Strain dependence of electronic transport in semiconducting oxide thin films

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The project aims at unravelling the strain dependence of electron transport in polycrystalline thin films of transparent conductive oxides. This will be studied using thin ZnO and SnO2 films prepared by magnetron sputtering on flexible silicon and glass substrates. The electrical characterisation will be performed as a function of strain by conductivity and Hall effect measurements. Particular attention will be paid to the influence of grain boundaries. How the electronic structure of the grain boundary barrier, which limits electron transport, is modified by strain will be elucidated using temperature dependent Hall effect measurements of samples with variable carrier concentration. The piezoelectric contributions to the grain boundary barriers will be identified by comparing differently textured ZnO films and by comparing ZnO and SnO2 films. Piezoelectric modifications of ZnO Schottky barriers will also be studied using electrical techniques and photoelectron spectroscopy. The project is closely linked to a project of K. Albe in which the electronic structure of ZnO grain boundaries will be calculated, a project of J. Rödel and H.-J. Kleebe in which the mechanical modulation of grain boundaries in ZnO bi- and polycrystals is studied, a project of E. Gjonaj and B.-X. Xu in which the coupling of mechanical and electric fields and their influence on charge transport in polycrystalline ZnO is investigated and a project of J.J. Schneider in which the synthesis and the properties of polarization textured ZnO ceramics are studied.