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

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Abstract
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 EOX −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.