A large format 1k×1k focal plane array (FPA) is realized using type-II superlattice photodiodes for long wavelength infrared detection. Material growth on a 3 in. GaSb substrate exhibits a 50% cutoff wavelength of 11 μm across the entire wafer. The FPA shows excellent imaging. Noise equivalent temperature differences of 23.6 mK at 81 K and 22.5 mK at 68 K are achieved with an integration time of 0.13 ms, a 300 K background and f/4 optics. We report a dark current density of 3.3×10−4 A cm−2 and differential resistance-area product at zero bias R0A of 166 Ω cm2 at 81 K, and 5.1×10−5 A cm−2 and 1286 Ω cm2, respectively, at 68 K. The quantum efficiency obtained is 78%.

Abstract-This paper presents a study of the performance degradation in a proton environment of very long wavelength infrared (VLWIR) HgCdTe detectors. The energy dependence of the Non-Ionizing Energy Loss (NIEL) in HgCdTe provides a framework for estimating the responsivity degradation in VLWIR HgCdTe due to on orbit exposure from protons. Banded detector arrays that have different detector designs were irradiated at proton energies of 7, 12, and 63 MeV. These banded detector arrays allo~ved insight into how the fundamental detector parameters degraded in a proton environment at the three different proton energies. Measured data demonstrated that the detector responsivity degradation at 7 MeV is 5 times larger than the degradation at 63 MeV. The comparison of the responsivity degradation at the different proton energies suggests that the atomic Columbic interaction of the protons with the HgCdTe detector is likely the primary mechanism responsible for the degradation in responsivity at proton energies below 30 MeV. Index Terms-HgCdTe detectors, Proton radiation effects, Non-Ionizing Energy Loss (NIEL)S PACE based infrared imaging systems place stringent performance requirements on very long wavelength ineared (VLWIR) detectors in terms of sensitivity, uniformity, operability, and radiation hardness. The radiation hardness goals for space based imaging systems are typically dominated by proton interactions with the FPA. The three sources of protons for space-based detectors include (1) protons in the inner Van Allen radiation belt, (2) the proton component of solar particle events and (3) hydrogen nuclei from intergalactic cosmic rays. Interaction of the protons with the HgCdTe detectors results in permanent performance degradation primarily due to total ionizing dose (TID) effects and displacement damage effects. The TID effects are generated by the loss of the kinetic energy &om an incident proton to ionization and primarily degrade the operation of readout integrated circuits (ROIC) through flat-band voltage shifts and increased leakage currents. Displacement damage effects result when a small amount of the proton energy is lost to nonionizing processes causing atoms to be removed from their lattice sites and form permanent electrically active defects. These displacement damage effects primarily degrade the performance of the HgCdTe detector array through increased dark current, reduction in responsivity, and degraded uniformity.Recent radiation results from VLWIR HgCdTe detector arrays [l] have shown a change in responsivity and lateral collection with increasing proton fluence. These measured data exhibit an exponential decrease in responsivity with increasing proton fluence. This loss in responsivity has been isolated to the detector, and its root cause is related to the detector design, which relies on lateral collection of charge to achieve high performance in quantum efficiency. It is this reliance on lateral collection that causes the loss of responsivity in a proton environment. For this detector stru...

An examination of the collective results from recent experiments quantifying the performance degradation rates of III-V-based, unipolar barrier infrared detectors with various designs and materials, cutoff wavelengths and operating conditions due to 63 MeV proton irradiation is presented. Empirical relationships were established between the radiation damage factors for dark current density, lateral optical collection length, and quantum efficiency and the inverse product of the detectors' cutoff wavelength and operating temperature. Fitting the dark current density damage factor's empirical relationship reflected these detectors' tendency to remain diffusion-limited during irradiation, which was previously established using Arrhenius-analysis of the post-irradiation, temperature-dependent dark current measurements on each. Collectively, the results affirmed the performance degradation stemmed from a reduction of the minority carrier recombination lifetime via generation of additional defects by proton-induced displacement damage. For comparing detector's radiation-tolerance, the results indicated that damage factors alone were not ideal, but their empirical relationships would serve as heuristics in this role.Index Terms-Damage factor, infrared detector, minority carrier lifetime, nBn, proton irradiation, unipolar barrier detector.

The radiation tolerance characterization of dual band InAs/GaSb type-II strain-layer superlattice pBp detectors of varying size using 63 MeV proton irradiation is presented. The detectors' mid-wave infrared performance degraded with increasing proton fluence ΦP up to 3.75 × 1012 cm−2 or, equivalently, a total ionizing dose = 500 kRad (Si). At this ΦP, an ∼31% drop in quantum efficiency η, ∼2 order increase in dark current density JD, and consequently, >1 order drop in calculated detectivity D* were observed. Proton damage factors were determined for η and D*. Arrhenius-analysis of temperature-dependent JD measurements reflected significant changes in the activation energies following irradiation.

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