It was noted that a new electron paramagnetic resonance spectrum formed during annealing at above 200C in irradiated high-purity H-containing material. It was stable at up to 450C. The defect had D3d symmetry, an electronic spin of S = 1 and was paramagnetic in a neutral charge state. An analysis of 29Si hyperfine interactions showed that 62% of the resonant wave function belonged to 2 equivalent Si atoms. The magnitude (16.8MHz) of the zero-field splitting indicated that the distance between the 2 equivalent Si sites which created the S = 1 state was about 1.2nm; along the {111} axis. Piezospectroscopic measurements showed that vacancy-like defects should be sited between equivalent Si atoms. The proposed model for the defect was that of a {111} planar hexavacancy which was centered between two <111> dangling Si bonds that were separated by 1.2nm; with each dangling bond being formed as a result of saturation of the nearest Si atom by one H atom.

Hydrogen-Induced Extended Complexes in Silicon Y.V.Gorelkinskii, K.A.Abdullin, B.N.Mukashev: Physica B, 1999, 273-274, 171-5