Regensburg 2010 – scientific programme

Parts | Days | Selection | Search | Downloads | Help

HL: Fachverband Halbleiterphysik

HL 36: Ge, GeSi, and Si

HL 36.12: Talk

Wednesday, March 24, 2010, 12:30–12:45, H14

A theoretical study of hyperfine parameters in amorphous silicon — •Gernot Pfanner, Christoph Freysoldt, and Jörg Neugebauer — Department for Computational Material Design, Max-Planck-Institute for Iron Research, Max-Planck-Strasse 1, D-40237 Düsseldorf

Thin-film silicon solar cells are considered as low-cost alternatives to bulk crystalline silicon (c-Si) solar cells. A disadvantage of these devices is that their efficiency is severely limited by defects. The nature of the so-called 'Staebler-Wronski' effect, i.e. light-induced metastable changes in the properties of hydrogenated amorphous silicon (a-Si:H), is not yet fully understood and remains challenging. In this context, electron-paramagnetic resonance (EPR) is a key technique to probe for the local atomic structure of defects with unpaired spins such as the silicon dangling bond. However, the interpretation of the EPR spectrum requires comparison to theoretical calculations. Here, we focus on the hyperfine coupling of the unpaired electron to the nuclear spins. We present ab-initio calculations for a variety of dangling bond models in a-Si:H and consider the results in the light of systematic investigations for the c-Si dangling bond. We show that structural disorder in a-Si:H significantly modifies the trends found for c-Si and discuss whether the model Hamiltonians presently used to extract hyperfine parameters from EPR spectra can capture all relevant effects.