Berlin 2008 – scientific programme

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SYEC: Symposium Exact-exchange and hybrid functionals meet quasiparticle energy calculations

SYEC 2: Exact-exchange and hybrid functionals meet quasiparticle energy calculations II

SYEC 2.9: Talk

Thursday, February 28, 2008, 16:00–16:15, A 053

Theoretical Spectroscopy of Point Defects in Semiconductors — •M. Bockstedte^1,2, Adam Gali³, A. Marini⁴, A. Rubio¹, and O. Pankratov² — ¹ETSF, Univerisdad del País Vasco UPV/EHU, San Sebastián, Spain — ²Theor. Festkörperphysik, Universität Erlangen-Nürnberg, Erlangen, Germany — ³Department of Atomic Physics, Budapest University of Technology and Economics, Budapest, Hungary — ⁴ETSF, Universit di a Roma Tor Vergata, Roma, Italy

The current theory of point defects in semiconductors is largely based on the density functional theory (DFT) and the local spin density approximation (LSDA). Numerous defect models have been identified with experimental defect centers by predicting quantities related to the defect’s electronic structure. However, there are apparent limitations: the position of localized defect levels is affected by the well-known DFT band gap error and the excited states of defects cannot be assessed rigorously. These two fundamental defect properties are accessible via the many body perturbation theory within the GW-approximation and Bethe-Salpeter equation implemented in the program package SELF. We demonstrate the relevance of this approach for the interpretation of optical experiments for well-identified defect centers. As such we considered the carbon vacancy and di-vacancy in SiC. We show that the observed absorption spectra in contrast to the earlier interpretation also involve resonant levels and the ionization of the vacancy in two different charge states. We discuss the origin of the prominent absorption/photo-luminescence line of the di-vacancy, a common compensation center in semi-insulating SiC.