Activation energies for vacancy migration, clustering and annealing in silicon

A series of measurements have been performed at the University of Bath to study the evolution of vacancy-type structures in silicon. Isothermal annealing performed during positron beam-based Doppler broadening measurements have yielded activation energies for vacancy cluster formation and evaporation in silicon of approximately 2.5 and 3.7 eV, respectively. The clusters, which could predominantly be the stable hexavacancy, appear to form between 400-500oC, and anneal at ~ 600oC. A similar technique applied to lowtemperature in situ measurements have yielded the migration energies for the silicon monovacancy and interstitial (of ~ 0.5 and 0.08 eV, respectively). Interesting observations of positronium formation at the surface of the samples studied during isothermal annealing are presented.