M. Pesola

Vacancies in SiGe: Jahn–Teller distortion and spin effects

The electronic structure of a vacancy in silicon-germanium is studied using ab initio total-energy minimization methods. The calculations are based on density-functional theory in the local-spin-density approximation. We report ionic relaxations, defect formation energies and ionization levels of Si and Ge vacancies in a zinc blende model structure (SiGe). The Ge vacancy in SiGe is characterized by symmetry-lowering Jahn–Teller (JT) distortions and a negative-effective-U effect, in those respects resembling the vacancy in elemental silicon. For Si vacancy, the exchange-coupling energy is found to overcome the JT energy, and symmetric high-spin ground states are predicted.

Comparison of oxygen-chain models for late thermal double donors in silicon

The electronic and atomic structures of the oxygen chains assigned to late thermal double donors (TDDs) in silicon are studied using accurate total-energy calculations. We find that the ring-type O-chain model is best suited for TDDs and better than the di-Y-lid-type O-chain model. The ring-type O chains have slightly alternating C2v–C1h symmetry consistent with the recent high-field electron paramagnetic resonance experiments. The spin densities of the double-donor states are located outside the region of the O atoms, which makes the hyperfine interaction of an unpaired donor electron with the 17O nuclear spins very weak.

First-Principles Simulation of Oxygen Defects in Silicon

Large-scale electronic structure calculations are used to study structural and electronic properties of oxygen complexes and related defects in Si. Total energies, atomic geometries, charge states, ionization levels and local vibrational modes for the defects are obtained, and their consequences for the thermodynamic and electrical behavior are explored.