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The theoretical shape of the potential barrier for a dielectric film interposed between two metals is discussed, with particular emphasis on the effects arising from ionic defects, interfacial dipoles, and field penetration of the electrodes. It is shown that both ions and the extension of their electric fields penetrating the electrodes have a significant effect on barrier shape. By applying Stratton's theory of tunneling, an analytic expression is obtained for the increase of tunnel current due to ion penetration of the barrier. For ion concentrations of the order of one per unit area equal to the film thickness square, the tunnel current increases by an order of magnitude. Numerical results are also presented for an Al–Al2O3–Al barrier, where the analytic solution is only marginally valid.

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It is shown that measurement of thermal activation energies for both Ohmic and space-charge-limited conduction over a broad temperature range enables the deduction of both depth and concentration of localized levels in a semi-insulator, while measurement of the activation energy for Ohmic conduction alone is rarely definitive for a wide band-gap material. The basis for interpreting thermal activation energies for electrical conduction is discussed in detail. The analysis is applied to recent results on HgS, GaP, CdS, andZnS:Cd.

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