ORIGIN OF THE N-TYPE FIELD-EFFECT IN POLYANILINE AND OLIGOANILINE THIN-FILMS

We analyse the n-type field effect recently reported for protonated, l ayer-by-layer self-assembled polyaniline and oligoaniline thin films. An agreement is obtained between the experiments and a model, valid fo r three-dimensional variable-range hopping in a parabolic Coulomb gap. The results suggest that the wave-function decay length xi and/or the dielectric constant epsilon vary with the position of the Fermi level (E-F), with a positive derivative d{ln[xi(E-F)epsilon(E-F)]}/dE(F) in the order of a few eV(-1). The apparent discrepancy between the p-typ e doping and n-type field effect is explained by the electron-hole asy mmetry characteristic for aniline derivatives.