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The hyperspectral thermal imaging instrument for technology demonstration funded by NASA's Earth Science Technology Office under the In-Space Validation of Earth Science Technologies program requires focal plane array with reasonably good performance at a low cost. The instrument is designed to fit in a 6U CubeSat platform for a low-Earth orbit. It will collect data on hydrological parameters and Earth surface temperature for agricultural remote sensing. The long wavelength infrared type-II strain layer superlattices barrier infrared detector focal plane array is chosen for this mission. With the driving requirement dictated by the power consumption of the cryocooler and signal-noise-ratio, cut-off wavelengths and dark current are utilized to model instrument operating temperature. Many focal plane arrays are fabricated and characterised, and the best performing focal plane array that fulfils the requirements is selected. The spectral band, dark current and 8-9.4 μm pass band quantum efficiency of the candidate focal plane array are: 8-10.7 μm, 2.1·10-5 A/cm², and 47%, respectively. The corresponding noise equivalent difference temperature and operability are 30 mK and 99.7%, respectively. Anti-reflective coating is deposited on the focal plane array surface to enhance the quantum efficiency and to reduce the interference pattern due to an absorption layer parallel surfaces cladding material. [ABSTRACT FROM AUTHOR]

Mid-wavelength infrared detectors and focal plane array based on n-type InAs/InAsSb type-II strained layer superlattice absorbers have achieved excellent performance. In the long and very long wavelength infrared, however, n-type InAs/InAsSb type-II strained layer superlattice detectors are limited by their relatively small absorption coefficients and short growth-direction hole diffusion lengths, and consequently have only been able to achieve modest level of quantum efficiency. The authors present an overview of their progress in exploring complementary barrier infrared detectors that contain p-type InAs/InAsSb type-II strained layer superlattice absorbers for quantum efficiency enhancement. The authors describe some representative results, and also provide additional references for more indepth discussions. Results on InAs/InAsSb type-II strained layer superlattice focal plane arrays for potential NASA applications are also briefly discussed. [ABSTRACT FROM AUTHOR]

InAs/InAsSb type-II strained layer superlattice high-operating temperature barrier infrared detector (HOT-BIRD) focal plane arrays (FPAs) were fabricated for mid-wavelength infrared hyperspectral imaging applications on the CubeSat Infrared Atmospheric Sounder (CIRAS). At 115 K, a $5.4 ~\mu \text{m}$ cutoff FPA demonstrated a mean quantum efficiency of 53% in the 3- $5 ~\mu \text{m}$ band, and a mean dark current density of $1.7\,\,\times10$ −7 A/cm2. The mean noise equivalent differential temperature (NEDT) is 22.9 mK for 300 K background and f/7.8 optics, with an NEDT operability of 99.94%. The FPA meets the hyperspectral imaging requirements of CIRAS. [ABSTRACT FROM AUTHOR]

In the past decade, infrared detectors with InAs/InAsSb (Gallium-free) type-II strained layer superlattice absorbers became a technology of interest for many imaging applications. In this work, we study the dependence of minority carrier (hole) transport, absorption coefficient, and quantum efficiency (QE) of a 5.6 μm cutoff wavelength mid-wavelength infrared InAs/InAsSb detector on temperatures and applied bias. We found that the minority carrier lifetime is very long (τ ≈ 5.5 μs) and is temperature independent in the temperature range T = 50–150 K. The back-side illuminated QE without anti-reflection coating increases from ∼30% at T = 50 K to ∼60% at T = 180 K. The minority carrier (hole) diffusion length, Ldh, was found from QE and absorption coefficient. The hole diffusion length at T = 50 K is Ldh = 2.4 μm and increases monotonically to Ldh = 7.2 μm at T = 180 K. The hole mobility, calculated from diffusion length and minority carrier lifetime, is μh = 4.5 cm2/V s at T = 50 K and increases with temperature to reach μh = 7.2 cm2/V s at T = 150 K. In addition, we find that at lower temperatures where the diffusion length is shorter, the stronger QE dependence on applied bias is due to minority carrier collection from the depletion region, whose width increases with applied bias. [ABSTRACT FROM AUTHOR]

Highlights • Theoretical analysis provides simple comparisons of bulk and type-II superlattice infrared absorbers. • Covering short-wavelength infrared to very long wavelength infrared. • Type-II superlattice mid-wavelength infrared detector and focal plane array out-performs InSb. Abstract Advances in bulk III-V semiconductor material such as InGaAsSb and metamorphic InAsSb, as well as in a variety of type-II superlattices such as InGaAs/GaAsSb, InAs/GaSb, and InAs/InAsSb, have provided continuously adjustable cutoff wavelength coverage from the short to the very long wavelength infrared. We perform basic theoretical analysis to provide comparisons of different infrared materials. We also briefly report experimental results on a mid-wavelength InAs/InAsSb type-II superlattice unipolar barrier infrared detector and a focal plane array with significantly higher operating temperature than InSb. [ABSTRACT FROM AUTHOR]

