  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.
