Lattice location of implanted Co in heavily doped $n^+$- and $p^+$-type silicon

Abstract

We have studied the influence of electronic doping on the preferred lattice sites of implanted ${^{61}\text{Co}}$, and the related stabilities against thermal annealing, in silicon. Using the $\beta ^-$ emission channeling technique we have identified Co on ideal substitutional (ideal S) sites, sites displaced from bond-centered towards substitutional (near-BC) sites and sites displaced from tetrahedral interstitial towards anti-bonding (near-T) sites. We show clearly that the fractions of Co on these lattice sites change with doping. While near-BC sites prevail in $n^+$-type Si, near-T sites are preferred in $p^+$-type Si. Less than $\sim$35% of Co occupies ideal S sites in both types of heavily doped silicon, showing that the majority of implanted Co forms complex defect structures. Implantation-induced defects seem to getter more efficiently Co in lightly doped n-type than in heavily doped $n^+$- or $p^+$-type silicon. The formation of CoB pairs in $p^+$-type silicon and its possible influence on the lattice sites is discussed.