ELECTRON-PARAMAGNETIC-RESONANCE STUDY OF THE MICROSCOPIC STRUCTURE OF THE SI(001)-SIO2 INTERFACE

The defects of the Si(001)-SiO2 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 P-b0 and P-b1. We report here a detailed study of the P-b1 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 P-b1 defect is characterized by spin S = 1/2, a monoclinic I point symmetry and principal values of the g tensor g(1) = 2.0058, g(2) = 2.0029, g(3) = 2.0069. Unlike the P-b and P-b0 defects, its linewidth of 4.5 G is isotropic and frequency independent, indicating an atomic configuration not influenced by stress distributions. The central Si-29 hyperfine interaction of the P-b1 defect is at least a factor of 2 smaller than that of the P-b and P-b0 defects, implying a delocalization of its electron wave function over more than one Si nucleus. The properties of the P-b1 defect are compatible with a dangling-bond defect on a Si dimer as previously proposed by Edwards.