Structure and Hyperfine Interaction of Si3≡ Si• Defect Clusters

The Pb center located at the Si(111)/SiO2 interface1,2 and the D-center in a-Si and a-Si:H3–5 each have g-tensors whose isotropic part g ~ 2.0055. A value of g = 2.0055 ± 0.0005 is considered to be diagnostic of radicals with the schematic structure Si3 ≡ Si•, in which the trivalent defect atom is bonded into the bulk material through three Si nearest neighbors. When the nearest neighbors are not all Si atoms (e.g., the E′ center in silica, O3≡ Si•) characteristically different ESR signatures are obtained. The similarity of the Pb and D-center g-factors suggests that the two defects might resemble each other closely not only in their schematic structures, but also in their detailed physical conformation and electronic structure.