The HyTI (Hyperspectral Thermal Imager) mission, funded by NASA’s Earth Science Technology Office InVEST (InSpace Validation of Earth Science Technologies) program, will demonstrate how high spectral and spatial long-wave infrared image data can be acquired from a 6U CubeSat platform. The mission will use a spatially modulated interferometric imaging technique to produce spectro-radiometrically calibrated image cubes, with 25 channels between 8-10.7 μm, at a ground sample distance of ~70 m. The HyTI performance model indicates narrow band NEΔTs of <0.3 K. The small form factor of HyTI is made possible via the use of a no-moving-parts Fabry-Perot interferometer, and JPL’s cryogenically-cooled HOT-BIRD FPA technology. Launch is scheduled for no earlier than October 2020. The value of HyTI to Earth scientists will be demonstrated via on-board processing of the raw instrument data to generate L1 and L2 products, with a focus on rapid delivery of data regarding volcanic degassing, land surface temperature, and precision agriculture metrics.
In this paper, we report our recent efforts in achieving high performance in Antimonides type-II superlattice (T2SL) based infrared photodetectors using the barrier infrared detector (BIRD) architecture, resonator pixel light coupling mechanism, and digital read out integrated circuits (DROICs).
The InAs/InAsSb (Gallium-free) type-II strained-layer superlattice (T2SLS) is an adjustable band gap, broad-band III-V infrared detector material that has emerged in recent years as an alternative to the more established InAs/GaSb type-II superlattice. We have reported results on a mid-wavelength focal plane array (FPA) based on the InAs/InAsSb T2SLS unipolar barrier infrared detector architecture. Significantly, the FPA exhibits very good operating characteristics at 160 K, demonstrating a considerably operating temperature advantage over the MWIR market-leading InSb FPAs, while maintaining III-V semiconductor manufacturing robustness. In this article we summarize the development at the NASA Jet Propulsion Laboratory leading to the mid-wavelength InAs/InAsSb T2SLS infrared detectors, provide a brief look at the history of the development of the InAs/InAsSb T2SLS absorber, and survey the current status of InAs/InAsSb T2SLS detectors.
Long-wavelength infrared (LWIR) focal plane arrays (FPAs) needed for Earth Science imaging, spectral imaging, and sounding applications have always been among the most challenging in infrared photodetector technology due to the rigorous material growth, device design and fabrication demands. Future small satellite missions will present even more challenges for LWIR FPAs, as operating temperature must be increased so that cooler (and radiator) volume, mass, and power can be reduced. To address this critical need, we are working on following three technologies. 1) Type-II superlattice (T2SL) barrier infrared detector (BIRD), which combines the high operability, spatial uniformity, temporal stability, scalability, producibility, and affordability advantages of the quantum well infrared photodetector (QWIP) FPA with the better quantum efficiency and dark current characteristics. A mid-wavelength infrared (MWIR) T2SL BIRD FPA is a key demonstration technology in the (6U) CubeSat Infrared Atmospheric Sounder (CIRAS) funded under the ESTO InVEST Program. A LWIR T2SL BIRD FPA is also being developed under the ESTO SLI-T Program for future thermal infrared (TIR) land imaging needs. 2) The resonator pixel technology, which uses nanophotonics light trapping techniques to achieve strong absorption in a small detector absorber volume, thereby enabling enhanced QE and/or reduced dark current. 3) High dynamic range 3D Readout IC (3DROIC), which integrates a digital reset counter with a conventional analog ROIC to provide a much higher effective well capacity than previously achievable. The resulting longer integration times are especially beneficial for high flux/dark current LWIR applications as they can improve signal-to-noise ratio and/or increase the operating temperature. By combining the aforementioned technologies, this project seeks to demonstrate a cost-effective, high-performance LWIR FPA technology with significantly higher operating temperature and sensitivity than previously attainable, and with the flexibility to meet a variety of Earth Science TIR measurement needs, particularly the special requirements of small satellite missions.
