An investigation was made of Fe by electron paramagnetic resonance and photo-electron paramagnetic resonance in initially B doped Si samples in which the Fe concentration exceeded the B content. A new electron paramagnetic resonance spectrum, showing orthorhombic-I symmetry was observed and could be fitted by an effective spin Hamiltonian with the parameters S = 3/2, g = 2.07, and E/D = 0.68. This spectrum was identified as being a new modification of a Fe2B center which had the same symmetry, but a different configuration of the constituent atoms. It was also possible to determine the donor level of the old Fe2B center as being Ev+0.57eV. An investigation was also made of the Fe2 donor. According to this interpretation, the energy levels of the transitions from Fe2+ to Fe20 and from Fe20 to Fe2+ were determined to be Ev+0.61eV and Ec-0.67eV, respectively. This suggested an unusual lattice relaxation upon electron capture.

Electron Paramagnetic Resonance and Photo-Electron Paramagnetic Resonance Studies of Aggregate Centers with Two Iron Atoms in Silicon. S.Strube, H.Vollmer, R.Labusch: Applied Physics A, 2005, 81[1], 87-91