AC ELECTRICAL-PROPERTIES OF THERMALLY EVAPORATED THIN-FILMS OF COPPER PHTHALOCYANINE

The a.c. electrical properties of copper phthalocyanine (CuPc) thin films have been studied in the frequency range 10(2)-2 x 10(4) Hz and in the temperature range 173-360 K. The a.c. conductivity sigma(omega) was found to vary as omega(s) with the index s less-than-or-equal-to 1, indicating a dominant hopping process at low temperatures and high frequencies. At higher temperatures and lower frequencies, free carrier conduction with mean activation energy of 0.3 eV was observed. Capacitance and loss tangent decreased with frequency and increased with temperature. Such characteristics were found to be in good qualitative agreement with the existing model of Goswami and Goswami. Both the conductance and capacitance were lowered over the entire frequency spectrum after heat treatment at 370 K. This reduction was ascribed to the desorption of oxygen by the heat treatment, as previously observed in d.c. conduction measurements.