Positron annihilation spectroscopy study of vacancy-type defects in He implanted polycrystalline α-SiC

Abstract The evolution of He implantation-induced defects in polycrystalline α-SiC has been investigated by a combination of positron annihilation Doppler broadening spectroscopy (DBS) and transmission electron microscopy (TEM). Samples implanted at room temperature with 230 keV He+ ions to fluences of 1 × 1015, 5 × 1015 and 1 × 1016 ions/cm2 were isochronally annealed in vacuum at temperatures up to 1400 °C with a step of 100 °C. Excellent correlation between the calculated damage profile and the positron annihilation depth profile were obtained at low annealing temperatures, after considering the positron depth distribution given by so-called Makhovian profiles. The DBS data from the peak region revealed a reasonable correlation between positron trapping at vacancy-type defects and the He-to-dpa ratio. Thermal annealing at 1400 °C resulted in the incomplete recovery of the microstructure, where large cavities distributed along grain boundaries in the damage peak region are surrounded by small agglomerations of (helium)vacancy-type defects.