Observation of vacancy clustering in FZ-Si crystals during in situ electron irradiation in a high voltage electron microscope

Vacancy accumulation in pure FZ-Si crystals covered with thin Si3N4 films leads upon irradiation with a high intensity electron beam in a high voltage electron microscope (HVEM) at temperatures between 20 and 250 degrees C, to the suppression of the formation of {113}-defects of interstitial type in the central part of the irradiated area. Very small secondary clusters of interstitial type with a density of about 10(11) cm(-2) appear, however, in this area after prolonged irradiation. Small stacking fault tetrahedra and Frank loops of vacancy type connected with interstitial clusters were analysed on an atomic scale in the thinnest part of the irradiated area in a 400 keV high resolution electron microscope. Vacancy clusters might act as nucleation centres for the observed secondary defect formation.