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The effect of electron traps on the current-voltage (J-V) relationship and the charge distribution in insulators, under conditions of space-charge-limited current flow, is well understood. This paper extends the consideration of trapping effects into the region of emission-limited current flow. Trapped space charge distorts the field in the insulator so that the usual J-V relationship for emission-limited current in a vacuum, J ∝ exp (constant) V½, which is often applied to insulators, will not be observed initially. It is shown that at sufficiently high voltages, however, the trapped space charge becomes negligible and the above J-V relationship is obtained. A calculation is done to obtain the J-V characteristic in an insulator throughout the emission-limited region, for typical values of trapping depth, trapping density, and barrier height. The resulting curves show that the transition from space-charge-limited to emission-limited current occurs at reasonable voltages, and that at these voltages, space-charge effects are large enough to be readily observed in practice. It is shown that the absence of space-charge effects at higher voltages is a consequence of field lowering of the barriers around trapping sites. In addition, several general results are obtained concerning field and charge distributions in insulators containing traps.
Frank et al. (1967) studied this question.