We report focal plane array (FPA) results on a mid-wavelength InAs/InAsSb type-II strained layer superlattice (T2SLS) unipolar barrier infrared detector with a cutoff wavelength of 5.4 μm. For 300 K background in the 3–5-μm band, f/2 aperture, an FPA operating at 150 K exhibits a mean noise equivalent differential temperature (NEDT) of 18.5 mK, and an NEDT operability of 99.7%. The NEΔT distribution has a width of 8 mK, with no noticeable distribution tail, indicating excellent uniformity. The mean noise-equivalent irradiance is 9.1 × 1011 photons/sec-cm2. The mean quantum efficiency is 49.1% without antireflection coating, and the mean specific detectivity (D*) is 2.53 × 1011 cm-Hz½/W. Benefitting from an absorber material with a much longer Shockley–Read–Hall minority carrier lifetime, and a device architecture that suppresses generation-recombination and surface-leakage dark current, the InAs/InAsSb T2SLS barrier infrared detector FPA has demonstrated a significantly higher operating temperature than the mid-wavelength infrared market-leading InSb. [ABSTRACT FROM AUTHOR]

We analyze and compare different aspects of InAs/InAsSb and InAs/GaSb type-II superlattices for infrared detector applications and argue that the former is the most effective when implemented for mid-wavelength infrared detectors. We then report results on an InAs/InAsSb superlattice based mid-wavelength high operating temperature barrier infrared detector. At 150 K, the 50% cutoff wavelength is 5.37 μm, the quantum efficiency at 4.5 μm is ∼52% without anti-reflection coating, the dark current density under −0.2 V bias is 4.5 × 10−5 A/cm2, and the dark-current-limited and the f/2 black-body (300 K background in 3–5 μm band) specific detectivities are 4.6 × 1011 and 3.0 × 1011 cm-Hz1/2/W, respectively. A focal plane array made from the same material exhibits a mean noise equivalent differential temperature of 18.7 mK at 160 K operating temperature with an f/2 optics and a 300 K background, demonstrating significantly higher operating temperature than InSb. [ABSTRACT FROM AUTHOR]

A long wavelength infrared (LWIR) type-II superlattice (T2SL) is typically characterized by a very large valence-band-edge curvature effective mass, which is often assumed to lead to poor hole mobility. A detailed examination of the LWIR T2SL heavy-hole 1 (hh1) band structure reveals that a hole with non-zero in-plane momentum ( k ‖ ≠ 0 ) can move with a much larger group velocity component along the growth direction than one at the band edge ( k ‖ = 0 ), and that the hh1 miniband width can exhibit a very strong dependence on the in-plane wavevector k ‖ . To distill the band structure effects relevant to hole transport into a simple quantity, we describe a formulation for computing the thermally averaged conductivity effective mass. We show that the LWIR T2SL hole conductivity effective masses along the growth direction can be orders of magnitude smaller than the corresponding band-edge curvature effective masses. We compare the conductivities effective masses of InAs/GaSb T2SL and InAs/InAsSb T2SL grown pseudomorphically on GaSb substrate, as well as the metamorphic bulk InAsSb and InAs/InAsSb T2SL. [ABSTRACT FROM AUTHOR]

Abstract: The InAs/GaSb type-II superlattice based complementary barrier infrared detector (CBIRD) has already demonstrated very good performance in long-wavelength infrared (LWIR) detection. In this work, we describe results on a modified CBIRD device that incorporates a double tunnel junction contact designed for robust device and focal plane array processing. The new device also exhibited reduced turn-on voltage. We also report results on the quantum dot barrier infrared detector (QD-BIRD). By incorporating self-assembled InSb quantum dots into the InAsSb absorber of the standard nBn detector structure, the QD-BIRD extend the detector cutoff wavelength from ∼4.2μm to 6μm, allowing the coverage of the mid-wavelength infrared (MWIR) transmission window. The device has been observed to show infrared response at 225K. [Copyright &y& Elsevier]

Abstract: The nearly lattice-matched InAs/GaSb/AlSb (antimonide) material system offers tremendous flexibility in realizing high-performance infrared detectors. Antimonide-based superlattice infrared absorbers can be customized to have cutoff wavelengths ranging from the short-wave infrared (SWIR) to the very long-wave infrared (VLWIR). They can be used in constructing sophisticated heterostructures to enable advanced infrared photodetector designs. In particular, they facilitate the construction of unipolar barriers, which can block one carrier type but allow the un-impeded flow of the other. Unipolar barriers are used to implement the barrier infrared detector (BIRD) design for increasing the collection efficiency of photo-generated carriers, and reducing dark current generation without impeding photocurrent flow. We report our recent efforts in achieving state-of-the-art performance in antimonide superlattice based long-wavelength infrared photodetectors using a complementary barrier infrared detector (CBIRD) design. [Copyright &y& Elsevier]

