Characterization of polymeric metal-insulator-semiconductor diodes

Metal-insulator-semiconductor (MIS) diodes are the two-terminal pendants of thin film transistors sharing the same basic layer structure. However, instead of the current-voltage characteristics one has to study the capacitance-frequency and capacitance-voltage behavior, which can give information about doping, mobile charges and trapping processes in these devices. We have investigated MIS structures based on poly(alkylthiophene) as semiconductor which were fabricated on glass substrates with polymeric insulator layers and compared their response to devices fabricated on Si/SiO2 substrates. From capacitance-voltage measurements the acceptor dopant concentration is determined for different preparation conditions. Typically these measurements show hysteresis between forward and reverse bias sweeps. We have investigated this behavior as a function of external parameters like sweep speed and temperature and discuss their possible origin. The analysis of the frequency response using appropriate equivalent circuits allows the extraction of material parameters, like conductivity and charge carrier mobility, which are compared to data obtained on thin film transistor structures. (C) 2004 Elsevier B.V. All rights reserved.