Variable range hopping revisited: the case of an exponential distribution of localized states

Numerical modeling of single-phonon hopping transport within distributions of localized electronic states shows that many transport data for amorphous semiconductors and polymers are consistent with exponential tail state distributions rather than with Mott's hypothesis of an energy-independent distribution near the Fermi level. Although both cases lead to a T-14 temperature dependence of the 3D hopping conductivity. they can be discriminated by their different correlations between the slope and the conductivity prefactor. This numerical approach allows a determination of the localization parameter N(E-F)gamma(-3). where (1/gamma) is the decay length of the electronic wave function, and the assessment of the validity conditions for the single-phonon approximation. (C) 2002 Elsevier Science B.V. All rights reserved.