The unipolar barrier photodetector architecture such as the nBn provides an effective means for lowering generationrecombination dark current by suppressing Shockley-Read-Hall processes, and for reducing surface leakage dark current. This has been especially beneficial for III-V semiconductor based infrared photodiodes, which traditionally tend to suffer from excess depletion dark current and the lack of good surface passivation. Advances in bulk and type- II superlattice infrared absorber materials have provided continuously adjustable cutoff wavelength span ranging from 2 to 14 μm and beyond, greatly expanding the limited coverage provided by traditional bulk III-V infrared detectors based on InGaAs and InSb. In this work we discuss recent developments of antimonide-based extended-SWIR, MWIR, and LWIR detectors and focal plane arrays at the NASA Jet Propulsion Laboratory.
We provide a brief overview of recent progress in III-V semiconductor infrared photodetectors resulting from advances in infrared detector materials, including type-II superlattices (T2SL) and InAsSb alloy, and the unipolar detector architecture. We summarize T2SL unipolar barrier infrared detector and focal plane array development at the NASA Jet Propulsion Laboratory in support of the Vital Infrared Sensor Technology Acceleration (VISTA) Program. We also comment on the connection of T2SL barrier infrared detector to MCT infrared detectors.
Recently we have demonstrated a novel method of extending the cut-off wavelength of InAsSb nBn detectors, by incorporating a series of monolayers of InSb. Here we study photoluminescence and minority carrier lifetime of this InAsSb/InSb digital alloy. While increasing temperature from 15 K to 40 K we show a 14 meV blue shift of the photoluminescence peak energy and a decrease in lifetime. This deviation from the expected Varshni empirical relation indicates strong carrier localization. We contrast to photoluminescence and lifetime results in bulk InAsSb. We discuss implications of this localization for design of digital alloy InAsSb/InSb nBn detectors.
The depletion and surface leakage dark current suppression properties of unipolar barrier device architectures such as the nBn have been highly beneficial for III–V semiconductor-based infrared detectors. Using a one-dimensional drift-diffusion model, we theoretically examine the effects of contact doping, minority carrier lifetime, and absorber doping on the dark current characteristics of nBn detectors to explore some basic aspects of their operation. We found that in a properly designed nBn detector with highly doped excluding contacts the minority carriers are extracted to nonequilibrium levels under reverse bias in the same manner as the high operating temperature (HOT) detector structure. Longer absorber Shockley–Read–Hall (SRH) lifetimes result in lower diffusion and depletion dark currents. Higher absorber doping can also lead to lower diffusion and depletion dark currents, but the benefit should be weighted against the possibility of reduced diffusion length due to shortened SRH lifetime. We also briefly examined nBn structures with unintended minority carrier blocking barriers due to excessive n-doping in the unipolar electron barrier, or due to a positive valence band offset between the barrier and the absorber. Both types of hole blocking structures lead to higher turn-on bias, although barrier n-doping could help suppress depletion dark current.
We report our recent developments of antimonide based infrared photodetectors utilizing a complementary barrier infrared detector (CBIRD) design. The new generation of devices can operate close to zero bias with the same quantum efficiency as the initial design. 320x256 pixel long-wavelength infrared focal plane arrays utilizing optimized design have been demonstrated with 8.8 μm cutoff wavelength and noise equivalent differential temperature of 26 mK at operating temperature of 80 K for 300 K background and f/2 optics. As CBIRD detectors became valuable candidates for space-based instruments, question of their radiation tolerance became important. Here, we report our investigations of the proton irradiation effects on the photodetector performance.
III-V semiconductors offer a highly effective platform for the development of sophisticated heterostructure-based MWIR and LWIR detectors, as exemplified by the high-performance double heterstructure (DH) nBn, XBn, and type- II superlattice infrared detectors. A key enabling design element is the unipolar barrier, which is used to implement the complementary barrier infra-red detector (CBIRD) design for increasing the collection efficiency of photogenerated carriers, and reducing dark current generation without impeding photocurrent flow. Heterostructure superlattice detectors that make effective use of unipolar barriers have demonstrated strong reduction of generationrecombination (G-R) dark current due to Shockley-Read-Hall (SRH) processes. In the last several years we solely focused on the development of antimonide based IR detectors. Recently, we demonstrated RoA values over 14,000 Ohm cm2 for a 9.9 μm cutoff device by incorporating electron-blocking and hole-blocking unipolar barriers. This device has shown 300K BLIP operation with f/2 optics at 87 K with blackbody * of 1.1x1011 cm Hz1/2/W.
