Single-photon detectors are essential for a range of quantum technology applications such as quantum communications, quantum optics and photonic quantum information processing applications. They can also provide significant benefit compared to coventional p-i-n and linear avalanche photodetectors (APDs) for a range of applications including range-finding, Light Detection And Ranging (LiDAR), facial recognition and covert imaging analysis. CMOS SPADs have been commercially available for many years but the bandgap of silicon precludes operation beyond about 1 µm wavelength. We have been adding Ge absorbers onto Si avalanche regions to allow SPADs to operate at the longer wavelengths required for telecommunications and which provides signficant benefits for LiDAR.
We have been working with Gerald Buller's group at Heriot-Watt University to pioneer Ge on Si SPADs and we jointly demonstrated the first Geiger mode Ge on Si SPADs operating at both 1310 nm and 1550 nm wavelengths. More recently we have demonstrated record single photon detection efficiencies (SPDE) up to 38% and made the first short-wave (SWIR) LiDAR using Ge on Si SPADs at 1450 nm wavelength. We are part of two InnovateUK projects AquaSec aiming to improve the devices for quantum communications applications and SPIDAR to produce imaging arrays integrated with read out integrated circuits to allow LiDAR for a range of applications including automotive driver aids, autonomous vehicles, analysing earthworks for potential landslips and military applications.