turn induced the band-gap narrowing.