Electron-paramagnetic-resonance study of the microscopic structure of the Si(001)-SiO2interface

The defects of the Si(001)-${\mathrm{SiO}}_2$ interface have been studied by the electron-paramagnetic-resonance (EPR) technique taking advantage of the high specific surface area of porous silicon. This interface is characterized by the presence of two interface defects ${\mathit{P}}_{\mathit{b}0}$ and ${\mathit{P}}_{\mathit{b}1}$. We report here a detailed study of the ${\mathit{P}}_{\mathit{b}1}$ defect, which, in spite of being a dominant defect of this interface, had escaped any detailed EPR study up to now due to sensitivity limitations. The ${\mathit{P}}_{\mathit{b}1}$ defect is characterized by spin S=1/2, a monoclinic I point symmetry and principal values of the g tensor ${\mathit{g}}_1$=2.0058, ${\mathit{g}}_2$=2.0029, ${\mathit{g}}_3$=2.0069. Unlike the ${\mathit{P}}_{\mathit{b}}$ and ${\mathit{P}}_{\mathit{b}0}$ defects, its linewidth of 4.5 G is isotropic and frequency independent, indicating an atomic configuration not influenced by stress distributions. The central ${}_{}{}^{29}{}_{}{}^{}\mathrm{Si}$ hyperfine interaction of the ${\mathit{P}}_{\mathit{b}1}$ defect is at least a factor of 2 smaller than that of the ${\mathit{P}}_{\mathit{b}}$ and ${\mathit{P}}_{\mathit{b}0}$ defects, implying a delocalization of its electron wave function over more than one Si nucleus. The properties of the ${\mathit{P}}_{\mathit{b}1}$ defect are compatible with a dangling-bond defect on a Si dimer as previously proposed by Edwards.