The heterojunction between metal and silicon (Si) is an attractive route to extend the response of Si-based photodiodes into the near-infrared (NIR) region, so-called Schottky barrier diodes. Photons absorbed into a metallic nanostructure excite the surface plasmon resonances (SPRs), which can be damped non-radiatively through the creation of hot electrons. Unfortunately, the quantum efficiency of hot electron detectors remains low due to low optical absorption and poor electron injection efficiency. In this study, we propose an efficient and low-cost plasmonic hot electron NIR photodetector based on a Au nanoparticle (Au NP)-decorated Si pyramid Schottky junction. The large-area and lithography-free photodetector is realized by using an anisotropic chemical wet etching and rapid thermal annealing (RTA) of a thin Au film. We experimentally demonstrate that these hot electron detectors have broad photoresponsivity spectra in the NIR region of 1200-1475 nm, with a low dark current on the order of 10 A cm. The observed responsivities enable these devices to be competitive with other reported Si-based NIR hot electron photodetectors using perfectly periodic nanostructures. The improved performance is attributed to the pyramid surface which can enhance light trapping and the localized electric field, and the nano-sized Au NPs which are beneficial for the tunneling of hot electrons. The simple and large-area preparation processes make them suitable for large-scale thermophotovoltaic cell and low-cost NIR detection applications.

Plasmonic metallic nanostructure/silicon composites are gaining increasing attention due to their NIR photodetection capability and potential compatibility with CMOS technology. However, those kinds of photodetectors suffer from low efficiency due to the low optical absorption and poor hot electron injection efficiency. Here, we propose an efficient and low-cost NIR photodetector based on a gold film coated silicon micropyramid, which was fabricated with the large-scale, lithography-free, chemical wet-etching process. We experimentally demonstrated that the proposed micropyramid enhanced the photoresponsivity for the NIR light by 3 times compared with that of the flat reference sample at 1300 nm. Besides, the micropyramid strategy allowed the photodetector to preserve the polarization-insensitive and incident-angle-insensitive photoresponse. Furthermore, we further increased the responsivity through the back-side illumination from the silicon side and carefully investigated the background mechanism by changing the thickness of the covered gold film. It is demonstrated that the enhanced responsivity is related to the location of the field enhancement (hot spots); the nearer to the Au/silicon interface, the higher the responsivity. These results indicate that the location of hot spots has a significant contribution to the hot electron injection efficiency and responsivity, and the simple wet-etching method is promising for large-scale and low-cost plasmonic hot-electron-based NIR photodetectors.

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Freestanding and transferable silica nanosheets with thicknesses of ≈5-7 nm are prepared via ethyl acetate-mediated hydrolysis of silica precursors in aqueous solution. The resulting silica nanosheets have shown many potential applications. For example, they can be used as the support film on the finer mesh grids for transmission electron microscopy imaging and as the precursor for the synthesis of silicon nanosheets.

Recent discoveries in the field of graphene-based heterostructures have led to the demonstration of high-performance photodetectors. However, the studies to date have been largely limited to the heterojunction with a Schottky barrier, restricted by an inevitable compromise between photoresponsivity and photodetectivity. Here, a new class of graphene-based tunneling photodetectors is introduced by inserting the Al 2 O 3 tunneling layer between silicon and graphene. The photocarriers can tunnel through the designed insulator layer which simultaneously blocks the dark current, thus maintaining high photodetectivity with desirable photoresponsivity. We further modulate the thickness of the Al 2 O 3 layer to explore the tunneling mechanism for the photocarriers, in which a photoresponsivity of 0.75 A/W, a high current ratio of 4.8 × 10 3 and a photodetectivity of 3.1 × 10 12 Jones are obtained at a 13.3-nmthick Al 2 O 3 layer. In addition, the fabrication process is compatible with conventional semiconductor processing, providing further flexibility to large-scale integrated photodetectors with high performance.