Electron spin resonance study of the Si-B5 paramagnetic center in neutron-irradiated heat-treated silicon

A detailed electron spin resonance study has been performed on the Si-B5 paramagnetic defect (C3v symmetry) in neutron-irradiated c-Si subjected to annealing in the range 200–350 °C. A rich and detailed 29Si hyperfine structure is newly resolved and fully angularly mapped. Computer simulations point toward the defectʹs unpaired electron as having its strongest interaction with one Si site, followed by interaction with two shells of two equivalent Si sites each, and two more shells of both three equivalent Si sites. Two previously proposed tri-interstitial models are discussed as possible candidates for the Si-B5. However in lack of extensive theoretical calculations, assignment of the Si-B5 to one of the tri-interstitial models remains undecided. In addition we also report on an unusual temperature behavior of the hf splittings as well as the principal g matrix values.