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TT: Tiefe Temperaturen

TT 8: Posters Transport

TT 8.4: Poster

Freitag, 4. März 2005, 14:00–18:00, Poster TU C

Percolative Transport in Ag_2+δSe with High Silver Excess — •M. von Kreutzbruck¹, K. Allweins¹, B. Mogwitz², C. Korte², J. Janek², and L. Kienle³ — ¹Institut für Angewandte Physik, Justus-Liebig-Universität Giessen, Heinrich-Buff-Ring 16, D-35392 Giessen — ²Physikalisch-Chemisches Institut, Justus-Liebig-Universität Giessen, Heinrich-Buff-Ring 58, D-35392 Giessen — ³Max-Planck-Institut für Festkörperforschung, Heisenbergstraße 1, D-70569 Stuttgart

Since the appearance of an unusual linear and large magnetoresistance (MR) effect in the narrow gap silver chalcogenides Ag_2+δSe and Ag_2+δTe shown by Xu et al. in 1997 research has drawn much attention to establish new routes for the design of magnetoresistive sensors. We investigated the galvanomagnetic transport properties of polycrystalline Ag_xSe thin films with silver excess in the range from x=1.5 to 18. The results prove that the silver excess controls the transition from linear magnetoresistance (MR) behaviour to the quadratic ordinary MR and the temperature for the metal-semiconductor transition. We observe for 2<x<2.3 a steep rise of the conductivity and interpret this result as a consequence of the percolation of nanoscale silver networks within the semiconducting matrix. To verify our model we performed an estimation on the basis of a FEM-model of both cubic silver selenide grains with nanoscopic silver films in the grain boundary and silver precipitates within the narrowband matrix. The simulation proves the presence of the coexistence of silver paths on the nanoscale and single silver precipitates, which is also indicated by first TEM investigations.