Extraction of band diagram parameters from Fowler-Nordheim model in silicon dioxide

In electric fields > 10(7) V/cm, we have observed that the conduction current through Si(n(+))/SiO2/poly-Si(n(+)) capacitors is larger than that predicted by the classical Fowler-Nordheim law for the case of a triangular potential barrier. This phenomenon appears for both gate polarities just before electric breakdown occurs. An attempt to model this excess current by direct tunneling or by other well-known conduction mechanisms such as Schottky, Poole-Frenkel or hopping effects has been unsuccessful. We have succeeded in interpreting experimental data by considering the SiO2 layer as a non-triangular potential barrier, which leads to a non-linear relationship between the tunneling length and the applied voltage. By using a semi-linear approach, an oxide conduction band model presenting two potential wells located at approximately from 2.5 nm to within +/- 0.2 nm from each oxide interface has been obtained. These two singularities may be related to the presence of a non-uniformly distributed positive charge in SiO2. (C) 2001 Elsevier Science B.V. All rights reserved.