Extended Si ˆ311‰ defects

We perform total-energy calculations based on the tight-binding Hamiltonian scheme ~i! to study the structural properties and energetics of the extended $311% defects depending upon their dimensions and interstitial concentrations and ~ii! to find possible mechanisms of interstitial capture by and release from the $311% defects. The generalized orbital-based linear-scaling method implemented on the Cray T3D is used for supercell calculations of large-scale systems containing more than 1000 Si atoms. We investigate the $311% defects systematically from few-interstitial clusters to planar defects. For a given defect configuration, constanttemperature molecular-dynamics simulations are performed 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 interstitial chain structures along the ^011& direction are stable interstitial 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 interstitial chains side by side in the ^233& direction. We find that successive rotations of pairs of atoms in the $011% plane are mechanisms with a relatively small energy barrier for propagation of interstitial chains. These mechanisms, together with the interstitial chain structure, can explain the growth of the $311% defects and related structures such as V-shape bend structures and atomic steps observed in transmission electron microscopy images. @S0163-1829~97!03123-8#