CURRENT-TEMPERATURE ANALYSIS OF DC GLOW-DISCHARGE CVD DIAMOND FILMS

We have investigated the electrical transport properties in CVD diamon d films prepared with a DC plasma glow discharge method. The analyzed samples have been grown with different methane concentrations and subs trate temperatures; the resulting resistivities at room temperature ar e in the range from 7.10(8) Ohm.cm to 2.10(13) Ohm.cm. The current has been measured as a Function of the temperature, in the region from li quid nitrogen to 700 K. The electrical conduction process has been fou nd to depend strongly on the temperature range considered. For T>600 K , the conductivity can be described as an exponential function of the reciprocal temperature: in this region, two samples with the highest r esistivities, show an activation energy of 1.7 eV. This value is relat ed to the donor impurity of isolated nitrogen which has been detected by electron spin resonance analysis. A variable range hopping process is proposed to describe the experimental conductivity in the low tempe rature region. Material characterization performed with micro-Raman sp ectroscopy and electrical measurements depict the transport process as a conduction due to low resistivity graphite-like phases mainly prese nt along grain boundaries. (C) 1998 Elsevier Science Ltd. All rights r eserved.