High-field electrical conduction has been studied in undoped polycrystalline diamond over a wide temperature range. The current increases exponentially with the electric field with an exponential factor which increases linearly with the inverse of temperature. The activation energy of the conductivity is found to be strongly field dependent and to decrease linearly with the electric field. The experimental data support a Poole–Frenkel conduction with overlapping centers. The centers are found to be located at around 1.1 eV from the band edge with a density of about 2×1017 cm−3.

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