It was noted that reduction of the background, using a coincidence-detection system in Doppler-broadening spectroscopic positron annihilation methods, permitted an examination to be made of the contribution that was made by high-momentum core electrons. This contribution was then used to identify chemical variations at defect sites. The technique was used to study various open-volume defects in Si, including the decorated vacancies that were associated with doping. In particular, a reduction in the degree of overlap of a localized positron and core-electron wave functions in the case of pure di-vacancies, was observed instead of the delocalized wave-functions of positrons in defect-free Si. Atoms of Sb, linked to vacancies, were shown to be the defects which were responsible for the saturation of electrical activity in Si that was highly doped with Sb.

S.Szpala, P.Asoka-Kumar, B.Nielsen, J.P.Peng, S.Hayakawa, K.G.Lynn, H.J.Gossmann: Physical Review B, 1996, 54[7], 4722-31