A review was presented of the structural and hyperfine properties of Si dangling bond defects occurring in amorphous SiO2, and at various Si/SiO2 interfaces. These defects had in common a singly-occupied orbital on a trivalent Si center. A briefly summary was first given of the most important methodologies for calculating hyperfine parameters; pointing out their advantages and drawbacks. The properties of the defect centers composed of Si≡SinO3-n kernels, with n varying from 0 to 3, were then considered in a systematic manner. Three important factors were presented which affected the hybrid state of the unpaired dangling bond. These were the local geometry around the defect center, the electronegativity of the first-neighbor atoms and the polarization effect due to the oxide environment around the dangling bond. It was demonstrated that the cage polarization effect significantly increased the Fermi contact term of the defect Si atom, and the relevant implications were considered. Interactions between the dangling orbital and the O atoms belonging to the oxide cage were also quantified by focussing on the 17O hyperfine couplings. For various defects in amorphous SiO2 and at Si/SiO2 interfaces, assignments to Si≡SinO3-n structural units were considered in relation to available experimental data. In particular, the charge state of the Eγ' center, the peculiar hyperfine properties of the S center, and the atomic structures of the three Pb-type centers were addressed.

Modelling of Paramagnetic Trivalent Silicon Defect Centres in Amorphous Silica and at Si–SiO2 Interfaces. A.Stirling, A.Pasquarello: Journal of Physics - Condensed Matter, 2005, 17[21], S2099-113