The structures and stability of single silicon interstitials in their neutral state were

investigated via first principles calculations in 3C- and 4H-SiC. By carefully

checking the convergence with Brillouin zone sampling and super-cell size, the

disagreement between previous published results was explained and it was shown

that the split interstitial along the (110) direction, and the tetrahedrally carbon

coordinated structure had competing formation energies in the cubic polytype. A

new migration mechanism for the silicon interstitial in the neutral state was

presented here, and could be important for the evolution of defect populations in

SiC. For 4H-SiC, the most energetically favourable silicon interstitial was found to

be the split interstitial configuration ISisp<110> but situated in the hexagonal layer.

The defect formation energies in 4H-SiC were generally larger than those in 3CSiC;

implying that the insertion of silicon interstitials introduced a large lattice

distortion into the local coordination environments and affected even the secondor

third-nearest neighbours. A comparison was also made between well-converged

plane-wave calculations and calculations involving three localised orbital basis

sets. One of them, in spite of providing a reasonable description of the bulk

properties, was not suitable for describing interstitial defects.

First-Principles Study of Neutral Silicon Interstitials in 3C- and 4H-SiC. T.Liao,

G.Roma, J.Wang: Philosophical Magazine, 2009, 89[26], 2271-84