Identification of strained silicon layers at Si-SiO2interfaces and clean Si surfaces by nonlinear optical spectroscopy

Abstract
Optical second-harmonic and sum-frequency spectra of clean and oxidized Si(100) and Si(111) samples reveal a strong resonance band at 3.3 eV photon energy. It is concluded that the resonance arises from direct transitions between valence and conduction band states in a few monolayers of strained silicon at the Si-SiO2 interface and at the selvedge of clean reconstructed silicon surfaces.