Field effect in organic devices with solution-doped arylamino-poly-(phenylene-vinylene)

MOS capacitors and field effect transistors with arylamino-PPV as an active layer have been prepared and characterized. For this material we developed a doping method to increase the conductivity. The field effect has been de monstrated by the measurement of capacitance voltage (CV)-curves of the MOS capacitor. In accumulation the oxide capacitance is only achieved for low frequencies. At positive gate voltages inversion has not been observed. The p-doping concentrations are in the range of 10(16),..., 10(18) cm(-3). Wit h the realized thin film transistor structure a typical transistor behaviou r has been demonstrated. The estimated value for the mobility is in the ord er of 10(-4) cm(2)/Vs. This low value causes a high relaxation time. The me asured characteristics of both devices show a large hysteresis for differen t sweep directions and a shift of the curves for repeated measurements. Mob ile ions, the kinetics of incomplete ionization, chemical reactions of iodi ne or the polaron-bipolaron conversion might influence this behaviour. Cond itions to achieve inversion were determined by two-dimensional (2-D) simula tion of both devices. It turns out that, due to the low intrinsic density o f organic materials, one cannot demonstrate an inversion layer in an MOS ca pacitor. But in the transistor structure the minority carriers are injected from source and drain into the channel generating an inversion layer. Furt her experimental investigations are necessary to prove this prediction and to clarify the hysteresis effect. (C) 2000 Elsevier Science Ltd. All rights reserved.