Latent iron in silicon

It is usually assumed that the iron in iron-contaminated, boron-doped silic on exists as FeB pairs. The iron can be cycled between its interstitial (Fe -i) and paired (FeB) states with the total density Fe-i + FeB remaining con stant. We have discovered that iron can also exist in other paired states, which we believe to be Fe-vacancy or Fe-implant damage pairs. When these pa irs are destroyed and subsequently when FeB pairs form, we have observed an increased density. We refer to the excess iron (Delta FeB) after re-format ion as "latent" iron.