Regensburg 2007 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 46: Poster 2

HL 46.63: Poster

Thursday, March 29, 2007, 15:00–17:30, Poster A

Polaron and phonon properties in WO₃ thin films — •Mario Saenger¹, Thomas Höing², Tino Hofmann¹, and Mathias Schubert¹ — ¹Center for Materials and Nanoscience, Department of Electrical Engineering, University of Nebraska-Lincoln, NE 68588-0511, U.S.A. — ²FLABEG GmbH. und Co. KG, Glasserstr. 1, D-93437, Furth i. Wald, Germany

We report on the evolution of the optical phonon and polaron mode properties in amorphous tungsten oxide thin films by spectroscopic ellipsometry over the infrared to ultraviolet spectral range upon electrochemical proton and electron intercalation. We obtain a quantitative description for the coloration induced optical constants spectra changes by model dielectric function analysis of the intercalated thin films. Upon increased intercalated charge densities we observe the strong polarity reduction of the tungsten-oxygen bending mode, the formation of a distinct vibration band located above the tungsten oxide phonon modes, a strong increase of polarity together with the red shift of the polaron mode, whereas proton- and moisture-related lattice vibration modes remain unaltered. Our experimental results indicate no actual hydrogen incorporation upon intercalation. From the phonon mode changes we suggest that oxygen extraction related defect generation upon intercalation causes the polaron formation, also indicative for tungsten oxidation-state reduction from W⁶⁺ to W⁵⁺. The red shift of the polaron mode can be explained by increase in polaron-polaron interaction, while its amplitude dependance on the intercalated charge density is concordant with the exponential intercalation model