Dresden 2009 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 18: Impurities/amorphous semiconductors

HL 18.4: Vortrag

Dienstag, 24. März 2009, 12:45–13:00, POT 151

Ab-initio calculations of hyperfine parameters for various Si-dangling bond models — •Gernot Pfanner, Christoph Freysoldt, and Jörg Neugebauer — Max-Planck Institute for Iron Research, Computational Materials Design, Max-Planck-Strasse 1, D-40237 Duesseldorf

Thin-film silicon solar cells are considered as low-cost successors of bulk crystalline Si solar cells. However, at the moment, their efficiency is severely limited by light-induced defects. The nature of the so-called 'Staebler-Wronski' effect, i.e. light-induced metastable changes in the properties of hydrogenated amorphous silicon, is not yet understood and remains challenging. Electron-paramagnetic resonance (EPR) is a key technique to improve our knowledge about the local atomic structure and, consequently, about the processes causing the long-term drop in the conversion rate and thus in the device performance. However, the interpretation of the EPR spectrum requires theoretical insights in the influence of the microscopic structure on the hyperfine parameters, which we provide by first-principle calculations. For this purpose, we employ density-functional theory and a pseudopotential approach, in which the all-electron wave function is reconstructed from a combination of free-atom and pseudo-wavefunctions. Within this approach, we consider various dangling-bond models and study the sensitivity of the hyperfine parameters to structural features in the vicinity of the defect. A comparison with available experimental data allows us to identify realistic dangling bond models.