Growth and shape transition of small silicon self-interstitial clusters

Abstract

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 $({I}_{n},5\ensuremath{\le}n\ensuremath{\le}16)$ are determined, showing that the compact geometry appears favored when the cluster size is smaller than 10 atoms $(nl10)$. The fourfold-coordinated dodecainterstitial $({I}_{12})$ structure with ${C}_{2h}$ 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 $n=10$.