Electronic structure of SiO2, SixGe1-xO2, and GeO2 from photoemission spectroscopy

Abstract

The valence-band structure of the mixed silicate SixGe1-xO2 was investigated for a range of compositions by x-ray and uv photoemission spectroscopy. Structure in the valence band, which is derived from the oxygen nonbonding orbitals and from the Si-O bonding orbital, is seen to move continuously in initial energy in going from SiO2 to GeO2. The width of the nonbonding bands at the top of the valence band decreases from about 3.3 eV in SiO2 to 2.0 eV in GeO2 in which separate peaks are no longer resolved. The decrease in width of the nonbonding bands is correlated with an increase in the average oxygen-oxygen separation from 2.62 to 2.85. The results indicate that the width of the nonbonding bands is largely due to oxygen wave-function overlap. The valence bands measured by photoemission from the mixed oxide are not a superposition of SiO2 and GeO2 valence bands. On the other hand, band-gap excitations, as determined by energy-loss satellites on the photoemission spectra, were found to be a superposition of those for SiO2 and GeO2, indicating local conduction-band states centered about the Ge and Si sites. © 1977 The American Physical Society.