Ge-on-Si SPADs for Quantum Communications

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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 com- pared to conventional 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 Single Photon Avalanche Diodes (SPADs) have been commercially available for many years, but the band gap of silicon limits operation using light beyond approximately 1 um in wavelength. Adding germanium absorbers onto silicon avalanche regions allows SPADs to operate at the longer wavelengths required for telecommunications and which provides significant benefits for LiDAR as systems can operate with greater accuracy in the presence of obscurance and precipitation. Further to this, Ge-on-Si SPADs have the potential to be over 200 times cheaper than the present commercial technologies available, meaning that this area of research is receiving interest from major automotive manufacturers and telecommunication companies from around the world. The research proposed for this project will continue to develop work being undertaken at the Semiconductor Devices Group at Glasgow by delivering a new design of Ge-on-Si SPAD devices which can be easily coupled to optical fibres for use in quantum key distribution and quantum communication test systems. The Semiconductor Devices Group at the University of Glasgow is the global pioneer of such devices and has a significant lead in this silicon-based technology at short wave infrared wavelengths, demonstrating the first Ge-on-Si SPAD photodetectors and more recently record-breaking single photon detection efficiencies (SPDE). Being able to replicate this level of detection efficiency and improve other key Figures of Merit (FOMs) such as afterpulsing, jitter and Noise Equivalent Power (NEP) will be crucial to producing a new design that is suitable for use in quantum systems. The work will include designing devices, being trained to fabricate devices in the James Watt Nanofabrication Centre and the characterisation of the devices using electronic and optical techniques to determine their performance. There will be engagement with top researchers in academia and collaborators in the UK Quantum Communications Hub and UK industry to understand the end user performance requirements as well as to test successfully developed devices in real systems.