Influence of lateral currents on capacitance spectra of organic metal-insulator-semiconductor structures with a ferroelectric insulator

The capacitance spectra of a metal-insulator-semiconductor (MIS) structure are discussed in terms of parasitic effects, caused by lateral currents along the insulator/ semiconductor interface. The organic materials Poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) and poly(3-hexylthiophene) (P3HT) were used for insulator and semiconductor, respectively. Capacitance-frequency (C-f) measurements are compared to numerically obtained spectra based on an equivalent circuit. Furthermore, capacitance spectra of a semiconductor-metal-insulator-metal (SMIM) structure were measured in order to identify the origin of the low frequency relaxation, found in the MIS C-f measurements. The studies suggested an increase of the capacitance by 10% at 0.01 Hz due to lateral currents. It was concluded that for probing frequencies > 1 Hz, parasitic effects on the capacitance spectra could be neglected. When the device was biased into accumulation prior to the measurement, the ferroelectric nature of the insulator led to an increase in the lateral spreading of charges.