High-field capture of electrons by Coulomb-attractive centers in silicon dioxide

Electron capture by Coulomb-attractive oxide-charge centers in thin SiO2 films thermally grown on silicon was studied at room temperature and at 77°K for average oxide fields ranging from 5×105 to 3×106 V/cm. The observed capture cross section varied with the average oxide field, EOX, approximately as EOX-3. Such a strong field dependence cannot be accounted for by the Frenkel-Poole lowering of the potential % barrier alone which predicts an E OX-3/2 dependence. It is suggested that electron heating by the oxide field is likely at these high fields. Electron heating decreases the probability of capture. The observed field dependence can be explained by a combination of Frenkel-Poole and electron-heating effects. Although the zero-field capture cross section is expected to increase rapidly with decreasing lattice temperature, the observed high-field capture cross sections were about the same at room temperature and at 77°K. Such weak dependence of the high-field capture cross section on lattice temperature is consistent with Lax's model of cascade capture by acoustic-phonon emission.