Dielectric Properties of Some Powdered Organic Semiconductors

Abstract

The use of electrical conductivity measurements to characterize the charge density and/or mobility parameters of a material is discussed. The common practice of using simple, pressed electrodes with dc measurements is felt to be grossly inferior to four‐probe techniques. Even this refinement, however, is subject to considerable error for powdered samples. Many workers have used fairly simple ac techniques to eliminate interparticle contact resistances in organic semiconductors; this approach is shown to have been misapplied. It is possible, however, to measure what appears to be a specific conductivity (independent of packing pressure or filling factor) by more elaborate ac analysis. Measurements of the effective parallel resistance and capacitance are given for anthracene (powder and single‐crystal), metal‐free β‐phthalocyanine, and a β‐carotene tri‐iodide complex for a frequency range of 0.05 cps to 300 Mc/sec.