Plasmonic enhanced silicon pyramids for internal photoemission Schottky detectors in the near-infrared regime

We demonstrate a nanoscale broadband silicon plasmonic Schottky detector with high responsivity and improved signal to noise ratio operating in the sub-bandgap regime. Responsivity is enhanced by the use of pyramidally shaped plasmonic concentrators. Owing to the large cross-section of the pyramid, light is collected from a large area which corresponds to its base, concentrated toward the nano apex of the pyramid, absorbed in the metal, and generates hot electrons. Using the internal photoemission process, these electrons cross over the Schottky barrier and are collected as a photocurrent. The combination of using silicon technology together with the high collection efficiency and nanoscale confinement makes the silicon pyramids ideal for playing a central role in the construction of improved photodetectors. Furthermore, owing to the small active area, the dark current is significantly reduced as compared with flat detectors, and thus an improved signal to noise ratio is obtained. Our measurements show high responsivities over a broad spectral regime, with a record high of about 30 mA/W at the wavelength of 1064 nm, while keeping the dark current as low as ∼100 nA. Finally, such detectors can also be constructed in the form of a pixel array, and thus can be used as focal plane detector arrays.