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High purity n-type silicon single crystal with resistivity in the order of 4000 Ω cm has been irradiated with high-energy oxygen ions at room temperature up to a fluence of 5E15 ions/cm2. The energy of the beam was varied from 3 to 140 MeV using a rotating degrader to achieve a depthwise near-uniform implantation profile. Radiation induced defects and their dynamics have been studied using positron annihilation spectroscopy along with isochronal annealing up to 700 °C in steps of 50 °C for 30 min. After annealing the sample at 200 °C for 30 min, formation of silicon tetravacancies has been noticed. The formation of the tetravacancies was found to be due to agglomeration of divacancies present in the irradiated sample. An experimentally obtained positron lifetime value of 338±10 ps has been reported for silicon tetravacancies, which has a very close agreement with the value obtained from recent theoretical calculations. The tetravacancies were found to dissociate into trivacancy clusters upon further annealing. The trivacancies thus obtained were observed to agglomerate beyond 400 °C to form larger defect clusters. Finally, all the defects were found to anneal out after annealing the sample at 650 °C.

Detector grade n-type float-zone silicon irradiated with 140 MeV O 6+ ions to a dose of 5×1015 particles/cm2 was studied by positron annihilation spectroscopy. Vacancy clusters containing five vacancies were detected in the irradiated sample. Isochronal annealing studies of the irradiated sample reveal the dissociation of five-vacancy clusters and formation of vacancy agglomerates V3, V6 and vacancy-oxygen complexes in the temperature range 250-500 °C. The vacancy-oxygen complexes dissociate at 550 °C and released vacancies agglomerate around 600 °C to form voids comprising 10 vacancies. In the temperature range 600-700 °C, the voids dissociate and around 750 °C advanced vacancy-oxygen complexes VmOn (n>m) form. © 2005 Elsevier B.V. All rights reserved.