Effects of FeCl3 as Oxidizing Agent on the Conduction Mechanisms in Polypyrrole (PPy)/pc-ZnO Hybrid Heterojunctions Grown by Oxidative Chemical Vapor Deposition

P-type polypyrrole (PPy) films are deposited on glass and on n-type polycrystalline ZnO (pc-ZnO) substrates by oxidative chemical vapor deposition under three different amounts of FeCl3 used as oxidizing agents to form hybrid heterojunctions. Their microstructure, morphology, and electrical characteristics are studied. Particularly, current-voltage characteristics of the PPy/pc-ZnO heterojunctions are analyzed by defining an electrical equivalent circuit. The extracted parameters, together with the estimated heterojunction barrier height and the HOMO energy level of the PPy, indicate that a thermionic emission of holes at the heterojunction determines the saturation current of the diode at low voltage. For larger FeCl3 amounts, the diode ideality factor increases indicating an increment of recombination by tunneling of charge carriers occurring at the heterojunction. This is attributed to a narrowing of the space charge region due to an increment of the number of charge carriers with a growing amount of FeCl3. At high voltages, the PPy thickness influences the ohmic and spacecharge limited current mechanisms at the bulk region. (C) 2016 Wiley Periodicals, Inc.