Giant photoconductivity induced by plasmonic Co nanoparticles in Co-doped amorphous carbon/silicon heterostructures

A giant photoconductivity was observed in heterostructures of Co-doped amorphous carbon/silicon (Co–C/Si), which were fabricated by growing Co–C films on n-type Si substrates through pulsed laser deposition (PLD). When the sample was illuminated by a monochromatic light with a small density of 1 mW/cm2, the obtained photosensitivity, defined as the ratio of the photoconductivity σp to the dark conductivity σd, was as large as ∼105. Spectral dependence of the photoconductivity demonstrated significant photosensitivity in a large spectrum range and exhibited a peak photosensitivity around ∼710 nm. Transmission electron microscopy (TEM) revealed self-assembled cobalt nanoparticles in the amorphous carbon layer. In comparison with Co–C/Si heterostructures, the pure amorphous carbon (a-C)/Si heterostructure without Co nanoparticles was also fabricated and no significant photoconductivity was found. The mechanism of giant photoconductivity might be attributed to the surface plasmon resonance (SPR) absorption of Co nanoparticles.