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Characterization of ZnO structures by optical and X-ray methods

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Abstract

ZnO thin films doped by Ga and In as well as multilayer structures of ZnO/Al2O3 have been investigated by X-ray fluorescence, Raman spectrometry, spectroscopic ellipsometry and vacuum ultra violet reflectometry. Systematic changes in the optical properties have been revealed even for Ga concentrations below 1%. The Raman active phonon mode of Ga doping at 580 cm−1 shows a correlation with the Ga concentration. Optical models with surface nanoroughness correction and different parameterizations of the dielectric function have been investigated. There was a good agreement between the dielectric functions determined by the Herzinger–Johs polynomial parameterization and by direct inversion. It has been shown that the correction of the nanoroughness significantly influences the accuracy of the determination of the layer properties. The band gap and peak amplitude of the imaginary part of the dielectric function corresponding to the excitonic transition changes systematically with the Ga-content and with annealing even for low concentrations.

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... This study is part of a European project, intended to be a step towards the establishment of validated reference methodologies for a reliable characterization of key optoelectronic materials (IND07, "Metrology for the manufacturing of thin films") in the European Metrology Research Program of EURAMET. Furthermore, our investigations aim for the development of reference samples with controlled defect concentration and morphology or methods for elemental depth profiling [9]. ...
... The ellipsometric measurements were used to calculate the film thicknesses of the different layers, because using the reflectometric principle it is possible to calculate only one sample parameter (refractive index, extinction coefficient or thickness). The transparent and opaque photon energy ranges can clearly be distinguished by the interference oscillations characteristic to the transparent range [9] in the ellipsometric measurement. Hence, a simple Cauchy dispersion (n=A+B/λ 2 +C/λ 4 , where n denotes the refractive index, and A, B and C are the Cauchy parameters) using an optical model of c-Si/SiO 2 /ZnO, whereas the refractive index of ZnO can be described by the Cauchy model, was used to calculate the layer thickness and surface nanoroughness from the ellipsometric data. ...
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  • G Jellison
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