Injection-Limited Currents in Insulators

Abstract

A general treatment of the injection-limited currents (ILC) at the insulator intersurface, based on the continuity equation including source current, is presented. Various approximations are discussed of which the one-dimensional Onsager model is a particular case for a weak gradient source current or the injection distance approaching zero. A coordinate-dependent geminate recombination is introduced into this model. Formal requirements leading to analytical, tractable solutions divide the electric field (F) range into two regimes: low-field regime (LFR) (F5.2 ε T ² V/m). At room temperature T=293 K and with typical dielectric permittivity ε=4, F _LFR 10⁶ V/m. In the approximations discussed the current-field dependence is linear or sublinear in the LFR and follows the function j ∞F ^3/4 exp (a F ^1/2) (a=constant) in the HFR. Comparison of the theory with the experimental data shows that the current changes at the predicted division value of the field and shows good agreement in the HFR. In the LFR, experimentally observed ILC follow the function j ∞exp (-b F ^-1/2) (b=constant). It is shown that it is caused by surface-trap limitation of the injection currents (STLIC).