Structural, morphological, optical, and nonlinear optical properties of fluorine-doped zinc oxide thin films deposited on glass substrates by the chemical spray technique

Fluorine-doped zinc oxide thin films (ZnO:F) were deposited on sodocalcic glass substrates from an aged solution using a chemical spray technique. The effect of substrate temperature (T-s) on the morphological, optical, and nonlinear optical (NLO) properties of the ZnO:F thin films was studied. These films were analysed using X-ray diffraction, scanning electron microscopy, profilometry, optical transmittance, optical fluorescence, and second (SHG) and third harmonic generation (THG) techniques. A polycrystalline structure with a preferential growth along the ZnO(002) plane was found in all cases, with a corresponding average crystal size of less than 32 nm for the films. The morphology of the surfaces and some optical properties were found to be dependent on T-s. The films deposited at low T-s (400 degrees C) showed a uniform surface covered with needle-like grains as well as SHG and THG response. In contrast, for the films deposited at 525 degrees C, a porous surface with irregular-shaped grains was obtained and a substantial reduction chi((2)) of the SHG and THG response was detected. NLO chi((2))(eff) coefficients one order of magnitude larger than the chi((2))(11) component of an alpha-quartz reference crystal were measured for all ZnO:F thin films. The chi((3)) values of the samples, under resonant conditions, were in the interesting range of 10(-12) esu. Finally, a typical optical transmittance higher than 85% and a band gap (E.) of 3.4 eV were evaluated for films deposited under optimal conditions. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.