Growth and shape transition of small silicon self-interstitial clusters

The growth behavior of small self-interstitial clusters in crystalline Si is presented based on extensive combined Metropolis Monte Carlo, tight-binding molecular dynamics, and density-functional theory calculations. New stable structures for small interstitial clusters (In, 5≤n≤16) are determined, showing that the compact geometry appears favored when the cluster size is smaller than 10 atoms (n<10). The fourfold-coordinated dodecainterstitial (I12) structure with C2h symmetry is identified to serve as an effective nucleation center for larger extended defects. This work provides the first theoretical support for earlier experiments which suggest a shape transition from compact to elongated structures around n=10.