Abstract: A limitation to the advancement of the strained-layer superlattice technology for infrared detection is unwanted high dark currents and low R 0 A values, especially at long-wavelengths. In this paper, we discuss dark current characteristics of LWIR InAs/GaSb type-II superlattice detectors. Comparing devices with different dominant mechanisms, a more thorough analysis at low temperatures is provided. [Copyright &y& Elsevier]

We report on the details of inductively coupled plasma etching for achieving low dark current long-wavelength infrared focal plane arrays (FPAs). External factors that influence the etching process are studied. A high-quality hard mask for excellent pattern transfer is discussed. Next, a suitable mounting technique for good thermal contact is described. Finally, the challenges and differences between etching large 200-\mum test diodes and small 28-\mum FPA pixels are discussed. The complete etching process is then demonstrated on a 320\,\times\,256 complementary barrier infrared detector FPA. The mean dark current density of 2.2\,\times 10^-4~A/cm^2 is measured at an operating bias of 128 mV with a 50% cutoff wavelength of 8.8 \mum. Good imagery is achieved with an array yielding an 81% fill factor with 97% operability. Operating at T=80~K, the measured mean noise equivalent differential temperature is 18.6 mK, and the mean detectivity is D^\ast=1.3\times 10^11~cm\-Hz^1/2/W. [ABSTRACT FROM PUBLISHER]

Surface leakage reduction has been achieved using BCl3/Cl2/CH4/H2/Ar inductively coupled plasma dry etching for pixel isolation of high performance long-wave infrared superlattice detectors. The leakage has been minimized by effectively increasing the surface resistivity by more than 7.4 times and decreasing the surface state density by more than 3.8 times. Through altering the etch mechanism, the dark current density was reduced by more than two orders of magnitude where a dark current of 1.01×10-5 A/cm2 at 200 mV was achieved at T=77 K for a 10.3 μm detector with a peak quantum efficiency value of 30% (without antireflection coating). [ABSTRACT FROM AUTHOR]

The authors report on growth, material characterization, and device performance of infrared photodetectors based on type II InAs/GaSb superlattices using the complementary barrier infrared detector (CBIRD) design. In this paper, control steps for improvement of material quality in terms of surface, structural, and optical properties of infrared detectors grown at Jet Propulsion Laboratory are described. For a specific CBIRD studied, these quality control steps indicate high structural and optical quality of the grown material. Furthermore, single-element detector from the optimized growth conditions exhibit dark current density less than 1 × 10-5 A/cm2 at applied biases up to Vb = 0.36 V (T = 77 K), so this material can be utilized for focal plane arrays development. [ABSTRACT FROM AUTHOR]

Highlights • MTF measurement on type II SLS. • Projection MTF versus one-to-one MTF. • With and without Lens MTF correction. • Diffusion length estimate from MTF. • Lifetime estimate using diffusion length. Abstract Mid-wavelength Infrared (MWIR) and long-wavelength infrared (LWIR) Barrier Infrared Detector (BIRD) based on Antimonides Type-II superlattice detector array material are hybridized to 640 × 512, 1024 × 1024 and 1344 × 784 pixels format read out integrated circuits. The focal plane arrays (FPAs) Noise Equivalent Temperature Difference (NEΔT), Quantum Efficiency (η), Dark Current Density (J D), and Modulation Transfer Function (MTF) performance were measured at operating temperatures. High performance 640 × 512 array format MWIR High Operating Temperature (HOT) FPA has typical NEΔT ∼ 19 mK, J D ∼ 6.2 × 10−7 A/cm2, and η ∼ 53% using 3–5 μm band pass filter at 115 K operating temperatures. Best performance 640 × 512 array format LWIR FPA has NEΔT ∼ 25 mK, J D ∼ 2.5 × 10−5 A/cm2 and η ∼ 41% using 8–9.4 μm band pass filter at 60 K operating temperatures. For MTF investigation, a novel direct one-to-one image approach of Line Spread Function (LSF) and Edge Spread Function (ESF) are patterned onto substrate-removed FPAs. The direct LSF and ESF image are produced by 1000 A° thick gold layer deposition. The direct image horizontal and vertical MTFs are compared with projected knife-edge ESF-derived MTFs and results indicate that direct image MTFs have higher values compared to projected knife-edge ESF-derived MTFs at a Nyquist frequency. However, direct image MTF requires no lens MTF correction. The only relevant requirement for the direct image MTF is for the deposited pattern and substrate to be extremely thinned in which the HOT-BIRD FPAs fulfilled for this investigation. [ABSTRACT FROM AUTHOR]

Abstract: We report growth, processing, and characterization of antimonide superlattice long-wavelength infrared photodetectors based on the complementary barrier infrared detector (CBIRD) design. We used photoluminescence measurements for evaluating detector material and studied the influence of the material quality on the intensity of the photoluminescence. We performed direct noise measurements of the superlattice detectors and demonstrated that while intrinsic 1/f noise is absent in superlattice heterodiode, side-wall leakage current can become a source of strong frequency-dependent noise. We developed an effective dry etching process for these complex antimonide-based superlattices that enabled us to fabricate single pixel devices as well as large format focal plane arrays. [Copyright &y& Elsevier]