The recent discovery of electron initiated avalanche photodiodes (e-APD) using mercury cadmium telluride (MCT) semiconductor materials permitted a significant breakthrough in short wave (1-2.5 µm) infrared imaging. These diodes have an avalanche gain of up to 100 with an excess noise factor near 1, showing that the avalanche process is quasi deterministic. The hybridization of 320×256 e-APD arrays on silicon read-out circuitry permits to build imagers with fast readout rates (in the kHz range) while having at the same time a subelectron readout noise , which is a major improvement compared to previous infrared imaging technologies. The technology used to manufacture e-APDs is similar to the one used for standard HgCdTe diodes with a 100% fill factor, therefore a high quantum efficiency (typically QE=70-75 %) is maintained.
Today First Light Imaging makes this technology available to everybody: C-RED is opening a new era in terms of sensitivity and speed in the SWIR scientific cameras domain.
C-RED is using a unique 320×256 pixels HgCdTe e-APD array with 24 microns pixel pitch. The sensor cutoff wavelength is 2.5 microns and it allows sub-electron readout noise, taking advantage of the e-APD noise-free multiplication gain and non destructive readout ability. C-RED is also capable of multiple regions of interest (ROI) readout allowing faster image rate (10’s of KHz) while maintaining unprecedented subelectron readout noise.
The sensor is placed in a sealed vacuum environment and cooled down to cryogenic temperature (70K) using an integrated pulse tube, with a high reliability (MTBF > 90 000 h) much higher than standard stirling coolers used usually with cooled infrared arrays.
