Second-harmonic interferometric spectroscopy of the buried Si(111)-SiO$_2$ interface

The second-harmonic interferometric spectroscopy (SHIS) which combines both amplitude (intensity) and phase spectra of the second-harmonic (SH) radiation is proposed as a new spectroscopic technique being sensitive to the type of critical points (CPs) of combined density of states at semiconductor surfaces. The increased sensitivity of SHIS technique is demonstrated for the buried Si(111)-SiO$_2$ interface for SH photon energies from 3.6 eV to 5 eV and allows to separate the resonant contributions from $E^prime_0/E_1$, $E_2$ and $E^prime_1$ CPs of silicon.