Plasmonic Nanostructures for Improved Photodetection

Plasmon nanostructures and metasurfaces have been intensely studied and applied in different applications, such as sensing, beam shaping, super-resolution imaging, energy harvesting, photocatalysis, and photodetection because they enable strong light absorption and scattering, and near-field amplification [1]–[3]. This work is focused on the development of low-cost solutions for improving the responsivity of photodetectors by integrating plasmonic nanostructures. We applied two methods: (1) generation of hot electrons, and (2) improvement of light absorption. The first method was used to extend the detection bandwidth of the Si photodetectors in the SWIR domain. We used n/n + Si wafers and a simple technology process: bottom Al electrodes deposited and patterned on the back-side (Ohmic contacts), and Schottky nanostructured contacts on the front side. The top electrodes consist of interconnected nano-islands that were obtained be depositing thin metal layers (e.g., Ag 15–50 nm thick) and thermal annealing, or by depositing very thin (4–8 nm) discontinuous metal layers. Examples of nanostructured electrodes are given in fig.la) and b). The incident sub-bandgap photons excite surface plasmons in the nanostructured electrode and generate plasmon-induced hot electrons. As the nanostructured electrode forms a Schottky barrier with Si, the hot carriers with energy greater than the Schottky barrier will be injected inject into the conduction band of silicon and generate a photo current well below the band edge of Si through the internal photoemission effect- IPE [3]–[5]. The nanostructured electrode acts as metamaterial absorber and thus it improved the efficiency of hot electrons generation. Responsivities greater than 7 mA/W @ 1310 nm was obtained with both Au and Ag nanostructured electrodes (table 1). A significant improvement, up to 50 mA/W @ 1310 nm, and up to 13.5 mA/W @ 1550 nm (higher than those recently reported ([3-5]) was obtained by combining finger electrodes (grating-like) with these nanostructured layers (table 1 and fig. 2).