Texture Analysis of Thin In 2 O 3 :Sn Films Prepared by Direct-current and Radio-frequency Magnetron-sputtering
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Karola Thiele Universität Göttingen, Institut für Materialphysik, 37073 Göttingen, Germany
Zhaohui Qiao Universität Duisburg-Essen, Fachbereich Physik, Campus Essen, 45117 Essen, Germany (Received 16 March 2005; accepted 25 May 2005)
Thin In2O3:Sn (ITO) films prepared by radio-frequency (rf) or direct-current (dc) magnetron-sputtering and in central or peripheral position relative to the target were characterized by x-ray diffractograms and pole figures. The diffractograms were normalized with the powder diffraction intensities of the target. In the normalized diffractograms, a random texture level and preferred orientations can be distinguished. The pole figures are represented by normalized -scans that are modeled as a sum of Gaussian curves. The centers of the Gaussian curves are consistent with the prominent orientations of the normalized diffractograms. The textures of the rf-sputtered films in the central and the peripheral position are similar, showing strong contributions from (211)-planes. The texture of dc-sputtered samples is dominated by (400) and (411) planes. In the peripheral sample, the distribution of (400)- and (411)-oriented grains is shifted towards the incidence angle of the particle flux and the frequency of the (222)-grains is suppressed below the random texture level. The results are discussed with reference to a model of incorporation of interstitial oxygen into the growing films.
I. INTRODUCTION
Thin films of In2O3:Sn (ITO) are used as transparent electrodes in optoelectronic applications like photovoltaic cells,1 liquid crystal displays,2 antistatic coatings,3 or organic light-emitting diodes.4 They are prepared by a variety of methods with the aim being to achieve a low electrical resistivity and a high transmittance in the visible spectral range.5 If ITO films can be grown with a biaxial texture, they are of interest as a template for the deposition of high-temperature superconductors on polycrystalline substrates.6 ITO films are routinely characterized by x-ray diffractograms spectra. The positions of the diffraction peaks are used to determine the lattice distortion, which is regarded as a measure for the concentration of oxygen on interstitial lattice sites.7 The width of the peaks is used to determine grain size8 or inhomogeneous strain.9 The relative size (amplitude or area) of the peaks with the
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0297 J. Mater. Res., Vol. 20, No. 9, Sep 2005
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largest intensities, (222), (400), (440), and (622), is often used to monitor variations of the process parameters. A standard -2 x-ray diffraction scan detects only grains with Bragg planes parallel to the film plane. In texture analysis, the sample is tilted against the incidence plane of the x-ray beam and rotated around the film normal to get all grains in diffracting position. The resulting intensities are represented by two-dimensional pole figures and interpreted as distri
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