Mossbauer study of the proximity gettering of cobalt atoms to He-induced nanosized voids in c-Si

We observe a strong gettering of ion implanted Co-57 to the internal surface of empty nanosized voids in c-Si, hampering normal silicide formation. The cavities are introduced by implanting He far above the solubility limits and subsequent desorption at 700 degrees C during 30 min. After Co-57 implantation and thermal treatment, a previously unobserved Mossbauer spectrum was recorded that could be fitted consistently with two quadrupole doublers. They differ largely in binding strength and electric-field gradient V-zz and we preliminarily interpret them as an edge site (strong binding, smaller V-zz) and a surface site (loose binding, larger V-zz) at the internal surface of the faceted voids. The spectra are stable upon high-temperature annealing.