Hopping conduction in high electric fields: three issues

David Emin

doi:10.1117/12.254241

15 October 1996 Hopping conduction in high electric fields: three issues

David Emin

Proceedings Volume 2850, Organic Photorefractive Materials and Xerographic Photoreceptors; (1996) https://doi.org/10.1117/12.254241
Event: SPIE's 1996 International Symposium on Optical Science, Engineering, and Instrumentation, 1996, Denver, CO, United States

Abstract

Three issues concerning phonon-assisted hopping in molecularly doped polymers are considered. The first issue is whether Arrhenius jump rates in the vicinity of room temperature arise from single-phonon or small-polaronic hopping. It is concluded that Arrhenius hopping only occurs above low temperatures through small-polaronic hopping. Second, hopping in molecularly doped polymers is compared with small-polaronic hopping of other systems. Small- polaronic hopping typically occurs between similar chemical structures whose energies are relatively insensitive to their surroundings. Thus, disorder energies experienced by carriers are often modest, values of several hundredths of an eV are common. Nonetheless, the effects of large electric fields on carrier mobilities differ significantly among disordered systems. Data reported for molecularly doped polymers is unlike that for either transition-metal-oxide or chalcogenide glasses. In no case is high-field transport well understood. Finally, I stress that steady-state flow is driven by differences in sites' quasielectrochemical potentials (QECPs). With disorder, differences of QECPs are not simply related to the driving emf. Solution of the (nonlinear) stochastic equations for the QECPs shows that bottlenecks produced by disorder result in nonohmic conduction. Solving the linearized stochastic (disordered resistor network) equations underestimates bottleneck effects. Linearization is inappropriate when intersite differences in the QECPs exceed (kappa) T.

Citation Download Citation

David Emin "Hopping conduction in high electric fields: three issues", Proc. SPIE 2850, Organic Photorefractive Materials and Xerographic Photoreceptors, (15 October 1996); https://doi.org/10.1117/12.254241

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