Is gold in silicon a negative-U centre?
CIC nanoGUNE Seminars
- Speaker
-
Fabiano Corsetti, nanoGUNE
- When
-
2012/01/30
12:00 - Place
- nanoGUNE seminar room, Tolosa Hiribidea 76, Donostia - San Sebastian
- Add to calendar
- iCal
It is well-known that the simulation of defects in bulk material presents a
challenge for first-principles methods, as the disruption caused by the defect
centre on the crystalline lattice can be extremely long-ranged. We first
investigate and systematically quantify the various contributions to the total
finite size error for the silicon vacancy in density-functional theory,
focussing on spurious electrostatic interactions, elastic interactions and
wavefunction orthogonality constraints between periodic images of the defect
centre; our calculations demonstrate that the defect formation energy and
stable charge state transition levels exhibit different convergence behaviour
with respect to supercell size, depending on the Brillouin zone sampling used.
We then apply the insights obtained from the vacancy to the study of gold in
silicon, a defect of long-standing technological importance, which has not yet
been well-characterised by modern first-principles methods. We argue that
careful consideration of finite size effects is crucial for obtaining the
correct behaviour of the system, and show that in the dilute limit the defect
becomes a non-spin-polarised negative-U centre due to the effect of Jahn-
Teller distortion. The resulting stable charge state transition levels are in
excellent agreement with the donor and acceptor levels measured
experimentally, and therefore allow for a clear identification of these
levels; furthermore, our results suggest that the assumption used in previous
studies on the nature of the two experimental levels is incorrect.