Leonardo UK high-performance shortwave avalanche photodiode arrays for astronomy

Scientific applications, such as astronomy or Earth observation from low-Earth orbits, often involve extreme operating conditions, such as very long wavelength or 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 vapor 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 quantum efficiency. We focus on astronomy because this field has the most extremely low photon flux levels (>0.01 photons/pixel/s). In particular, linear-mode avalanche photodiode arrays 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 is reported. First, for future adaptive optics systems, a 512×512/24-μm sensor with frame rates over 2000 frames/s is described, aimed initially at the Extremely Large Telescope. Second, the progress on high-speed avalanche photodiode arrays mainly for free-space optical communications and light detection and ranging is summarized.