Transport properties in lead phthalocyanine thin films for use in FET structures

DC electrical measurements have been made for a wide lead phthalocyanine (PbPc) thickness range (d ˜ 0·5-5·0µm). Measurements of capacitance as a function of inverse thickness revealed a low frequency relative permittivity (∈r ˜ 3·9), slightly higher than in copper phthalocyanine. At low voltages Ohm's law was followed, with a thermally-activated hole concentration of (1·1-2·1)×1016 m-3. Above a threshold voltage Vt, a power-law dependence of current density on applied voltage was observed, indicating space-charge-limited conductivity, Vt varied in the range 0·4-20V and was approximately proportional to d2, providing further evidence for this effect. The results were accounted for in terms of an exponential distribution of traps of total concentration 2.8×1025 m-3 within the bandgap, as observed in similar organic materials. © 1990 Taylor & Francis Ltd.