Space-Charge Effects on Emission-Limited Current Flow in Insulators

Abstract

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.

Magnetic field effects on emission and current in Alq3-based electroluminescent diodes

“…3). The voltage increase in Dj=jð0Þ can be explained by space-charge effects on the electron emission current from the cathode [15]. The presence of the space-charge reduces the MFE on the current because the number of carriers supplying the current is only partly controlled by the direct injection from the electrode contact.…”

Composite polypyrrole-containing particles and electrical properties of thin films prepared therefrom

“…When the voltage applied to the electrodes increases, x m moves towards the injecting electrode and f m decreases [46,47]. As the voltage increases further, the barrier height can no longer be lowered by the removal of opposite charge from the injecting electrode and the barrier lowering takes place by the interaction of the image force with the applied field (Schottky effect, [48]).…”

“…The current becomes contact-or emission-limited (ELC) rather than bulk limited. However, due to a large number of traps present in the insulator, the space charge still exists; its influence on the ELC j-U characteristic was considered by Frank and Simmons [46]. They also assumed that traps modify, depending on the electric field, the ratio of free and trapped charge densities.…”

Space‐Charge‐Limited Currents at High Electric Fields

“…Version of (5) were obtained by Frank and Simmons [5] and Arnett [7]. Evaluating (5) at x = L, where L is the insulator thickness, we obtain an expression for the current in terms of the contact-field values,…”