Search

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]

While the n-type InAs/InAsSb type-II strained layer superlattice (T2SLS) has demonstrated excellent detector and focal plane array performance in the mid-wavelength infrared, it is limited in its attainable quantum efficiency (QE) in the long and very long wavelength infrared due to short hole diffusion length and modest absorption coefficient. We explore InAs/InAsSb T2SLS unipolar barrier infrared detectors that contain p-type absorber layers in order to take advantage of the longer electron diffusion length for QE enhancement. We find that while they can achieve enhanced QE, their dark current characteristics are affected by the presence of metallurgical and surface p-n junctions, and are best operated under lower biasing conditions where the tunneling dark currents are less pronounced. We report results on complementary barrier infrared detector structures that use n-type absorbers, a combination of p- and n-type absorbers, and p-type absorbers, with cutoff wavelengths ranging from 10.0 µm to 15.3 µm. [ABSTRACT FROM AUTHOR]

We studied long and very long wavelength InAs/InAsSb superlattice barrier infrared detectors that contain p-type absorber layers in order to take advantage of the longer electron diffusion length for quantum efficiency (QE) enhancement. While they can achieve higher QE than devices that use only n-type absorbers, their dark current characteristics are affected by the presence of metallurgical and surface p–n junctions, and are best operated under lower biasing conditions where the tunneling dark currents are less pronounced. Rather than using a p-type absorber only, a barrier infrared detector structure with a combination of p- and n-type absorber sections can benefit from a shallower mesa etch that reduces fabrication demands and also decreases the p-type absorber exposed surface area. We compare four complementary barrier infrared detector structures that use an n-type absorber, a combination of p- and n-type absorbers, or a p-type absorber and briefly report results from a 13.3 μm cutoff focal plane array. [ABSTRACT FROM AUTHOR]

InAs/InAsSb type-II superlattice focal plane arrays that demonstrate high operability and uniformity with cutoffs ranging from 5 μm to 13 μm have already been demonstrated. Compared to InAs/GaSb, the InAs/InAsSb superlattice is easier to grow and has longer minority carrier lifetimes, but requires a longer superlattice period to achieve long or very long wavelength cutoffs. A longer type-II superlattice period leads to smaller absorption coefficients and larger growth-direction hole conductivity effective masses. We explore by theoretical modeling some of the ideas aimed at addressing these challenges for the long and very long wavelength InAs/InAsSb superlattice. Increasing the Sb fraction in the InAsSb alloy can reduce the InAs/InAsSb superlattice period significantly, but this benefit can be negated by Sb segregation. Thin AlAsSb barrier layers can be inserted in InAs/InAsSb to form polytype W, M, and N superlattices in order to increase electron–hole wavefunction overlap for stronger optical absorption. However, this strategy can be unfavorable since the AlAsSb barriers increase the band gap, and thereby increase the superlattice period required to reach a given cutoff wavelength. Metamorphic growth on virtual substrates with larger lattice constants than GaSb can decrease the superlattice period needed to reach a specified cutoff wavelength, but this benefit should be weighed against the need for metamorphic buffer growth and the resulting higher defect density. [ABSTRACT FROM AUTHOR]

There was a significant improvement in the performance of infrared nBn detectors utilizing InAs/InAsSb absorbers culminating in the development of infrared focal plane arrays (FPAs) with excellent operability (99.7%) and operating at temperature significantly higher than InSb FPAs. In this work, we demonstrated that these detectors can operate with very low dark current densities enabling their use in applications with a low-to-medium level of background illumination. We showed that single pixel photodetectors with a cut-off wavelength of 4.8 μm and a quantum efficiency of QEmax = 35% under backside-illumination have a dark current density of 1 × 10−10 A/cm2 at an operating bias of −0.1 V and temperature T = 100 K. Additionally, we compared the single pixel dark current results with measurements of the dark current in FPAs. The FPA showed excellent performance with an operability of 99.7% and was able to reach a mode dark current density of 5 × 10−11 A/cm2 at 80 K. [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]

Optical components based on metasurfaces (metalenses) offer an alternative methodology for microlens arrays. In particular, metalens arrays have the potential of being monolithically integrated with infrared focal plane arrays (IR FPAs) to increase the operating temperature and sensitivity of the latter. In this work, we demonstrate a type of transmissive metalens that focuses the incident light (λ = 3–5 μm) on the detector plane after propagating through the substrate, i.e., solid-immersion type of focusing. The metalens is fabricated by etching the backside of the detector substrate material (GaSb here), making this approach compatible with the architecture of back-illuminated FPAs. In addition, our designs work for all incident polarizations. We fabricate a 10 × 10 metalens array that proves the scalability of this approach for FPAs. In the future, these solid-immersion metalenses arrays will be monolithically integrated with IR FPAs. [ABSTRACT FROM AUTHOR]

• Long wavelength infrared (LWIR) InAs/InAsSb superlattice focal plane arrays (FPAs) for NASA land imaging applications. • Complementary barrier infrared detector (CBIRD) with p-type superlattice absorber for enhanced LWIR quantum efficiency. • CBIRD FPAs fabricated by conventional and by silicon-on-silicon processes both demonstrated good operability and uniformity. We explore InAs/InAsSb type-II superlattice long wavelength infrared detector based focal plane arrays for potential NASA land imaging applications. We used the complementary barrier infrared detector (CBIRD) architecture with p-type superlattice absorber (p-CBIRD), and with a combination of p-type and n-type superlattice absorbers (pn-CBIRD). CBIRD focal plane arrays fabricated using a conventional process and with an alternative silicon-on-silicon process have both demonstrated good operability and uniformity. [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]

The InAs/InAsSb (Gallium-free) type-II strained-layer superlattice (T2SLS) has emerged in the last decade as a viable infrared detector material with a continuously adjustable band gap capable of accommodating detector cutoff wavelengths ranging from 4 to 15 µm and beyond. When coupled with the unipolar barrier infrared detector architecture, the InAs/InAsSb T2SLS mid-wavelength infrared (MWIR) focal plane array (FPA) has demonstrated a significantly higher operating temperature than InSb FPA, a major incumbent technology. In this brief review paper, we describe the emergence of the InAs/InAsSb T2SLS infrared photodetector technology, point out its advantages and disadvantages, and survey its recent 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]