The effect of charged centers in thermally stimulated currents: Application to poly(N-vinylcarbazole)

In measuring the field dependence of DC conductivity in amorphous dielectrics one often finds, that the logarithm of current plotted vs. square root of electric field yields a straight line. This effect may be due to decrease of occupation probability of a trap, charged when empty, under the influence of the external field. Frenkel and Poole (1) discussed this phenomenon in terms of the Coulomb interactions with the charged center. The electrode injection (Schottky effect (2)) can, however, yield the same type of field dependence, and it is often very difficult to distinguish both phenomena. More recently, the same type of field dependence was found in the time-of-flight measurements of mobility. This effect is now seen to be so widespread that doubts have been raised whether the presence of charged traps in amorphous dielectrics solely accounts for the observed field dependence of various electrical properties in these materials.