New (S=1) EPR AA17 center in silicon — microplatelets or precursor of platelets?

New (S=1) EPR spectrum (labeled Si-AA17) is observed in irradiated high-purity hydrogen-contained silicon after annealing at ≥200°C. The AA17 defect has D3d symmetry with g∣∣=2.0028, g⊥=2.0106; A∣∣(29Si)=175.0 MHz, A⊥=89.0 MHz; and D∣∣=±33.6 MHz, D⊥=±16.8 MHz. It is paramagnetic in a neutral charge state. An analysis of 29Si hf interaction has shown that 62% of the resonant wave function belong to two equivalent silicon atoms. The magnitude of zero-field splitting (D=16.8 MHz) of AA17 has a smallest value among the known (S=1) EPR centers in silicon and indicates that the distance between two equivalent Si sites (spins) creating the S=1 state, is ∼12 Å along to 〈111〉 axis. Most suitable model of the defect is the {111} planar hexavacancy situated between two 〈111〉 dangling Si bonds separated by ∼12 Å. Each of these dangling bonds is formed as a result of saturation of the nearest Si atom by one hydrogen located at AB position.