Effect of Schottky barrier on alternating current response of lead phthalocyanine

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Abstract
Measurements were made of the capacitance (1 kHz) and the dc conductivity of degassed, oxygen‐doped, and iodine‐doped single crystals of lead phthalocyanine (PbPc) as a function of temperature between room temperature and 250 °C. As the temperature was increased, the capacitance initially remained constant as expected, followed by an exponential increase similar to that of the conductivity and then saturated with an extraordinarily large value. Frequency dependence below 1 MHz of the capacitance and the loss tangent of PbPc film with aluminium electrodes was also measured at degassed and oxygen‐doped states. An apparent Debye‐type dispersion was observed. All the results obtained are consistently understood in terms of the Schottky barrier capacitance associated with the PbPc‐electrode contact. The oxygen doping exhibited remarkable influence on the alternating current response and this effect is considered to be due to changes in the barrier capacitance and the dc conductivity with doping.