Short-Wave Infrared HgCdTe Electron Avalanche Photodiodes for Gated Viewing

Short-wave infrared (SWIR) HgCdTe electron avalanche photodiodes (eAPDs) with different doping profiles have been characterized for use in SWIR gated viewing systems. Gated viewing offers enhanced image contrast in scenes with clutter from the foreground or background. HgCdTe-based eAPDs show exponential gain–voltage characteristics and low excess noise and are, therefore, well suited for active imaging applications. The gain achievable at a fixed reverse voltage varies with the bandgap of the Hg1−xCdxTe detector material. We analyze current–voltage and gain–voltage plots measured on SWIR Hg1−xCdxTe eAPDs with x = 0.45, corresponding to a cutoff wavelength of 2.55 μm at 150 K. The cutoff has been chosen as a trade-off between achievable APD gain and operating temperature for SWIR gated-viewing systems with target distances of about 1000 m. Focal plane arrays with a readout-integrated circuit featuring a fast internal clock have been built and their performance with respect to gated viewing applications has been evaluated on a laboratory demonstrator for short distances. Future plans for a field demonstrator for distances up to 1000 m are described briefly at the end.