Temperature dependence of dispersive hopping transport and diffusion in disordered solids |
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Authors: | William H. Hamill |
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Affiliation: | Department of Chemistry and Radiation Laboratory, University of Notre Dame, Notre Dame, IN 46556, U.S.A. |
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Abstract: | The time- and temperature-dependent drift mobility μd for dispersive transients in disordered solids is in terms of distance L, field E and transit time tT. Since current I ∝ tsu?(1?α) for t <Tand 0<α<1 by Scher-Montroll theory for hopping among localized states, it follows that where τ≈ 10?13s is estimated. Further and the activation energy Δ0 is time independent. On this basis Δ for the carbazole polymers is ca. zero, that for a-Se is ca. 0.05 eV, and that for a-As2Se3 is 0.35 eV rather than 0.5, 0.3 and 0.6 eV respectively on a phenomenological basis for μd(T,t). Trap-controlled hopping transport may be excluded. Time-resolved optical studies of excess carrier recombination supplement mobility measurements in a-Si:H and a-As2Se3 as well as other systems. Combined results suggest a dielectric response mechanism in which the time-dependent hopping frequency of localized carriers ν ∝ tα?1 arises from distortion of the medium at localization sites. This is satisfied by Δ(T,t) = Δ0+(1?α)KTT ln(t/τ) where τ is the mean initial localization time of the carrier, 10?13?10?12s, Δio is the height of the barrier at T, and 0<α0(t/τ)α?1 exp(frsol|?Δ0/KT) which applies also to bimolecular recombination. |
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