Leonardo UK infrared sensors for scientific applications

Scientific applications, such as, astronomy or Earth observation from low-Earth orbits, often involve extreme operating conditions, requiring state-of-the-art performance parameters with very low photon arrival rates. These present a technical challenge for infrared sensor manufacturers, in particular dark current. The infrared detector technology at Leonardo UK is well suited to these challenges due to bandgap-engineered HgCdTe, grown by Metal Organic Vapour Phase Epitaxy (MOVPE). By widening the bandgap in critical parts of the sensor the dark current can be effectively switched off. Each diode is physically separated in a mesa process giving market-leading resolution, crosstalk and inter-pixel capacitance. The structure also provides 100% fill-factor and 100% internal QE. This paper focusses on astronomy because this field has the most extreme low photon flux levels (less than 0.01 photons /pixel/second). In particular, linear-mode avalanche photodiode arrays (LmAPDs) are vital for astronomy to amplify the single-photon response above the noise floor. The design and performance of the detectors for astronomy is a particularly good example of bandgap-engineering using MOVPE. Progress in two other fields are reported. Firstly, for future adaptive optics (AO) systems, a new 512×512/24 μm sensor with frame-rates over 2000 frames/s is described, aimed initially at the Extremely Large Telescope (ELT). Secondly, the progress on high speed (GHz) APDs mainly for free-space optical communications and LIDAR is summarised.