Active matrix single-photon technologies on GaAs

The proposed research addresses the need for technologies able to detect single photons at infrared wavelengths, especially in the short-wave (SWIR) and mid-wave (MWIR) infrared. A number of electronic devices based on quantum phenomena, the so called "first" generation of quantum technology, are widespread and used every day for a number of applications. Research has recently shown that some quantum phenomena formerly considered mere scientific curiosities, such as particle entanglement, could have many interesting applications. A "second" generation of quantum technologies is therefore the subject of intense research effort, given their great potential for commercialisation. With regard to the imaging field, new advances in quantum technology include imaging of light in flight and detection of objects hidden behind corners. Such applications rely on cameras where each pixel is sensitive enough to detect single photons, and it consists of a silicon single photon avalanche detector (SPAD) achieved on the same chip as the addressing circuitry required. Silicon offers a commercially mature platform for SPAD-based cameras, but unfortunately on this material platform operation is limited to visible wavelengths. Imaging arrays of SPADs working at infrared wavelengths, not currently available, are highly desirable as they would unlock further applications in the field of industry asset management, biomedical imaging and environmental monitoring. The micro-system technology (MST) group at the University of Glasgow has pioneered MWIR imagers integrating indium antimonide (InSb) photodiodes (PDs) with gallium arsenide (GaAs) metal semiconductor field effect transistors (MESFETs) for addressing. Such imagers are able to operate at room temperature and as such they offer a robust and low-cost alternative to available devices in the MWIR wavelength range, which require cooling. Furthermore, most available MWIR imagers are based on hybridised technologies where PDs and addressing circuitry are attained on separate chips and then combined through flip-chip bonding, a costly and low-yield technique. Compound Semiconductor Technologies (CST) Global Ltd, leading the proposed research, will take the MWIR monolithic technology pioneered by Glasgow University and develop it into a robust manufacturing line aimed at commercialisation. The technology platform is extendable to provide functions at other wavelengths and in single-photon counting by appropriate selection of photo-active semiconductors. Gas Sensing Solutions (GSS) Ltd, a long-standing partner of CST Global Ltd and GU will lead the development of new materials to achieve SPADs at infrared wavelengths, supported by design and prototyping at GU.

This project on monolithic technologies working towards single-photon detection in the MWIR and SWIR wavelength ranges has potential for impact across several areas. The most immediate impact would be economic. Only cooled imagers are currently available in the 3 to 5 micrometers wavelength range, thus limiting their application to the defence and security market. The monolithic MWIR FPA technology pioneered by Glasgow University that will be translated into a manufacturing line aimed at commercialisation by CST has potential for room temperature operation, and as such excellent prospects to be fully adopted as core component by system manufacturers, e.g. MSquared Lasers Ltd and Thales Optronics that have expressed interest in the technology. Adoption of the proposed monolithic imagers by end users will support existing jobs and lead to creation of new positions both within the end user companies and the businesses involved with the manufacturing supply chain. Moreover, the proposed research exploits a compound semiconductor technology to deliver a monolithic MWIR imager, thus strengthening the UK compound semiconductor initiative and also Scottish initiatives such as the mid-infrared advanced growth epitaxy (MIRAGE). With its supply chain completely relying on Scottish businesses, this project will help to bring Scotland at the forefront of the £70 billion global sensing and imaging systems market, boosting significant economic growth.

In addition to commercial and economic benefits, through applications in the field of remote gas imaging and diagnostic imaging, monolithic MWIR FPAs have potential to improve human health and safety. A cost-effective way of imaging trace gases will find application not only for home safety and for the oil&gas industry, but also for monitoring urban air quality and pollution, as well as emissions from farms and landfills. An infrared diagnostic imaging tool will have the great advantage of not exposing patients to ionising radiation.

The environmental impact of the project is expected to be positive, for several reasons: first, a tool capable of remote gasimaging will be able to image and quantify greenhouse emission gases and pollutants; secondly, the monolithic MWIR technology will provide a mercury-free alternative to existing MIR imagers based on mercury cadmium telluride (known as
MCT), the toxicity of which is well known.