Assessment of HgCdTe and GaAs/GaAlAs technologies for LWIR infrared imagers

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Abstract
Imagery of long wavelength infrared HgCdTe and GaAs quantum well staring arrays in size 128 X 128 has been demonstrated. In this paper, we compare detector array performance characteristics, discuss the natural and technological limitations of both technologies and identify the improvements likely to be made in the near future. At this stage of feasibility demonstration in the spectral band 8 - 10 micrometers , the effective quantum efficiency in GaAs FPAs is 4% compared to 60% for HgCdTe and the responsivity is 0.08 A/W compared to 4.5 A/W. This value of 0.08 A/W is significantly below the value 2 A/W reported for single quantum well infrared photodetectors (QWIP) detectors. The peak detectivities and NE(Delta) T at 78 K are (5 X 109 cm (root)Hz/W, 0.037 K) and (2 X 1011, 0.005 K) for QWIP and HgCdTe, respectively. The residual nonuniformities after two-point correction are < 0.01% for QWIP arrays and 0.012% for HgCdTe. Crosstalk is currently unsatisfactory in QWIP detector arrays, but design concepts can be used to reduce this effect. For terrestrial imaging, GaAs quantum well detector arrays most likely will need to operate at temperatures below 80 K from fundamental considerations; HgCdTe detector arrays are background limited at operating temperatures b 12 ph/cm2-sec, QWIP detectors at 40 K are background limited. This observation plus their radiation hard characteristics suggest a possible niche in strategic applications.

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