Energy gap-determination of a carbon contaminated thermal silicon oxide thin film using reflection electron energy loss spectroscopy

The energy gap of a carbon-contaminated 15 nm thick thermally grown SiO2 film has been deduced from reflection electron energy loss spectroscopy (REELS) experiments using various primary electron energies (80 eV less than or equal to E-p less than or equal to 1500 eV) and a standard single-pass cylindrical mirror analyzer (CMA). Doing so the probed depth is expected to increase with E-p. An adsorbed carbon concentration of similar to 18 at.%, as deduced from an Auger electron spectroscopy (AES) analysis, induces the appearance of wide peaks of localized gap states in the REELS spectrum recorded with E-p = 80 eV. The existence of an energy gap in the surface region of the sample is thus questionable. However, when E-p is increased to 200 eV the intensity of these gap states vanishes and the characteristic REELS spectrum of amorphous SiO, is clearly observed. The deduced energy gap is then 9.0 +/- 0.1 eV (E-p greater than or equal to 200 eV) as expected. These findings are consistent with an in-depth analysis of the electronic properties of the film under investigation. (C) 1997 Elsevier Science B.V.