Recent ab initio molecular-dynamics simulations have shown that the di-interstitial (I2) and the stable tri-interstitial (I3a) clusters in Si are highly mobile. In these complexes, the two (or three) self-interstitials share a single bond-centered site, a feature which greatly facilitates exchange processes and is responsible for the rapid diffusion. In this contribution, we consider the possibility that the precipitation of self-interstitials results from the clustering of I3 'units' rather than isolated Is. We study the interactions I3+I3→I6 and I6+I3→I9 by bringing an I3 toward either another I3 or I6 along various crystalline directions in 216 host atoms supercells. The calculations show that these reactions occur at a substantial gain in energy and that the stacking along some directions is energetically preferred over others. The I6+I2→I8 reaction leads to a very stable cluster. The results suggest that precipitation mechanisms involving rapidly moving self-interstitial clusters could play an important role in the formation of extended defects.
- Molecular dynamics