EXTENDED SI(311) DEFECTS

We perform total-energy calculations based on the tight-binding Hamilt onian scheme (i) to study the structural properties and energetics of the extended {311} defects depending upon their dimensions and interst itial concentrations and (ii) to find possible mechanisms of interstit ial capture by and release from the {311} defects. The generalized orb ital-based linear-scaling method implemented on the Gray T3D is used f or supercell calculations of large-scale systems containing more than 1000 Si atoms. We investigate the {311} defects systematically from fe w-interstitial clusters to planar defects. For a given defect configur ation, constant-temperature molecular-dynamics simulations are perform ed at 300-600 K for about 1 psec to avoid trapping in the local minima of the atomic structures with small energy barriers. We find that int erstitial chain structures along the [011] direction an stable interst itial defects with respect to isolated interstitials. The interstitial chains provide basic building blocks of the extended {311} defects, i .e., the extended {311} defects are formed by condensation of the inte rstitial chains side by side in the [233] direction. We find that succ essive rotations of pairs of atoms in the {011} plane are mechanisms w ith a relatively small energy barrier for propagation of interstitial chains. These mechanisms, together with the interstitial chain structu re, can explain the growth of the {311} defects and related structures such as V-shape bend structures and atomic steps observed in transmis sion electron microscopy images.