Low frequency capacitance characterization of α-phase nickel phthalocyanine/lead interfaces:: effects of temperature and oxygen doping

The Schottky barrier characteristics of evaporated alpha-phase nickel phthalocyanine/lead (alpha-NiPc/Pb) structures were investigated using the small AC signal capacitance-voltage (C-V) technique. It was established that for junctions fabricated and tested in situ at room temperature detection of the barrier depletion layer is not possible. Voltage-dependent capacitance characteristics are detected only upon heating or after exposure of the devices to dry air for prolonged periods of time. The C-V response is attributed to the increase of carrier concentration, first due to increased temperature and second due to p-type doping induced by oxygen absorption within the alpha-NiPc layer. The acceptor state density was determined to be in the range 1.10 x 10(22) to 7.15 x 10(22) m(-3) for devices tested in situ and after exposure to dry air for 120 h, respectively. (C) 2004 Elsevier Ltd. All rights reserved.