Spectroscopic Ellipsometry Studies of Al Doped ZnO Thin Films Deposited by Ultrasonic Spray Pyrolysis Technique

ZnO and aluminum doped zinc oxide (ZnO:AI) thin films were deposited onto glass substrates using the lowcost ultrasonic spray pyrolysis technique. The films were characterized and the effect of aluminum doping concentration on their optical, electrical, surface and structural properties were investigated as a function of aluminum doping between 0 and 5 at.%. The effects of aluminum dopant on the crystalline structure and orientation of the ZnO films were analyzed by X-ray diffraction (XRD) study. Surface morphology was studied by a scanning electron microscope (SEM) and the effects of the Al doping concentration on the microstructure of the films were investigated. The ZnO:AI thin films present nanosheet structure surface morphology. Atomic force microscope (AFM) images were taken to see the effect of Al doping on surface topography and roughness of ZnO films. Transmission and reflectance spectra have been taken by UV spectrophotometer. Maximum transmittance of 87% in the visible range of wavelength 400-700 nm were observed for the 5% Al doped ZnO film. The optic method was used to obtain the optical band gap values of these films. The optical characteristics for ZnO:AI films were successfully analyzed by spectroscopic ellipsometry (SE) technique using a Cauchy-Urbach dispersion model. The electrical resistivity of the films was measured by a four-point probe method.