Direct observation of valence and conduction states near the SiO ₂/Si(100) interface

Valence and conduction states near the SiO₂/Si(100) interface were directly observed using soft x-ray absorption and emission spectroscopy. For the O K-edge absorption spectra, the step-like structures were observed at 531, 533 and 534.5 eV. These step-like structures observed at 531, 533 and 534.5 eV were assigned to an oxygen atom bonding to Si¹⁺ , Si ²⁺, and Si³⁺ of the interface, respectively. In the case of O K-edge emission spectra, with decreasing incident photon energy from 535 to 531 eV so as to shift the conduction band minimum of the interface towards Fermi energy, the corresponding valence band maximum was shifted to Fermi energy direction. Thus, the local band gap became narrower with the decrease of the oxidation number of the suboxide species. Further the interface structure was also discussed from the spectrum features.