Role of precursor material and annealing ambience on the physical properties of SILAR deposited ZnO films

Abstract

ZnO thin films were deposited using a successive ionic layer adsorption and reaction (SILAR) method from three different precursors viz. zinc acetate, zinc sulfate and zinc chloride. All the films were annealed in air and vacuum ambiences at 350°C and characterized for their structural, optical, photoluminescence, electrical and surface morphological properties. The XRD profiles show that the crystalline quality of the films is improved after annealing in both the environments. It is found that the preferential orientation changes from (002) plane to (100) plane after atmospheric annealing for the films prepared from zinc acetate and zinc sulfate precursors, whereas no transition in preferential orientation is observed for films deposited from zinc chloride. Vacuum annealing does not affect the preferential orientation of all the three sets of films, but the intensities of diffraction peaks are increased remarkably. The films fabricated from zinc acetate and zinc sulfate precursors exhibit good average optical transmittance of 80% in the visible region after annealing whereas that deposited from zinc chloride exhibits only 70% transmittance. Compared with as-deposited and air annealed films, the vacuum annealed films exhibit lower electrical resistivity. An increase in the optical band gap and improvement in the surface morphology are also observed after annealing under both the ambiences for all the films, irrespective of the precursor used. The photoluminescence studies support the results on crystalline quality and optical band gap.