N-Type nanocrystalline iron disilicide/intrinsic ultrananocrystalline diamond/amorphous carbon composite/p-type Si heterojunction photodiodes were successfully fabricated using pulsed laser deposition and coaxial arc plasma deposition. Their current-voltage (I-V) curves were measured at low temperatures ranging from 300 K to 60 K. The possible carrier conduction mechanisms were determined by analyzing the dark I-V curves. The NIR photodetections were evaluated using a 1.31 μm laser. The dominant conduction mechanisms through the heterojunctions from 300 K to 200 K and 180 K to 60 K were recombination and trapassisted multi-step tunneling processes, respectively. At 60 K, the difference in ratio between photocurrent and dark current was three orders of magnitude, with detectivity of 1.10×1011 cm Hz1/2/W at zero bias voltage, which was comparable to the existing values of commercial NIR photodiodes at the same temperature.
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