Berlin 2015 – scientific programme

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DS: Fachverband Dünne Schichten

DS 41: Semiconductor substrates: structure, epitaxy and growth (joint session with O)

DS 41.4: Talk

Friday, March 20, 2015, 11:15–11:30, MA 042

Calculated formation energies of charged defects at surfaces from the repeated-slab approach — •Christoph Freysoldt and Jörg Neugebauer — Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf, Germany

Defects play an important role for the electrical, optical, and chemical properties of semiconductor surfaces under realistic conditions. In theory, the relevant structures, i.e., surfaces and point defects, are often simulated in the supercell approach. Yet, supercell calculations suffer from artificial interactions between the repeated images that are absent in the physical situation of interest. This is particularly problematic for formally charged defects because of the slow 1/r decay of the Coulomb interaction. In this contribution, we suggest a correction for the effect from an analysis of the underlying electrostatics. Screening is taken into account right from the beginning to account for potentially complex screening mechanisms. Yet, the universal long-range behavior limits the complexity to a finite range, allowing for simplified screening models in the end. By using a formulation based on charges and screened potentials, direct contact is made to electronic-structure calculations. The approach will be demonstrated for a model defect at the H-terminated Si(111) surface. The analysis reveals that the electric behavior of defects at surfaces depends on two macroscopic parameters (e.g. potential and field far from the surface), rather than one as for bulk point defects. Different choices of boundary conditions in charged surface calculations and extrapolation to arbitrary surface charges will be discussed.