Near infrared single photon detection using Ge-on-Si heterostructures

Semiconductor-based photon-counting detectors have risen to prominence in the last decade as new application areas have emerged, such as quantum information processing, and in particular quantum cryptography. These photon-counting detectors - mainly fabricated from silicon - have also taken over from photomultipliers in a number of laboratory applications where their room temperature operation, fast timing, small footprint and low power consumption have proved advantageous in a host of applications, for example fluorescence lifetime imaging. New photon-counting applications areas in ground-based, airborne and even satellite-borne laser-induced reflection techniques have been developed in recent years (eg for detection of trace gas concentrations), as well as significant developments in low-power optical imaging and high-resolution depth imaging. In the near-infrared spectral region - where silicon-based detectors are highly inefficient - there remain substantial issues with available single-photon avalanche diode (SPAD) detectors. Their performance deteriorates due to the high noise levels associated with thermal excitation of carriers across the relatively narrow bandgaps, as well as the effects of mid-gap trapping centres causing the deleterious effects of afterpulsing, further contributing to detector noise levels. This project aims to establish a new class of germanium/silicon SPADs that will operate efficiently in the near-infrared, particularly at the strategically important telecommunications wavebands, and combine the advantages of low-noise Si single-photon avalanche multiplication with the infra-red sensing capability of Ge. This new class of detectors will take advantage of recent advances in epitaxial Ge/Si growth and be fabricated in conjunction with the recently-created UK Silicon Photonics consortium (UKSP), which offers world-class device growth and fabrication facilities. The detectors will be validated on existing state-of-the-art testbeds for quantum key distribution and time-of-flight ranging/depth imaging. The project leverages the combined expertise and facilities of existing UK Silicon Photonics consortium to do additional and new work, thus adding value to that consortium.

Engagement with non-academic beneficiaries - In order to engage with non-academic beneficiaries, the consortium will publicise results via articles in general photonics industry publications, such a Opto-Laser Europe or Laser Focus World, as well as the mainstream academic journals like Nature Photonics and Optics Express. The consortium will also construct and maintain a project web-site, linking to collaborators' sites and the UK Silicon Photonics site, as well as providing content for other specific single-photon sites (eg www.photoncount.org/). Engagement with end-users - The consortium already have strong connections with the end-user beneficiaries, several with whom we already have formal connections: These end-users include: (1) Existing developers of SPAD technology: The consortium have strong existing links with current developers of SPAD technology, inclusing MPD (Italy) and Princeton Lightwave (USA). Assuming that the project is successful, there are several possibilities for commercial exploitation: (1) a licensing agreement with a current SPAD manufacturer; (2) a licensing agreement with larger semiconductor photonics companies not currently active in the photon-counting field; and (3) a fab-less spin-out company initiated by the consortium. (2) Users of LIDAR and depth imaging systems: The consortium has good links with several end-users of SPAD technology in the LIDAR including Selex Gallileo (see attached letter of support) and the European Space Agency (see attached letter of support). The consortium will engage with these sectors during the course of the project, to discuss exploitation of these detectors in these sectors. (3) Developers and users of quantum key distribution systems: The consortium has strong links with the quantum information community and is well-placed to exploit project developments in this field. Of most immediate interest is the application of quantum key distribution, and the consortium has links with several companies commercialising this technology (see attached letter of support from Toshiba). Exploitation Processes - The commercial potential of the proposed research is clear and the project team will take care to protect intellectual property via their technology transfer / innovation offices. All the universities have spin-out experience in relevant technology sectors, e.g. Heriot-Watt and Surrey in photonics, Surrey in space systems, Warwick in semiconductor growth technology and Leeds in sensors. Within the team of consortium Investigators there is excellent experience in licensing and university spin-out company formation. Capability - The impact activities will be co-ordinated overall by Prof. Buller and led by PIs at each site. However, we believe that the diverse commercial relevance of the project presents extensive training opportunities in knowledge transfer skills for the research fellows and students involved in the work. We will ensure that these researchers are involved in interactions with end-users and potential manufacturers and encourage them to develop initiative in engagement with beneficiaries. This experience will significantly enhance the career development of the 7 early-stage researchers due to work on the project. In addition, we will seek industrial secondment for researchers as appropriate (e.g. for SPAD testing at end-user sites) and will secure industrial and other (e.g. Knowledge Transfer Secondment scheme) funding for this activity.