Low temperature transport phenomena in lightly nitrogenated ultrananocrystalline diamond

Impedance spectroscopy of lightly nitrogenated ultrananocrystalline diamond films is investigated in the range 10 mHz-10 MHz at different temperatures between 115 K and 300 K. The electrical response was modeled alternatively by a series and a parallel equivalent scheme considering also the contribution of a resistance in series with the material's response. These schemes fairly agree with experimentally observed low-frequency data, but cannot completely explain trends observed at higher frequencies. Resonance effects were indeed evidenced due, probably, to the formation of a distributed junction at the interface between the p-type nanocrystalline diamond grain and the degenerate n-type connective tissue. The role of the series resistance is discussed and a physical model is proposed to justify the resonant behavior of the quality factor.