Analysis of conductivity dependence on temperature and frequency has demonstrated to be a powerful tool to infer the electrical properties of nanostructured materials. Such approach enables to evaluate charge transport mechanisms and discriminate grain boundary and grain interior contributions to their limitation. Different contributions can be identified and separated by reference to a physical model also using equivalent electric schemes suitable to address the whole DC and AC electrical response. The paper is aimed to report on the work carried out on intrinsic and lightly nitrogenated ultrananocrystalline diamond (UNCD) deposited by a microwave assisted CVD process using Ar/H2/CH4/N2 gas mixtures [1]. Thin films on silicon were investigated in DC and AC regime in the range 10 mHz-10 MHz at different temperature in the 115K - 550K range. The electrical response has been modeled either by a series or a parallel equivalent scheme also considering the contribution of a contact resistance in series with the equivalent material?s scheme. These schemes fairly agree with the experimentally observed low-frequency data, but cannot completely explain trends observed in the high-frequency range. Effects associated to the formation of a distributed junction at the interface of the p-type nanocrystalline diamond grain and n-type grain boundary is proposed to justify observed trends.

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