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DS: Fachverband Dünne Schichten
DS 9: Layer Properties: Electrical, Optical, and Mechanical Properties
DS 9.1: Invited Talk
Tuesday, April 1, 2014, 09:30–10:00, CHE 91
Chalcopyrite semiconductors: atomic-scale structure and band gap bowing — •Claudia S. Schnohr1, Stefanie Eckner1, Helena Kämmer1, Tobias Steinbach1, Martin Gnauck1, Andreas Johannes1, Christian A. Kaufmann2, Christiane Stephan2, and Susan Schorr2 — 1Institut für Festkörperphysik, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, 07743 Jena, Germany — 2Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, 14109 Berlin, Germany
Cu(In,Ga)Se2 is one of the most promising material systems for thin film photovoltaics with record efficiencies above 20% on laboratory scale. The material crystallizes in the chalcopyrite type crystal structure where the anion is typically displaced from its ideal lattice site due to the different properties of the neighbouring cations. This subtle structural variation has a strong influence on the energy band gap. Therefore, we have studied the atomic-scale structure of Cu(In,Ga)Se2 as a function of composition using extended X-ray absorption fine structure spectroscopy and valence force field simulations. The local atomic arrangements are found to deviate significantly from the long-range crystallographic structure and the material is characterised by structural inhomogeneity on the atomic scale. Regarding the anion position, two different displacement mechanisms have to be distinguished both of which influence the nonlinear change of the band gap with material composition. Similar results were also obtained for Cu(In,Ga)S2 indicating that our findings represent general features of these highly relevant yet complex chalcopyrite semiconductors.