The nature of covalent bonding of self-interstitials in silicon.

The microscopic nature of the bonds between a self-interstitial and its neighbors is discussed using a tight binding picture in the extreme covalent limit. This is shown to lead to a simple description of energy level formation and local bonding, in agreement with local density functional calculations for the tetrahedral and hexagonal sites. Moreover a slight extension of the model allows an estimation of formation energies.