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 °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 ( E g ) of 3.4 eV were evaluated for films deposited under optimal conditions. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)