Vacancy-type defects in gas cluster ion-implanted Si were probed by monoenergetic positron beams. The acceleration energy of Ar-ion clusters ranged between 20 – 60 keV, and the mean cluster size was 2×103 atoms. Doppler broadening spectra of the annihilation radiation were measured, and the vacancy-rich region was found to localize at a depth of 0 – 13 nm. Two different defect species were found to coexist in the damaged region introduced by Ar cluster ion implantation, and these were identified as divacancy-type defects and large vacancy clusters filled with Ar (micro gas bubbles). The formation of the vacancy clusters was attributed to extremely high temperature and its rapid transients in impact regions of the cluster ions. The difference between defect species introduced by Ar- and B-ion cluster ion implantation was also discussed.
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