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 curre nt through Si(n(+))/SiO2/poly-Si(n(+)) capacitors is larger than that predi cted by the classical Fowler-Nordheim law for the case of a triangular pote ntial barrier. This phenomenon appears for both gate polarities just before electric breakdown occurs. An attempt to model this excess current by dire ct 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-tr iangular potential barrier, which leads to a non-linear relationship betwee n the tunneling length and the applied voltage. By using a semi-linear appr oach, an oxide conduction band model presenting two potential wells located at approximately from 2.5 nm to within +/- 0.2 nm from each oxide interfac e 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.