Electrical Conductivity of Potassium Films on Potassium Chloride

Potassium was evaporated onto a KCl crystal at 77°K under a vacuum of 10—9 Torr. Conductivity measurements were made before and after the film was annealed at room temperature. For the stable film, Ohm's law is obeyed up to about 25 V/cm and the temperature dependence of the conductance follows G=G0exp(—ΦE/kT) with ΦE=0.05–0.063 eV. The preannealed film became very unstable in a field near 250 V/cm and the current—voltage relation is nonlinear. The experimental results strongly suggest that in the stable film, the conduction is by the mechanism of impurity conduction subject to the Schottky effect while in the unsettled film, the currents, though mainly carried by electrons, are decisively controlled by mobile ions.