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

Abstract

The energy gap of a carbon-contaminated 15 nm thick thermally grown SiO 2 film has been deduced from reflection electron energy loss spectroscopy (REELS) experiments using various primary electron energies (80 eV ≤ E p ≤ 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 ∼ 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 2 is clearly observed. The deduced energy gap is then 9.0 ± 0.1 eV ( E p ≥ 200 eV) as expected. These findings are consistent with an in-depth analysis of the electronic properties of the film under investigation.