  Recent experiments have demonstrated that the performances of organic FETs
strongly depend on the dielectric properties of the gate insulator. In
particular, it has been shown that the temperature dependence of the mobility
evolves from a metallic-like to an insulating behavior upon increasing the
dielectric constant of the gate material. This phenomenon can be explained in
terms of the formation of small polarons, due to the polar interaction of the
charge carriers with the phonons at the organic/dielectric interface. Building
on this model, the possible consequences of the Coulomb repulsion between the
carriers at high concentrations are analyzed.
