Effect of nitrogen on the electronic properties of ultrananocrystalline diamond thin films grown on quartz and diamond substrates

The electronic transport properties of ultrananocrystalline diamond thin films grown from an argon-rich Ar/CH4 microwave plasma have been investigated in the temperature range from 300 up to 700 K and as a function of nitrogen added to the gas phase (from 0 to 20%). The influence of nitrogen incorporation on the electronic transport properties of the ultrananocrystalline diamond films was examined by conductivity and Hall effect experiments. Electron spin resonance and electrically detected magnetic-resonance measurements complement the electronic transport study. In the case of films grown with a high nitrogen content in the gas phase, it was possible to perform Hall effect experiments, which showed n-type conductivity, with carrier concentrations up to 10(20) cm(-3) and mobilities above 1 cm(2)/V s at room temperature. From the temperature dependence of the conductivity, we propose that electron transport via grain boundaries can explain the high conductivity (up to 150 Omega(-1) cm(-1)) of nitrogen containing ultrananocrystalline diamond films. The conduction mechanism in these films is explained by a transition from variable range-hopping transport in localized states near the Fermi level (in the case of low-conductivity films) to defect band conduction (in the case of high-conductivity films). The results have been discussed using a hopping model which assumes an exponential distribution of the density of states near the Fermi level, in order to explain the temperature dependence of the conductivity in the temperature range from 300 up to 700 K. Electrically detected magnetic resonance confirms that the transport of the low-conductivity samples can be explained by hopping via carbon dangling bonds.