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DF: Fachverband Dielektrische Festkörper

DF 6: Optical and nonlinear optical properties, photonic

DF 6.3: Talk

Tuesday, March 15, 2011, 11:20–11:40, MÜL Elch

A microscopic model for diffusive hopping charge transport in wide-bandgap oxide semiconductors — •Christoph Merschjann¹, Mirco Imlau², and Hauke Brüning² — ¹Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Berlin, Germany — ²Universität Osnabrück, Fachbereich Physik, Osnabrück, Germany

Relaxation and recombination processes of optically excited charge carriers in wide-bandgap oxide semiconductor crystals (e.g. niobates, phosphates, borates) often exhibit non-exponential decay shapes. In recent years, such relaxations have been phenomenologically described by stretched exponential functions after Kohlrausch, Williams and Watts (KWW). Although they describe the shapes fairly good, it is not possible to directly retrieve informations about the nature of the relaxation, i.e. the charge-transport process, from the KWW formalism.

We present a novel microscopic model for the diffusive hopping charge transport via strongly localized states (e.g. small polarons). This random-walk-based model directly incorporates microscopic quantities, such as lifetimes of single hopping events, electron and hole densities, and dimensionality of the system under study. We compare our numerical, analytical and experimental results. In the common case of equal electron and hole densities, as found in KNbO₃, our model yields the above named quantities with high accuracy.

Generalizations of our model, as well as relations to the KWW formalism, are discussed in the presentation.