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 < 110 > split interstitial, 0,1+, and 2+ for the tetrahedral position. The < 110 > 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. (C) 2008 Elsevier Ltd. All rights reserved.