We examine carrier transport in unipolar barrier infrared photodetectors and discuss aspects of barrier, contact, and absorber properties that can affect minority carrier collection. In a barrier infrared detector the unipolar barrier should block only the majority carriers while allowing the un-impeded flow of the minority carriers. Under the right conditions, unipolar barrier doping can reduce generation-recombination dark current without affecting minority carrier extraction. In an nBn structure, ideally with an electron unipolar barrier, improper barrier doping or barrier-absorber valence band offset could also block minority carriers and result in higher turn-on bias. We also examined the temperature-dependent turn-on bias in an n+Bn device and showed that observed behavior may be attributed to contact doping. Hole mobility in n-doped type-II superlattice (T2SL) is believed to be very low because of the extremely large effective mass along the growth direction. In practice MWIR and LWIR barrier infrared detectors with n-type T2SL absorbers have demonstrated good optical response. A closer inspection of the T2SL band structure offers a possible explanation as to why the hole mobility may not be as poor as suggested by the simple effective mass picture.
In this work we investigate the high temperature performance of mid-wavelength infrared InAsSb-AlAsSb nBn detectors with cut-off wavelengths near 4.5μm. The quantum efficiency of these devices is 35% without antireflection coatings and does not change with temperature in the 77 - 325K temperature range, indicating potential for room temperature operation. The device dark current stays diffusion limited in the 150K-325K temperature range and becomes dominated by generation-recombination processes at lower temperatures. Detector detectivities of D*(λ) = 1x109 (cm Hz0.5/W) at T = 300K and D*(λ) = 5x109 (cm Hz0.5/W) at T = 250K, which is easily achievable with a one stage TE cooler.
We present an overview of III-V semiconductor-based infrared detector and focal plane array development at the NASA Jet Propulsion Laboratory in recent years. Topics discussed include: (1) the development of long-wavelength quantum well infrared photodetector for imaging spectrometer applications, (2) the concept and realization of the submonolayer quantum dot infrared photodetector (SML-QDIP) as an alternative to the standard QDIP-based on Stranski-Krastanov (SK) quantum dots, (3) the mid-wavelength infrared quantum dot barrier infrared detector with extended cutoff wavelength, and (4) high-performance type-II superlattice long-wavelength infrared detectors based on the complementary barrier infrared detector architecture.
In this study optical modulation response and photoluminescence spectroscopy were used to study mid-wave Ga-free
InAs/InAsSb superlattices. The minority carrier lifetimes in the different samples varied from 480 ns to 4700 ns, partly
due to different background doping concentrations. It was shown that the photoluminescence intensity can be used as a
fast non-destructive tool to predict the material quality. It was also demonstrated that it is crucial to use a low excitation
power in the photoluminescence measurements in order to get a good correlation between the photoluminescence
intensity and the minority carrier lifetime.
Modulation transfer function (MTF) is the ability of an imaging system to faithfully image a given object. The MTF of
an imaging system quantifies the ability of the system to resolve or transfer spatial frequencies. In this presentation we
will discuss the detail MTF measurements of 1024x1024 pixels multi-band quantum well infrared photodetector and
320x256 pixels long-wavelength InAs/GaSb superlattice infrared focal plane arrays.
Infrared focal plane arrays (FPAs) covering broad mid- and long-IR spectral ranges are the central parts of the
spectroscopic and imaging instruments in several Earth and planetary science missions. To be implemented in the space
instrument these FPAs need to be large-format, uniform, reproducible, low-cost, low 1/f noise, and radiation hard.
Quantum Well Infrared Photodetectors (QWIPs), which possess all needed characteristics, have a great potential for
implementation in the space instruments. However a standard QWIP has only a relatively narrow spectral coverage. A
multi-color QWIP, which is compromised of two or more detector stacks, can to be used to cover the broad spectral
range of interest. We will discuss our recent work on development of multi-color QWIP for Hyperspectral Thermal
Emission Spectrometer instruments. We developed QWIP compromising of two stacks centered at 9 and 10.5 μm, and
featuring 9 grating regions optimized to maximize the responsivity in the individual subbands across the 7.5-12 μm
spectral range. The demonstrated 1024x1024 QWIP FPA exhibited excellent performance with operability exceeding
99% and noise equivalent differential temperature of less than 15 mK across the entire 7.5-12 μm spectral range.