We have investigated the strongest infrared absorption mode in silicon oxide films obtained at low temperatures (anodic and plasma oxides). The asymmetric stretching transverse mode of the Si-${\mathrm{O}}_4$ tetrahedra, centered at 1070 ${\mathrm{cm}}^{\mathrm{-}1}$, exhibits an interesting multiple-resonance structure on the high-energy side of the infrared spectrum. A transverse-optical (TO) mode at 1200 ${\mathrm{cm}}^{\mathrm{-}1}$ and a longitudinal-optical (LO) mode at 1150 ${\mathrm{cm}}^{\mathrm{-}1}$, both modes associated with a LO-TO frequency splitting, and another longitudinal-optical mode at 1250 ${\mathrm{cm}}^{\mathrm{-}1}$, associated also with a LO-TO splitting of the 1250- and 1070-${\mathrm{cm}}^{\mathrm{-}1}$ peaks are also observed. An important increase in the intensity of the multiple-resonance feature, attributed to the water concentration present during the oxidation process, is observed. This effect is related to the increase in the short-range disorder in silicon oxide films attributed to OH and ${\mathrm{H}}_2$O incorporation during growth. In addition, x-ray-photoelectron-spectroscopy measurements reflect the influence of this short-range disorder on the O 1s and Si 2p core-level and valence-band spectra.

• Received 26 April 1994

DOI:https://doi.org/10.1103/PhysRevB.50.4881