Temperature-dependent conductivity and Hall measurements have been carried out on heavily in situ B-doped polycrystalline diamond films in a temperature range from ∼100 to 750 K. The slope of the conductivity is clearly non-Arrhenius leading to a pronounced tail at low temperatures. Carrier transport at low temperatures is dominated by variable range hopping. The activation energy decreases with increasing doping concentration and the most heavily doped diamond films show metallic behavior above room temperature. Hole carrier concentrations up to 1.8×1021 cm−3 were measured in agreement with secondary-ion-mass spectroscopy investigations.

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