# Regensburg 2002 – wissenschaftliches Programm

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# HL: Halbleiterphysik

## HL 43: Si/Ge

### HL 43.3: Vortrag

### Freitag, 15. März 2002, 11:00–11:15, H14

**The neutral Cd-vacancy complex in Si and Ge** — •Nicolae Atodiresei^{1}, Winfried Kromen^{1}, Stefan Blügel^{2}, and Kurt Schroeder^{1} — ^{1}Institut für Festkörperforschung, Forschungszentrum Jülich — ^{2}Universiät Osnabrück

We have calculated the electronic and geometrical structure of the neutral
Cd-vacancy complex in Si and Ge. The calculations were made using the
pseudopotential *ab initio* molecular-dynamics-method
based on the density-functional theory (DFT) in the local density
approximation (LDA). We use the projector-augmented-wave (PAW) method to
describe the scattering properties of Cd in the energy range of the valence
electrons,
Si and Ge are described with soft Kleinman-Bylander pseudopotentials. -
The Cd-vacancy complex was placed in a supercell containing 107 atoms
with c3v-symmetry, and the optimal structure was determined by
total energy and force minimization.
It turns out that the stable configuration is the ’split vacancy’
(Cd in a middle of a bond between two vacant sites). The Si or Ge neighbor
atoms are displaced inward from the ideal positions by around 5% of
the bond length. The highly symmetric Cd-split-vacancy complex is
compatible
with the low electric field gradient experimentally found in Ge
[H.Haesslein, R.Sielemann and Ch.Zistl, Phys. Rev. Lett. **80**, 2626
(1998)]. The substitutional Cd at a nearest neighbor site of a vacancy has
a higher
energy and relaxes directly into the ’split vacancy’ configuration. -
The PAW-method was tested for a great variety of bulk systems like
Cd-metal,
CdO and CdS (cubic and hexagonal forms). All tests show a good
transferability of the generated projector potentials.