SCLC measurements in nickel phthalocyanine thin films

Sandwich structures of Au/NiPc/Au were fabricated by sequential vacuum thermal sublimation onto borosilicate glass substrates. dc electrical measurements were performed for several NiPc thin films of different thickness in the range (d = 0.25-1.09 μm). The relative permittivity was measured at a low frequency of 100 Hz, yielding a value of εr = 2.74. This value is considerably lower in comparison with previously published data for various phthalocyanine materials. Current density-voltage characteristics at room temperature reveal an Ohmic conduction in the lower voltage range, followed by SCLC in the higher range, where the latter was found to be controlled by an exponential trap distribution. The plot of current density versus thickness provides further evidence of this effect. The results are analyzed in terms of exponential trap distribution yielding the following values: The temperature parameter characterizing the exponential trap distribution Tt = 1165 K, the concentration of thermally generated holes p0 = 1.40 × 1016 m-3, trap concentration per unit energy range P0 = 4.71 × 1043 J-1 m-3 and total concentration of traps Nt(e) = 7.57 × 1023 m