Hyperfine interactions of thePbcenter at theSiO2/Si(111) interface

Multiple-scattering Xα results are reported which show that spin polarization must be included to obtain a detailed understanding of the hyperfine spectra of the Si dangling-bond ${\mathrm{P}}_{\mathrm{b}}$ defect at the ${\mathrm{SiO}}_2$/Si(111) interface. The largest superhyperfine interaction is found to be produced not by the trivalent Si atom’s nearest neighbors as has been commonly assumed, but by three second-nearest neighbors located behind the defect in bulk c-Si. Our ${\mathrm{P}}_{\mathrm{b}}$ center results support the threefold-coordinated Si model for this defect; they also suggest a straightforward interpretation of recent ESR data on the dominant paramagnetic center in a-Si:H.