Vacancy engineering by He induced nanovoids in crystalline Si

Positron annihilation spectroscopy (PAS) in the Doppler broadening mode is used to study the effects of He and B implantation, and subsequent annealing on the vacancy profile of crystalline Si. The existence of two void layers, one consisting of large voids at the projected range (R(p)) of He and another containing 'nanovoids' slightly larger than divacancies at roughly halfway between R(p) of He and the surface is shown for samples implanted with He. Furthermore, the same nanovoid layer is shown to be absent from samples co-implanted with B, implying that interstitials created during B implantation get trapped in the nanovoids and fill them, thus indicating that the nanovoid layer is behind the hindrance of B diffusion