Plasmonic enhanced photodetectors for near infra-red light detection

Silicon based single photon avalanche diodes (SPAD) are able to detect single photons in the visible part of the spectrum with high detection efficiency and high timing resolution. They also provide both single-photon sensitivity and fast responsivity in large-area detectors if arranged in extended arrays as Silicon Photomultipliers (SiPM). However, in applications exploiting near infrared light like light detection and ranging (LiDAR), the detector performance is hindered by the limited Si absorption coefficient. The latter implies absorption depths much larger than the typical active thickness of these devices (10-100 μm against few micrometers) resulting in a quantum efficiency (QE) too low for most of the previous applications. The exploitation of Surface Plasmon Polaritrons (SPP) can convert light in highly-confined modes and enhance the absorption of NIR photons. In this contribution, the first results on the integration of plasmonics nanostructures on thin silicon photodiodes are reported. Electro-optical measurements were carried out and the QE has been measured in the full 400-1100 nm spectrum. The resulting QE on the first prototypes is higher than 7% at 950 nm, an enhancement of about 45% with respect to the reference structure, paving the way for the application of metallic nanograting to SPADs and SiPMs devices.