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

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Abstract
DC electrical measurements have been made for a wide lead phthalocyanine (PbPc) thickness range (d ~ 0.5–5.0 µm). 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 · 1–21) × 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 0.4–20 V 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.