Leonardo UK development of linear mode midinfrared wavelength APD array technology for high- and low-photon flux applications

Leonardo UK Short Wave InfraRed (SWIR) avalanche photodiode (APD) array technology has been expanded to target the Mid-Wave InfraRed (MWIR) waveband. HgCdTe (MCT) material developed using Metal Organic Vapour Phase Epitaxy (MOVPE) grown on low-cost gallium arsenide (GaAs) substrates has been designed for high speed and high sensitivity by engineering the band gap of the MCT heterostructure, crucial in APD designs to minimise excess noise. A Separated Absorber Multiplication (SAM) region design has been designed with absorber band energies corresponding to MWIR wavelengths and evaluated against an extended cut off Short-Wave (SW) APD design. Focal Plane Arrays (FPAs) have been created by hybridising the MCT to both a readout integrated circuit (ROIC) designed for high-speed SW-APDs and a ROIC designed for use with MW detectors, and a comparison between spectral performance and responsivity covering the 3 – 5 μm range has been evaluated in initial trials. In addition, dark current has also been assessed for both MCT designs. This paper reports a comparison of results for two MW-APD structures on two distinct ROIC architectures. Application spaces including integration of an APD to standard mid wave imaging and flux-starved terrestrial and space environments are considered.