Self-interstitial bonding configurations in GaAs and Si

The charge-state-dependent stable and low-energy metastable states of self-interstitial defects in GaAs and Si are identified via self-consistent pseudopotential calculations. An unconventional type of 〈110〉-split-interstitial configuration in which there is essentially no bonding between the split interstitials is found to play an important role in determining the ground-state properties of interstitials for several charge states. Self-interstitials in GaAs are found to be ``negative-U'' defects. They are characterized by effective U's of -0.2 eV for Ga and -0.7 eV for As interstitials. The large negative-U value for As interstitials may explain why no magnetic resonance identification of As interstitials has been achieved in GaAs.