Electron spin resonance was used to study neutron-induced defects in Si as functions of the annealing temperature, Ta. For Ta below 200C, the electron spin resonance response was dominated by the Si-P3 and Si-P6 spectra, as observed before. At Ta = 200C, a low symmetry center Si-H8, only once reported before, appeared. Here, a hyperfine doublet, corresponding to interaction with one 29Si nucleus, was resolved. In the Ta range above 250C, two other paramagnetic defects predominated. The first was the tetragonal center Si-B3: Mapping of the full angular dependence of known and newly-resolved 29Si hyperfine structure permitted conclusive identification of the tetra-interstitial (I4) in the positive charged state, based upon compliance of the data with previous theoretical calculations. Secondly, the observation of an unidentified trigonal center, Si-B5, was reported; exhibiting 2 hyperfine doublets corresponding to hyperfine interactions with 4 and 6 equivalent Si sites. The tri-interstitial I3 was proposed to be a provisional defect model. The annealing behavior and symmetry of these defects provided evidence for linking these paramagnetic B3 and B5 centers to the X and W optical centers, respectively.

Electron Spin Resonance Study of Paramagnetic Centers in Neutron-Irradiated Heat-Treated Silicon. D.Pierreux, A.Stesmans: Physical Review B, 2005, 71[11], 115204 (8pp)