Vacancy cluster distributions in He implanted silicon studied by slow positron annihilation spectroscopy

Doppler broadening measurements performed by a slow positron beam on p-type Si samples implanted with He at 20 keV and at a fluence of 5 x 10(15) and 2 x 10(16) cm(-2) are reviewed and discussed. The evolution of the open volume defects distribution was studied as a function of isochronal and isothermal annealing of the samples. In the as implanted samples the majority of the open volume defects produced by implantation was passivated by He. The open volume defects density decreases, reaching a minimum at 250 degrees C. In the 250-650 degrees C temperature range there is an increase-in defects due to the appearance of vacancy clusters. At the higher annealing temperatures (700-900 degrees C) the vacancy clusters disappear only in the samples implanted at 5 x 10(15) cm(-2).