In this presentation, I’ll discuss the infusion of high operating temperature mid-wave and long-wave BIRD technology in to a myriad Earth and space science applications such as Hyperspectral Thermal Imager (HyTI), HyTI-2, Hyperspectral Thermal Emission Spectrometer (HyTES), compact – Fire Irradiance Spectral Tracker (c-FIRST), Sustainable Land Imaging (SLI), and non-saturating, simultaneous multiband, infrared imager for Io and Venus applications.
Based on the recent success of our strained-layer superlattice (SLS)-based infrared (IR) camera that performed Earth imaging from the International Space Station (ISS) in 2019 we have built, what we consider, to be the next generation multi-band SLS imaging system. The Compact Thermal Imager (CTI) was installed on the Robotic Refueling Mission 3 (RRM3) and attached to the exterior of the ISS. From this location we were able to capture 15 million images of a multitude of fires around the globe in 2019. This unexpected trove of data initiated quite a bit of scientific interest to further utilize this imaging capability but would include features to more precisely monitor terrestrial fires and other surface phenomena. To this end, we developed a technique to install specific bandpass filters directly onto the SLS detector hybrid assembly. Utilizing this technique we have built a CTI-2 camera system with two filters, 4 and 11μm, and have made a second detector assembly with six filter bands from 4- 12μm. This second system will also be used to supplement Landsat remote imaging monitoring approximate land surface temperatures, monitor evapotranspiration, sea ice and glacier dynamics. The CTI-2 camera is based on a 1,024x1,024 (1kx1k) format SLS detector hybridized to a FLIR ISC0404 readout integrated circuit (ROIC). The six band SLS focal plane array is based on the 640x512 FLIR ISC 9803 ROIC. This camera system is based on the Landsat 8 and 9 Thermal IR Sensors (TIRS) instrument and one of its purposes is to perform ground truthing for the Landsat 8/9 data at higher spectral resolution. Both Landsat TIRS instruments are dual band thermal IR sensors centered on 11 and 12μm (each with about a 1μm bandpass). Both of our SLS systems utilize a Ricor K548 cryocooler. To streamline costs and development time we used commercial optics and both commercial and custom NASA electronic components. A primary feature of these camera systems is the incorporation of specific filters to collect fire data at ~3.9μm and thermal data at ~11μm. The CTI- 2 instrument is designed for 37 m /pixel spatial resolution from 410km orbit (ISS orbit). In this paper, we will present the design and performance of the focal plane, optics, electronics and mechanical structure of the dual-band CTI-2 and the focal plane performance of the six-band focal plane.
In 1988 DARPA provided funding to NASA’s Goddard Space Flight Center to support the development of GaAs Quantum Well Infrared Photodetectors (QWIP). The goal was to make a single element photodetector that might be expandable to a two-dimensional array format. Ultimately, this led to the development of a 128 x 128 element array in collaboration with AT&T Bell Labs and Rockwell Science Center in 1990. We continued to develop numerous generations of QWIP arrays most recently resulting in the multi-QWIP focal plane for the NASA-US Geological Survey (USGS) Landsat 8 mission launched in 2013 and a similar instrument on the Landsat 9 mission to be launched in 2020. Toward the end of the Landsat 8 QWIP-based Thermal Infrared Sensor (TIRS) instrument the potential of the newly developed Strained Layer Superlattice (SLS) detector array technology became of great interest to NASA for three primary reasons: 1) higher operating temperature; 2) broad spectral response and; 3) higher sensitivity. We have collaborated extensively with QmagiQ, LLC and Northwestern University to further pursue and advance the SLS technology ever since we started back in 2012. In December of 2018 we launched the first SLS-based IR camera system to the International Space Station on board the Robotic Refueling Mission #3 (RRM3). This paper will describe the evolution of QWIP technology leading to the current development of SLS-based imaging systems at the Goddard Space Flight Center over the past 30 years.
GaSb-based infrared (IR) photodetector technology progression is toward larger-format focal plane arrays (FPAs). This requires a performance-based and cost-based manufacturing process on larger diameter substrates for improved throughput, volume, and yield. IQE has demonstrated molecular beam epitaxy (MBE) growth processes for barrier-design detectors (nBn) in multi-wafer configurations on 4-inch and 5-inch diameter GaSb substrates, and via a metamorphic process on 4-inch and 6-inch GaAs substrates. Recently we took the next step in this progression, growing nBn detectors on 6-inch Si substrates coated with CVD-grown Ge, opening the door for potential integration with Si-based electronic circuitry. Here, we compare the epiwafer characteristics (morphology, x-ray, PL) and diode performance (turn-on, QE, cutoff wavelength) of this M-nBn on Ge-Si with the same M-nBn on GaAs and the corresponding nBn structure grown on native GaSb substrate. Similar performance was obtained on all three types of substrates. We also present FPA data based on a 640×512 pixel, 15 μm pitch process without substrate removal, where QE ~ 80%, NE▵T < 20 mK, and operability <99% was demonstrated. The results represent an important technological path toward next-generation large-format IR detector array applications.
