We report on the evolution of the polaron and phonon mode properties in amorphous tungsten oxide thin films measured by spectroscopic ellipsometry in the infrared to ultraviolet spectral regions as a function of the intercalated proton density. A parametric physical model dielectric function is presented, which excellently describes the ellipsometry data over a large intercalated charge-density range. Upon increased amounts of intercalated charge we observe a strong increase in the polaron absorption in the visible spectral range, a decrease in the infrared W-O bond polarity, and an increase in the W = O bond polarity. Our findings support the oxygen-extraction model as the polaron formation mechanism in tungsten oxide in agreement with previous theoretical works based on first-principles pseudopotential calculations. We discuss and suggest polaron formation by oxygen-related defect generation as origin for the coloration mechanism in tungsten oxide. We further discuss possible evidence for very large effective mass of the polarons within the insulator-to-metal transition regime.

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We present a parametric dielectric function model in depen‐ dence of the intercalated charge per tungsten ion ratio x, which excellently describes the ellipsometric experimental data, and allows the identification of two polaron modes corresponding to transitions between W4+ and W5+ and between W5+ and W6+ tungsten ion sites. A competitive relation between the two polaron transitions is found. An empirical relation for the amplitude of the polaron transitions is found useful to provide a good description of the polaron transition dependence on x. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Al-doped zinc oxide (ZnO:Al) films were deposited on glass substrates using a reactive midfrequency magnetron sputtering process. The optical transmission and reflection as well as the electrical resistivity of the films prepared on an area of 1000x600 mm(exp 2) were determined at different locations. Films with a uniform distribution of resistivity between 2.9x10(exp -4) and 3.6x10(exp -4) Omega cm and transmittance up to 88% in the visible spectral range were obtained. The ellipsometric spectra of the films were also analyzed using the Drude-Lorentz model. The calculated thicknesses of the films agreed well with those measured by a step profilometer. Secondary neutral mass spectrometry depth profiling showed uniform contents of Zn and O elements, while a slight periodic variation of the Al content was observed at different depths inside the film. A transition zone of 35-55 nm in width between the films and glass substrates due to the interdiffusion was also observed

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