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We implanted n-type silicon with 1.6 MeV helium at fluences ranging from 1×1016 to 1×1017 He/cm2 while keeping a constant dose rate. These samples were then subjected to 800 °C annealing for 30 min. The results obtained by means of cross-sectional transmission electron microscopy indicate that the density of cavities is fluence dependent with homogeneous distribution of cavity sizes when fluences of 5×1016 and 1017 He/cm2 are used. The threshold fluence required to form cavities is found to be between 1 and 2×1016 He/cm2. For the 2×1016 He/cm2 dose, we observed loop punching induced by a concerted action of overpressurized bubbles, whereas He implants at doses of 5×1016 and 1×1017/cm2 lead to the formation of {311} defects. At the same time, non Rutherford elastic backscattering (NREBS) experiments using 2.5 MeV H+ provide the fraction of helium remaining in cavities after different annealing times at 800 °C. The NREBS data show a fast He release process for short annealing times (<2000 s). Then, the He amount decreases slowly and after 30 000 s about 40% of the helium still remain in cavities. Finally, an additional implantation with 50 keV He at 5×1016 He/cm2 shows the difference in cavity size distribution between MeV and keV implantation.

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A Monte Carlo simulation program was developed to calculate the variations of the channeled to random electronic stopping powers of He + in an energy 4 MeV in silicon single crystal along the major 100 , 110 and 111 axes. This paper discusses both simulation and experimental results that shed light on the contribution of these factors. Results obtained by our simulation are in good agreement with the experimental results.