ATOMISTIC STUDY OF THE (001), 90-DEGREES TWIST BOUNDARY IN SILICON

A new type of a structural unit (the <(4)over bar 2m> dreidl) is propo sed on the basis of molecular dynamics simulations for the core model of the (001), 90 degrees twist grain boundary in silicon. The structur al unit resembles a polyhedron in which some edges, not corresponding to bonds between atoms, are absent. The dreidl has the <(4)over bar 2m > (D-2d) point-group symmetry and consists of 14 atoms which form eigh t five-membered rings maintaining tetrahedral bonding in the boundary core. Molecular dynamics simulations with the empirical Tersoff-potent ial were performed to evaluate the energy of the (001), 90 degrees twi st boundary at T = 0 K. The effect of both rigid-body translations par allel to the grain boundary plane and alternative reconstructions invo lving conventional structural units was investigated. Despite the high degree of dimerization the twist boundary was found to have a low ene rgy compared with structural models of twist grain boundaries in silic on previously studied.