ATOMIC-STRUCTURE AND ENERGY OF THE (113) PLANAR INTERSTITIAL DEFECTS IN SI

The atomic structure and energy of the {113} planar interstitial defects in Si have been examined by energy-minimization calculations using the Stillinger-Weber potential, based on the atomic model recently proposed by Takeda from the high-resolution transmission electron microscopy image. The atomic model contains no dangling bonds and consists of the two kinds of structural units characterized by an interstitial atom chain along the [110] direction and by an eight-membered ring. It has been shown from the calculations that the atomic models, in which the arrangement and composition of the two kinds of structural units are similar to the observed structure, can exist stably with relatively small bond-length and bond-angle distortions, and with much smaller energy per interstitial atom than that of the isolated self-interstitial in bulk Si. Through the calculations of models with various composition or arrangement of the structural units, we have elucidated the stability of the eight-membered rings, the mechanism of generation of the {113} defects, the origin of the observed arrangement of the two kinds of structural units, and the mechanism of unfaulting of the {113} defects. It can be said that the {113} planar defects are formed by the sequential generation of the structural units containing the interstitial atom chain side by side on the {113} plane, and the structural units containing the eight-membered ring are inserted separately so as to relax the strain energy of the sequence of the structural units. The unfaulting is the transformation of the sequence of the structural units into the perfect crystal containing additional two net {113} atomic layers under the simultaneous rigid-body translation. It is possible to explain the structure and properties of the {113} planar defects in Si from the viewpoint of the arrangement of the structural units containing no dangling bonds similar to the case of the [110] symmetrical tilt grain boundaries in Si, and without any direct effects of impurities. This is originated from the general nature of covalent crystals which demands that all the atoms are four coordinated.