First-principles study of iron and iron pairs in Si

Iron is a common transition metal contaminant in Si. The isolated interstitial and several iron–acceptor pairs have been identified by DLTS, EPR, ENDOR and/or other techniques, then studied by theory. Iron also interacts with radiation and implantation damage. Much less is known about these interactions. In this contribution, we present preliminary results of ongoing calculations of interstitial iron, Fe pairs and their interactions with vacancies in Si. The calculations are done in periodic supercells. The electronic states are obtained from spin–density–functional theory with plane wave basis sets. The geometries are optimized using conjugate gradients. The binding energies, charge and spin states are calculated, and the electrically-active gap levels are estimated.