Abstract
This paper introduces present state of our novel attempt to apply organic field-effect transistors (OFETs) to large-area flexible terahertz-wave (THz-wave) sensors utilizing small band-edge fluctuation in organic semiconductors. We found that small random potential fluctuation always appears at the highest-occupied-molecular-orbital (HOMO) band edge of pentacene thin films and its amplitude is insensitive to the growth conditions of the pentacene layer and the composition of the substrate. The height of potential barriers in the fluctuated band is within the range of 1-10 meV, which corresponds to the THz photon energy. According to the modulation-absorption spectroscopy with OFET structure, holes in pentacene exhibited sufficiently large absorption cross-section in THz range. The Drude-Lorentz model cannot explain the shape of absorption spectra of the holes accumulated in pentacene. THz-wave electric-field distribution in OFETs was also calculated using the finite-difference time-domain (FDTD) method to obtain the dependence of sensitivity on frequency and polarization direction.