An infrared sensor technology that has made quick progress in recent years is the photodiode based on Type-II
InAs/(In)GaSb strained layer superlattices (SLS). We have developed Focal Plane Arrays (FPAs) with up to a million
pixels, quantum efficiency exceeding 50%, and cutoff wavelength ~ 10 microns. SLS offers the promise of the high
quantum efficiency and operating temperature of longwave infrared mercury cadmium telluride (MCT) at the price point
of midwave infrared indium antimonide (InSb). That promise is rapidly being fulfilled. This paper presents the current
state-of-the-art of this sensor technology at this critical stage of its evolution.
In the last few years infrared focal plane arrays based on Type-I GaAs/AlGaAs quantum well infrared photodetectors
(QWIPs) have been commercialized, providing excellent cost-effective imaging for security and surveillance and gas
imaging applications. A second cooled infrared sensor technology that has made significant advances in recent years is
photodiodes based on Type-II InAs/(In)GaSb strained layer superlattices (SLS). Imaging chips with upto a million
pixels, quantum efficiency exceeding 50%, and cutoff wavelength exceeding 10 microns have been recently
demonstrated. SLS offers the promise of the high quantum efficiency and operating temperature of longwave infrared
mercury cadmium telluride (MCT) at the price point of QWIP and midwave infrared indium antimonide (InSb). That
promise is rapidly being fulfilled. This paper presents the current state-of-the-art of both these sensor technologies at
this critical stage of their evolution.
The focal plane assembly for the Thermal Infrared Sensor (TIRS) instrument on NASA's Landsat Data Continuity
Mission (LDCM) consists of three 512 x 640 GaAs Quantum Well Infrared Photodetector (QWIP) arrays. The three
arrays are precisely mounted and aligned on a silicon carrier substrate to provide a continuous viewing swath of 1850
pixels in two spectral bands defined by filters placed in close proximity to the detector surfaces. The QWIP arrays are
hybridized to Indigo ISC9803 readout integrated circuits (ROICs). QWIP arrays were evaluated from four laboratories;
QmagiQ, (Nashua, NH), Army Research Laboratory, (Adelphi, MD), NASA/ Goddard Space Flight Center, (Greenbelt,
MD) and Thales, (Palaiseau, France). All were found to be suitable. The final discriminating parameter was the spectral
uniformity of individual pixels relative to each other. The performance of the QWIP arrays and the fully assembled,
NASA flight-qualified, focal plane assembly will be reviewed. An overview of the focal plane assembly including the
construction and test requirements of the focal plane will also be described.
We present the performance of longwave infrared focal plane arrays (FPAs) made from Type-II InAs/GaSb strained
layer superlattice (SLS) photodiodes. In 320x256 FPAs operating at 77K, we measure cutoff wavelength ~ 8.5 μm, dark
current density ~ 10-5 A/cm2, quantum efficiency > 5% (with 2 μm -thick absorber photodiode), and pixel operability ~
96%. Device physics and FPA performance are graphed. Current challenges are discussed.
The Thermal Infrared Sensor (TIRS) is a QWIP based instrument intended to supplement the Operational Land Imager
(OLI) for the Landsat Data Continuity Mission (LDCM) [1]. The TIRS instrument is a dual channel far infrared imager
with the two bands centered at 10.8μm and 12.0μm. The focal plane assembly (FPA) consists of three 640x512 GaAs
Quantum Well Infrared Photodetector (QWIP) arrays precisely mounted to a silicon carrier substrate that is mounted on
an invar baseplate. The two spectral bands are defined by bandpass filters mounted in close proximity to the detector
surfaces. The focal plane operating temperature is 43K. The QWIP arrays are hybridized to Indigo ISC9803 readout
integrated circuits (ROICs). Two varieties of QWIP detector arrays are being developed for this project, a corrugated
surface structure QWIP and a grating surface structure QWIP. This paper will describe the TIRS system noise
equivalent temperature difference sensitivity as it affects the QWIP focal plane performance requirements: spectral
response, dark current, conversion efficiency, read noise, temperature stability, pixel uniformity, optical crosstalk and
pixel yield. Additional mechanical constraints as well as qualification through Technology Readiness Level 6 (TRL 6)
will also be discussed.
