Silicon based single photon avalanche diodes (SPAD) are already a valuable technological solution to detect and accurately measure photons. Arranged in in extended arrays as Silicon Photomultipliers (SiPM), they can provide both single-photon counting sensitivity and fast responsivity in large-area detectors. However, some of their promising applications (LiDAR and 3D-ranging imaging at 850÷950 nm wavelengths, spectroscopy with red and near infra-red – NIR – lasers, quantum computation, readout of NIR emitting scintillator crystals) are not yet fully exploited due to the limited Si NIR absorption coefficient. The latter implies absorption depths much larger than the typical active thickness of Si SPADs and SiPMs (10÷100 μm against ~μm) resulting in a detection efficiency too low for most of the previous applications.
The aim of this project is to integrate plasmonics nanostructures on state-of-the-art SPADs/ SiPMs to extend their attractive performances to the range of NIR/ infrared radiation keeping an excellent temporal resolution. The exploitation of Surface Plasmon Polaritrons will convert light in highly-confined modes and enhance the absorption of NIR photons. Noble metal (mainly Ag) nanodot arrays and nano-gratings will be integrated on thin Si photodetectors passivated with a thin dielectric film exploiting semiconductor fabrication methodologies including electron beam lithography for the definition of nanostructures on some prototypes.
The process can then be easily brought to an industrial scale production using standard processes for the fabrication of integrated circuits (IC). This new device can provide an astonishing enhancement of NIR detection efficiency (photon detection efficiency up to ~30 % at 950 nm) via light coupling in plasmonic modes. Furthermore, using thin Si substrates leads to an improved temporal resolution, which turns out in a finer depth resolution for LiDAR (Laser imaging detection and ranging) and time-of-flight imaging applications, important for smart and green automotive applications.