The porous nature of ZnO thin films deposited by sol-gel Spin-Coating technique

Zinc oxide (ZnO) thin films were deposited on silicon and quartz substrates, by sol-gel method, using zinc acetate dehydrate [Zn(CH3COO)(2)center dot 2H(2)O] dissolved in isopropanol and glycerol. The structural, morphologic and optical properties of ZnO thin films subsequently annealed at 700 degrees C in air for 30 min have leads to a porous nature of these films. To calculate, the refraction index and the extinction coefficient values, Cauchy formalism is used to evaluate the Spectroscopic Ellipsometry results. Two distinct configurations were proposed for each sample: in the first, the film is considered as mixture of randomly distributed voids and ZnO crystallites while in the second, the effect of porosity gradient is highlighted. This optical analysis gives a better agreement between experiment and theory for a wide range of wavelengths regarding the second configuration.