Junction Properties of Nickel Phthalocyanine Thin Sandwich Film Structures Using Dissimilar Electrodes

Multilayer sandwich structures of Au/NiPc/Pb were fabricated in-situ utilising a sequential deposition technique. Electrical measurements were performed on both in-situ and oxygen-doped samples. Under forward bias conditions, at low voltages, Ohmic conduction, and at higher voltages SCLC were identified. However, in the reverse bias, a transition from electrode limited to bulk limited conduction process was evident. Depletion region width as well as the potential barrier height (φb) at the NiPc/Pb interface were calculated from the reverse J-V characteristics yielding values of 183 nm and 1.03 eV, respectively. After exposure to dry air a strong rectifying effect was observed. The latter is suggested to be associated with the change in the work function of NiPc as a result of oxygen adsorption. The potential barrier height for oxygen-doped samples was calculated yielding a value in the range of 0.955-0.96 eV. Hole and trap parameters, for both in-situ and oxygen-doped sample devices were also evaluated. Derived values suggested that trap concentration associated with higher voltage characteristic is significantly higher for the oxygen-doped sample. This type of behaviour is strongly believed to be due to an oxidisation process occurring near the NiPc/Pb interface.