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, a disagreement between previous published results was explained and it was shown that the split interstitial along 〈110〉 direction and 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, which 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 are, in general, larger than those in 3C-SiC, implying that the insertion of silicon interstitial introduces a large lattice distortion to the local coordination environments and affects even the second- or third-nearest neighbours. A comparison was 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 for bulk properties, was clearly 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