Vacancies and vacancy defects in Si observed by positron annihilation

Diffusion of atoms at lattice sites is mediated via vacancies or interstitials. This paper briefly reviews what has been learned on vacancy defects in Si using the positron annihilation spectroscopy. Both isolated vacancies, vacancy-donor and vacancy-oxygen (A center) pairs as well as divacancies have been identified after electron irradiation. Positron lifetime values give information on the charge states and open-volume relaxations of the vacancy defects. No reliable observation of vacancies at thermal equilibrium exists indicating very low (< 0.5 ppm) vacancy concentrations at high temperatures. In highly n-doped Si, vacancy-donor (P, As, Sb) pairs or complexes have been detected as native defects. The role of divacancies as recombination centers in H+ implanted Si is discussed.