Hot Electron Generation in Silicon Micropyramids Covered with Nanometer-Thick Gold Films for Near-Infrared Photodetectors

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.