Origin of the n-type field effect in polyaniline and oligoaniline thin films

We analyse the n-type field effect recently reported for protonated, layer-by-layer self-assembled polyaniline and oligoaniline thin films. An agreement is obtained between the experiments and a model, valid for three-dimensional variable-range hopping in a parabolic Coulomb gap. The results suggest that the wave-function decay length ξ and/or the dielectric constant ε vary with the position of the Fermi level (EF), with a positive derivative dln[ξ(EF)ε(EF)]/dEF in the order of a few eV−1. The apparent discrepancy between the p-type doping and n-type field effect is explained by the electron-hole asymmetry characteristic for aniline derivatives.