Berlin 2012 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 40: Impurities / Amorphous Semiconductors

HL 40.1: Talk

Tuesday, March 27, 2012, 11:30–11:45, EW 015

The dangling-bond defect in crystalline and amorphous silicon: insights from ab initio calculations of EPR parameters — •Gernot Pfanner, Christoph Freysoldt, and Jörg Neugebauer — Max-Planck Institut für Eisenforschung, Max-Planck Strasse 1, D-40237 Düsseldorf

The efficiency of thin-film a-Si:H solar cells is severely limited by light-induced defects (Staebler-Wronski effect). 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 (db). However, the assignment of the EPR signal to a specific defect structure requires comparison to theoretical models.

Using density-functional theory, we address structure-property relationships by combining systematic studies for idealized db models in c-Si with a statistical analysis of a variety of dbs in a-Si:H supercells. Our studies reveal the influence of the local geometry on sp-hybridization and delocalization. Yet, the structural variability of a-Si:H cannot be captured by these idealized defect models alone. Rather, our calculations indicate that a relatively broad distribution of db-like structures gives rise to the experimental signal supporting a recent re-evaluation of EPR parameters from multi-frequency EPR [1]. Furthermore, to investigate how the stability of the dbs is affected by residual strain fields, we apply external strain to our crystalline and amorphous db models and monitor the evolution of structure and EPR properties.

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[1] M. Fehr (et al.), Phys. Rev. B (in press), http://arxiv.org/abs/1103.5641