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Electronic hopping transport mechanism in polyethylene

Experiments of dc-conduction and dielectric breakdown in polyethylenes with different amounts of carbonyl groups incorporated in the polymer chain have been performed to elucidate the nature of conduction in the polymer. The experiments show that the dipolar C=O-groups are the localized states acting as hopping sites in an electronic transport process. According to the random distribution of hopping sites the transport of elections may be described by a distribution of hopping probabilities. A comparison with details of the experiments shows that the currents are not only space-charge-limited, but also injection-controlled. One consequence of the random distribution of hopping sites is, that an increasing amount of electrons arrives at sites with very low escape probabilities. This means that after switching off the electric field there exists a long-lived space charge within the polymer, which can only be driven out by heating the polymer.