Characterization of recombination centers in Si epilayers after He implantation by direct measurement of local lifetime distribution with the ac profiling technique

The distribution of recombination centers induced in Si epi-substrates by helium (He) implantation is obtained for the first time by direct measurement of local recombination lifetime profile along the layer, using the ac differential lifetime profiling technique. The different energy levels of the recombination centers induced by He implantation at different doses and energies have been extracted, as a function of the position in the layer, by temperature scanning of the lifetime profiles. The lifetime measurements clearly demonstrate the presence of a secondary defect distribution that extend from the region of maximum primary damage both at lower and higher depths respect to the stopping range depth, due to the relatively large concentration of primary defects created near the stopping range, and give a coherent picture of the effects of He implant on the “local” lifetime.