Gated IR Imaging with 128 × 128 HgCdTe Electron Avalanche Photodiode FPA

Abstract

The next generation of infrared (IR) sensor systems will include active imaging capabilities. One example of such a system is a gated active/passive system. The gated active/passive system promises target detection and identification at longer ranges compared to conventional passive-only imaging systems. A detector that is capable of both active and passive modes of operation opens up the possibility of a self-aligned system that uses a single focal plane. The mid-wave infrared (MWIR) HgCdTe electron injection avalanche photodiode (e-APD) provides state-of-the-art 3 lm to 5 lm performance for the passive mode and high, low-noise, gain in the active mode, and high quantum efficiency at 1.5 lm. Gains of greater than 1000 have been measured in MWIR e-APDs with a gain-independent excess noise factor of 1.3. This paper reports the application of the mid-wave HgCdTe e-APD for near-IR gated-active/ passive imaging. Specifically a 128 · 128 focal-plane array (FPA) composed of 40-lm-pitch MWIR cutoff APD detectors and custom readout integrated circuit was designed, fabricated, and tested. Median gains as high as 946 at 11 V bias with noise equivalent photon inputs as low as 0.4 photon were measured at 80 K and 1 ls gate times. This subphoton sensitivity is consistent with the high gains, low excess noise factor, and low effective gain normalized darkcurrent densities, near or below 1 nA/cm 2 , that were achieved in these FPAs. A gated imaging demonstration system was designed and built using commercially available parts. High resolution and precision gating was demonstrated in this system by imagery taken at ranges out to 9 km.

SWIR HgCdTe avalanche photiode focal plane array performances evaluation

“…The F definition detailed later implies that a F value below 1 is not physic. A difference between the true F and the measured value has ever been observed by DRS [4]. The origin of this difference was explained by a variation of the pixel fill factor when the photodiode is biased.…”

HgCdTe APDS for space applications

“…Such performances have been demonstrated in HgCdTe APDs with x Cd lower than 0.5. The HgCdTe APDs do also have low dark currents at high gains [7], [8] and a response time which is close to independent of the gain [9]- [12]. The latter is again related to exclusive electron multiplication, which guarantees that the response time is limited by a single transit time of the depletion region width for each type of carrier [9]- [12].…”

“…These characteristics are complemented by a high gain homogeneity which makes HgCdTe APDs suitable for imagery application. Consequently, high performance focal plane arrays have been developed for active [2,6,7,[13][14][15][16][17] and passive imaging [14,18]. Four HgCdTe APD FPAs have been developed at CEA/Leti and Sofradir so far [15][16][17][18].…”

Review of ladar: a historic, yet emerging, sensor technology with rich phenomenology

“…Sensitivity for 3-D mapping will currently tend to not be single photon, but there is development in that direction. [26][27][28][29][30][31] Figure 4 shows gated imagery through a sand cloud, from an ASC 3-D imager. 32 Raytheon and DRS have made significant progress in developing high sensitivity linear mode APD arrays.…”