Three-Carrier Theory of the High-Field Conductivity of Irradiated Non-Polar Liquids

As the voltage applied to an irradiated dielectric liquid is increased, the current increases also, but at less than a proportional rate, so that the slope of the current-voltage characteristic continually decreases. At a certain point, however, the curve becomes a straight line, and the current rises linearly with the voltage thereafter, until the breakdown region is reached. Similar behavior is observed in gases with the important difference that the slope of the characteristic in the linear region is zero. The behavior in gases is readily explained by a theory in which the observed characteristic arises as a result of the interaction of two charge-carrying species, positive and negative ions. Such an explanation cannot, however, be applied in the case of a liquid because of the non-zero slope of the linear portion of the characteristic. Several explanations have been offered in the literature, but none of these is completely satisfactory. In this paper a new three-carrier theory is suggested which takes account of the mobility, generation, and recombination of electrons as well as positive and negative ions. The theory can readily match experimental results and also appears to predict an additional rise in the current density as the electric field strength approaches breakdown values.