1 1 A pr 2 00 0 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 (CP's) 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 Second-harmonic generation (SHG) is inherently sensitive to surface and interface properties of centrosymmetric materials. Recently, the spectroscopy of the second-harmonic (SH) intensity has been proved as a promising probe of surfaces and interfacial layers 1 and intensively employed in numerous works for oxidized 2 , reconstructed 3 and H-terminated 4 silicon surfaces. The resonances of the SH intensity are attributed in these cases to direct interband electron transitions. By analogy with the spectrum of the linear dielectric function ε(ω) the spectrum of the quadratic susceptibility χ (2) (2ω) of such semiconductor surfaces could be expressed as the superposition of several van Hove singularities (critical points (CP's) of the combined density of states) χ (2)