The electronic and structural properties of a self-interstitial were studied using first-principles calculations. As in the case of Si, the lowest-energy configuration was found to be the (110) dumb-bell. However, the equivalent defect in Ge seemed to involve 4 rather than 2 atoms and was here called a kite defect. The formation energy for an interstitial at an hexagonal site was significantly higher in Ge, as compared to Si. It was suggested that this might explain why the vacancy alone contributed to self-diffusion in Ge.

Self-Interstitial Defect in Germanium. A.J.R.da Silva, A.Janotti, A.Fazzio, R.J.Baierle, R.Mota: Physical Review B, 2000, 62[15], 9903-6