He-vacancy interactions in Si and their influence on bubble formation and evolution

The mechanisms of He bubble and, after annealing, of void formation have been investigated for single and multiple ${\mathrm{He}}^{+}$ implants in Si. Several analytical techniques have been adopted: photoluminescence (PL), Rutherford backscattering of protons, transmission electron microscopy, and atomic force microscopy. When a second implant is performed a systematic enlargement of the bubble band reveals the importance of the interaction between He atoms and point defects generated during irradiation. Size effects of the implanted region protrusions indicated a He diffusion mechanism and an interaction with vacancies and divacancies for the bubble formation. PL spectra indicate the presence of complexes helium divacancies in the same temperature where self-interstitials annihilate at the sample surface. The interaction of helium atoms with divacancies allows the inversion in the vacancy-interstitial balance producing a supersaturation of vacancies in the silicon bulk. This vacancy supersaturation causes the observed annihilation of interstitial type defects after a suitable annealing.