Activation energies and electron transport in LDPE

Space charge measurements were made on low density polyethylene samples to which dc fields had been applied. Some measurements were performed under isothermal conditions, and others with a temperature gradient established across the sample thickness. Isochronal current density. was also measured as a function of temperature and field. The activation energy associated with the hopping transport of electrons through the sample volume was around 0.09 eV, whereas the activation energies deduced from the temperature dependence of the isochronal current density were in the range 0.60-1.40 eV, depending on the applied field strength and the impurity content of the samples. It was concluded that the isochronal current densities were controlled by electron injection from the cathode, the most likely injection mechanism being tunnelling between the Fermi level of the metallic electrode and acceptor sites within the dielectric close to the interface.