Effect of aluminium doping concentration on microstructures, optical and electrical properties of ZnO thin films by spray pyrolysis technique

Abstract

The effect of Al doping on a ZnO thin film, deposited on a glass substrate by spray pyrolysis under ambient atmosphere, is investigated. Zinc acetate and aluminum nitrate were used as precursors for Zn and Al ions, respectively. The Al-doped ZnO thin films, with Al doping contents of 0 at%(undoped), 1at.%, 2at.%, 3at.%, 4at.% and 5at.%, were deposited at 400 C. X-ray diffraction analysis showed that the undoped ZnO exhibited hexagonal wurtzite crystal structure with major diffraction peak along (002) plane and minor peaks of (101) and (103) planes. The relative intensities of the diffraction peaks and the crystallinity decreased with an increase in Al-doping concentration.Surface morphology of the films were investigated by Scanning Electron Microscope (SEM). The morphological analysis showed that the grain size decreased with higher doping concentration. The optical transmittance spectra of the films showed a high transmittance (higher than 80%) within the visible and near infrared wavelength region. The electrical properties were characterized by the four point probe technique. Undoped ZnO films exhibited the highest sheet resistance, while the 2 at% Al-doped ZnO exhibited minimum sheet resistance.