Interpretation of the modulus spectra of organic field-effect transistors with electrode overlap and peripheral regions: determination of the electronic properties of the gate insulator and organic semiconductor

The modulus spectra of organic field-effect transistors (OFETs) with electrode overlap and peripheral regions have been experimentally and theoretically investigated. The complex impedance of regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) OFETs with electrode overlap and peripheral regions was measured with a frequency response analyzer. The complex modulus was derived from an equivalent circuit of OFETs with overlap and peripheral regions using a four-terminal matrix approach. The modulus spectra of the P3HT OFETs were successfully fitted by those calculated using the expression derived from the equivalent circuit. Three structures were found in the modulus spectra of the P3HT OFETs owing to the dielectric properties of the gate insulator, transport properties of the organic semiconductor, and contact resistance from the low to high frequency ranges. The resistivity of the gate insulators and the field-effect mobility of working OFETs were determined using the values of the circuit components of the equivalent circuit obtained by fitting.