Effects of fluorine incorporation on the microstructure and optical properties of ZnO thin films synthesized by Sol-gel technique

Abstract

Fluorine doped Zinc oxide (ZnO) [FZO] transparent conducting thin films were deposited by sol-gel spin coating method. Zinc acetate and amonium fluoride were used as precursor solution materials. Microstructural, morphologycal, and optical properties of the films were investigated as a function of flourine (F) doping ranging from 0 to 3.5% mole. From x-ray diffraction (XRD) patterns the films exhibited a hexagonal wurtzite structure with preferred c-axis orientation. All the films had a highly preferential c-axis orientation and exhibited (002) preferential growth in all the dopant ratios. Grain sizes of the films were varied in range of 15 to 18 nm. TheSEM images of the films showed well crystallinity with good homogeneity, smooth surface and uniform grains. The average optical transmittance in the entire visible wavelength region was higher than 95% for all F-doped ZnO except undoped ZnO thin film. The band gap energy values were determined as 3.270, 3.291, 3.293 and 3,287 eV, respectively for undoped ZnO, 0.5, 1.5 and 3.5% mole FZO samples. The band gap values increased with increasing the F dopant concentration for all doped samples. These results make FZO thin films an attractive candidate for transparent material applications. Key words: Flourine doped Zinc oxide (ZnO), Sol-gel growth, transparent conducting oxide (TCO), thin films, microstructures.