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 (TS) 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 TS. The films deposited at low TS (400 °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 °C, a porous surface with irregular-shaped grains was obtained and a substantial reduction of the SHG and THG response was detected. NLO χ(2)eff coefficients one order of magnitude larger than the χ(2)11 component of an α-quartz reference crystal were measured for all ZnO:F thin films. The χ(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 (Eg) of 3.4 eV were evaluated for films deposited under optimal conditions. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)