Electronic and structural properties of germanium self-interstitials

The electronic and structural properties of self-interstitial and self-interstitial-related defects in Ge have been investigated by first-principles calculations. In accordance with previous works we find that the split [110] structure is the most stable energetically, among the self-interstitial defects in Ge. However, in disagreement with previous calculations, we find that the formation energy of the split [110] self-interstitial in Ge is larger than the formation energy of the same defect in Si. Our results differ from previous ones because our calculations are better converged with respect to Brillouin zone sampling. Concerning charged defects, we find that the (+/0) ionization level of the split [110] self-interstitial in Ge is placed at 0.08 eV below the valence-band minimun (VBM), while the (0/-) level is located at 0.37 eV above the VBM. Also, we find that a self-interstitial-related defect, called fourfold-coordinated defect, is stable in Ge with a formation energy of 2.82 eV.