Optical second-harmonic phase spectroscopy of Si(111)-SiO/sub 2/ interface

Summary form only given. We report on the observation of the spectral dependence of the phase of second harmonic (SH) waves generated from Si(111)-SiO/sub 2/ interface with SH photon energies from 3.6 eV to 5 eV. We directly observe that the real part of silicon quadratic susceptibility, contrary to linear susceptibility, does not change the sign while passing through E/sub 2/ resonance. We interpret such a spectral behavior as indicating the strong influence of interband transitions located near E/sub 1/' critical point.