Heterojunction diodes comprising poorly (1 at. %) nitrogen-doped n-type ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films and p-type Si substrates were prepared in nitrogen and hydrogen mixed gas atmosphere by coaxial arc plasma deposition. Dark current density-voltage (J-V) characteristics were studied in the temperature range of 200-400 K, in order to investigate the current transport mechanism through the fabricated heterojunctions. The temperature dependence of the ideality factor and reverse saturation current reveals that carrier transport predominantly occurs in the generation-recombination mechanism and, at low temperatures, it accompanies tunneling via weak traps. The heterojunctions surely exhibited photodetection for 254nm ultraviolet light illumination. It is expected that photocarriers will be generated at UNCD grains and transported through an a-C:H matrix.
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