Longwave-infrared Avalanche Detectors with Superlattices (LANDS)

The US Army needs high sensitivity, fast infrared detectors for a variety of military applications such as laser radar and 3D range imaging.Ā Infrared detectors with internal gain can suppress circuit noise and offer enhanced sensitivity for applications for detection, identification and tracking of man-sized objects. Avalanche photodetectors (APD) provide multiplication gain due to impact ionization of carriers.Ā This gain can improve system-level signal-to-noise ratio (SNR) in cases where the detector signal is otherwise too low and overwhelmed by noise in down-stream amplifiers and read out integrated circuits (ROICs).Ā Most current APDs are limited either to visible (using Si), near-infrared (NIR, using Si or InGaAs), or short-wave infrared (SWIR, using InAs) wavelengths.Ā For longer wavelength APDs, the incumbent technology is mid-wave infrared (MWIR) HgCdTe that has large gains with exceptionally low excess noise due to the fortuitous electronic band-structure.Ā However, these detectors need to be cooled below 100 K due to their large dark current.Ā Moreover, HgCdTe detectors suffer from ō-abilityö arguments (manufacturability, reproducibility, availability, affordability, scalability, non-uniformity, etc.). ĀIn the past decade, there have been significant advances in the development of MWIR and LWIR Type II Superlattice (T2SL) detectors with unipolar barrier heterostructures such as nBn, pBp, and complimentary barrier infrared detectors (CBIRD) detectors.Ā The US department of defense advanced the technology readiness level of the T2SL detectors through an Army lead coalition ofĀ industrial partners called the Vital Infrared Sensor Technology Acceleration (VISTA).Ā However, these standard heterostructures do not have internal gain.Ā III-V T2SL technologies in a SACM structure provide a large degree of flexibility in noise reduction by band-structure engineering (E-k dispersion) of the impact ionization coefficients, and band-diagram engineering (E-x diagram) by heterostructure engineering of the layers in the stack.