Transmission, photoconductivity, and the experimental band gap of thermally grown SiO2films

Abstract

Optical transmission and photoconductivity spectra (7-14 eV) and the field dependence of photoconductivity are presented for thermally grown (amorphous) Si${\mathrm{O}}_{2}$ films. It is argued that the clearest experimental determination of the band gap in Si${\mathrm{O}}_{2}$ can be obtained from the field dependence of photoconductivity and its similarity to internal photoemission; a band gap of 9.3 eV for amorphous Si${\mathrm{O}}_{2}$ is deduced from the data. In view of this result some recent experimental band-gap determinations are criticized and the literature on this subject is examined. The transmission experiments were performed on thin thermally grown (amorphous) Si${\mathrm{O}}_{2}$ films (450-5000 \AA{}) produced by etching off the silicon substrate and using a fabrication method which is described in detail. The photoconductivity measurements were performed on Al-Si${\mathrm{O}}_{2}$-Si structures (Si${\mathrm{O}}_{2}$: 600-3500 \AA{}). Diode experiments for detecting photoluminescence and possibly excitons are also described. The upper limit on photoluminescence yield was determined as \ensuremath{\sim}${10}^{\ensuremath{-}4}$.