Influence of annealing temperature on the formation and characteristics ofsol-gel prepared ZnO films

ZnO thin films have been obtained by the sol-gel method from a Zn(OOCCH3)(2 ) precursor on soda lime glass and silicon wafer substrates. The films, obt ained by a single dipping procedure, were characterized by Fourier transfor m infrared (FTIR) and ultraviolet-visible (UV-vis) spectroscopies, atomic f orce microscopy, x-ray diffraction and ellipsometry measurements. Thermally untreated and annealed (100-450 degrees C) films were studied in order to analyze the influence of temperature on the formation and properties of the ZnO coatings. Remarkably, these results indicate that ZnO forms at conside rably lower temperatures than 450 degrees C, which is usually considered in the literature as a reference temperature for the formation of ZnO. Thus, a sharp absorption edge of ZnO at similar to 380 nm can be easily observed in the UV-vis spectra of films annealed at 200 and 300 degrees C, according ly, and the FTIR data indicate the absence of organic groups at these tempe ratures. The atomic force microscopy results show a uniform, void-free surf ace of the films, as well as larger grain sizes as the annealing temperatur e is increased. The x-ray diffraction patterns show that the films are poly crystalline and also show evidence of the formation of ZnO at temperatures as low as 200 degrees C. The refractive index values, obtained by ellipsome try, increase with annealing temperature, up to a value of 1.96 for the fil m fired at 450 degrees C. (C) 1999 American Vacuum Society.