Ohmic and space-charge limited conduction in cobalt phthalocyanine thin films

Current density-voltage characteristics have been obtained from thin films of cobalt phthalocyanine when sandwiched between ohmic gold contacts. Results showed ohmic conduction in the Tower voltage range and space-charge limited conduction controlled by an exponential distribution of traps above the valance band edge for a higher voltage section. Analyses of the results yielded the following values: the hole mobility mu approximate to 4.4 X 10(-6) m(2) V-1 S-1, the room temperature hole concentration p approximate to 2.9 X 10(14) m(-3), concentration of traps per unit energy range at the valence band edge P approximate to 1.3 X 10(43) J(-1) m(-3), the temperature parameter T-t of trapping distribution 1288 K, and the total trapping concentration N-t approximate to 2.3 x 10(13) m(-3). The dependence of capacitance C on temperature shows that C is temperature insensitive, below 300 K, above which there is a rapid increase with increasing temperature and finally at about 400 K, C saturates. Such characteristics were found to be in good qualitative agreement with the existing equivalent circuit models assuming ohmic contacts. (C) 1997 Elsevier Science S.A.