Dark conduction through anthracene crystals

Abstract

Dark currents through anthracene crystals with silver paste electrodes were studied as functions of temperature, applied voltage, and time. Activation energies between 0.5 eV and 2.9 eV were measured, there being a definite correlation between log ¿0 and E (the compensation effect'). However, it was shown that the compensation effect arises from the calculation of ¿0 and E, and not from a true linear free-energy relationship. As simple carrier generation mechanisms were inadequate to explain the temperature-dependence results, a model involving transitions between two limiting mechanisms was invoked and developed. The voltage-dependence results are shown to arise by a transition from SCL currents at low voltages, to barrier-limited currents (BLC) at higher fields, where the Schottky effect controls the current-voltage response. Vindication of the choice of this model is obtained from the calculated values of the parameters ¿, the permittivity of anthracene; A, the Richardson constant; Ø, the surface energy barrier for hole injection from silver paste into anthracene; and WE(Ag), the work function for silver paste electrodes.