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HL: Fachverband Halbleiterphysik

HL 13: Theory of electronic structure

HL 13.4: Vortrag

Montag, 25. Februar 2008, 17:00–17:15, EW 202

Charged defects in a supercell formalism: from an empirical to a fully ab-initio treatment of finite-size effects — •Christoph Freysoldt and Jörg Neugebauer — MPI für Eisenforschung, Düsseldorf, Germany

Charged point defects govern the charge carrier densities in semiconductors and are crucial for the performance of electronic devices. However, quantifying the thermodynamical, chemical, electrical, and other properties of such defects is a challenge to both theory and experiment. On the theoretical side, ab-initio calculations have proven to be a valuable tool. In these calculations, the defect is usually modelled in a periodic supercell with a few dozen to a few hundred atoms. Unfortunately, the supercell approximation introduces artificial electrostatic interactions between the charged defects. A number of correction schemes such as Makov-Payne corrections, potential alignment, scaling laws, or Coulomb truncation are available in the literature, but the magnitude of these corrections for a specific supercell usually scatters widely. The assumptions behind these schemes are often unclear and all schemes lack a stringent theoretical foundation. From a formal analysis within linear-response theory, we propose a new and simple scheme that combines the strengthes of Makov-Payne corrections and potential alignment. Our scheme requires no empirical parameters or fitting procedures. Its reliability (scatter in formation energies <0.1 eV, charge transition levels <0.05 eV) is demonstrated for the Ga vacancy in GaAs.