Total-energy calculations were used to study the structures and formation energies of O chains, as models for thermal double-donors. It was found that the first 3 thermal double-donors consisted of one 4-membered ring, plus 1 or 2 adjacent interstitial O atoms. These metastable double-donors formed bistable negative-U systems with corresponding stable, electrically inactive and staggered structures. The other structures which were observed consisted of 4-membered rings plus adjacent interstitial O atoms at both ends. The double-donors with a central so-called di-Y-lid core became energetically competitive with 4-membered ring thermal double-donors only for clusters that contained more than ten O atoms.

Structures of Thermal Double Donors in Silicon M.Pesola, Y.J.Lee, J.Von Boehm, M.Kaukonen, R.M.Nieminen: Physical Review Letters, 2000, 84[23], 5343-6