Ab-initio simulation of self-interstitial in germanium

Density functional theory (DFT) with local density approximation including on-site Coulomb interaction (LDA+U) has been used to calculate the formation energy of the neutral and charged self-interstitial in germanium as a function of the Fermi level. The calculations suggest that the self-interstitial in germanium can exist in four different charge states: 1–, and 0 for the 〈1 1 0〉 split interstitial, 0, 1+, and 2+ for the tetrahedral position. The 〈1 1 0〉 split interstitial acts as an acceptor, while the tetrahedral self-interstitial acts as a double donor. Allowing structural changes of the self-interstitial with the charge state, the existence of a “two-state defect” in low-temperature irradiated p-type Ge can be explained.