KEYWORDS: Medium wave, Cameras, Temperature metrology, Black bodies, Aluminum, Staring arrays, Quantum well infrared photodetectors, Tantalum, Detection and tracking algorithms, Infrared radiation
The infrared photon flux emitted by an object depends not only on its temperature but also on a
proportionality factor referred to as its emissivity. Since the latter parameter is usually not known
quantitatively a priori, any temperature determination based on single-band radiometric
measurements suffers from an inherent uncertainty. Recording photon fluxes in two separate
spectral bands can in principle circumvent this limitation. The technique amounts to solving a
system of two equations in two unknowns, namely, temperature and emissivity. The temperature
derived in this manner can be considered absolute in the sense that it is independent of the
emissivity, as long as that emissivity is the same in both bands. QmagiQ has previously
developed a 320x256 midwave/longwave staring focal plane array which has been packaged into
a dual-band laboratory camera. The camera in question constitutes a natural tool to generate
simultaneous and independent emissivity maps and temperature maps of entire two-dimensional
scenes, rather than at a single point on an object of interest. We describe a series of measurements
we have performed on a variety of targets of different emissivities and temperatures. We examine
various factors that affect the accuracy of the technique. They include the influence of the
ambient radiation reflected off the target, which must be properly accounted for and subtracted
from the collected signal in order to lead to the true target temperature. We also quantify the
consequences of spectrally varying emissivities.
The development of type-II InAs/(In,Ga)Sb superlattice (SL) detectors with nBn design for single-color and
dual-color operation in MWIR and LWIR spectral regions are discussed. First, a 320 x 256 focal plane array (FPA) with
cutoff wavelength of 4.2 μm at 77K with average value of dark current density equal to 1 x 10-7 A/cm2 at Vb=0.7V (77
K) is reported. FPA reveals NEDT values of 23.8 mK for 16.3 ms integration time and f/4 optics. At 77K, the peak
responsivity and detectivity of FPA are estimated, respectively, to be 1.5 A/W and 6.4 x 1011 Jones, at 4 μm. Next,
implementation of the nBn concept on design of SL LWIR detectors is presented. The fabrication of single element nBn
based long wave infrared (LWIR ) with λc ~ 8.0 μm at Vb = +0.9 V and T = 100K detectors are reported. The bias
dependent polarity can be exploited to obtain two color response (λc1 ~ 3.5 μm and λc2 ~ 8.0 μm) under different polarity
of applied bias. The design and fabrication of this two color detector is presented. The dual band response (λc1 ~ 4.5 μm
and λc2 ~ 8 μm) is achieved by changing the polarity of applied bias. The spectral response cutoff wavelength shifts
from MWIR to LWIR when the applied bias voltage varies within a very small bias range (~100 mV).
In our research group, we develop novel dots-in-a-well (DWELL) photodetectors that are a hybrid of the quantum dot
infrared photodetector (QDIP). The DWELL detector consists of an active region composed of InAs quantum dots
embedded in InGaAs quantum wells. By adjusting the InGaAs well thickness, our structure allows for the manipulation
of the operating wavelength and the nature of the transitions (bound-to-bound, bound-to-quasibound and bound-to-continuum)
of the detector. Based on these principles, DWELL samples were grown using molecular beam epitaxy and
fabricated into 320 x 256 focal plane arrays (FPAs) with Indium bumps using standard lithography at the University of
New Mexico. The FPA evaluated was hybridized to an Indigo 9705 readout integrated circuit (ROIC) in collaboration
with QmagiQ LLC and tested with a CamIRaTM system manufactured by SE-IR Corp. From this evaluation, we report
the first two-color, co-located quantum dot based imaging system that can be used to take multicolor images using a
single FPA. We demonstrated that we can operate the device at an intermediate bias (Vb=-1.25 V) and obtain two color
response from the FPA at 77K. Using filter lenses, both MWIR and LWIR responses were obtained from the array at the
same bias voltage. The MWIR and LWIR responses are thought to be from bound states in the dot to higher and lower
lying states in the quantum well respectively. Temporal NEDT for the DWELL FPA was measured to be 80mK at 77K.
QmagiQ LLC, has recently completed building and testing high operability two-color Quantum Well Infrared Photodetector (QWIP) focal plane arrays (FPAs). The 320 x 256 format dual-band FPAs feature 40-micron pixels of spatially registered QWIP detectors based on III-V materials. The vertically stacked detectors in this specific midwave/longwave (MW/LW) design are tuned to absorb in the respective 4-5 and 8-9 micron spectral ranges. The ISC0006 Readout Integrated Circuit (ROIC) developed by FLIR Systems Inc. and used in these FPAs features direct injection (DI) input circuitry for high charge storage with each unit cell containing dual integration capacitors, allowing simultaneous scene sampling and readout for the two distinct wavelength bands. Initial FPAs feature pixel operabilities better than 99%. Focal plane array test results and sample images will be presented.
Room-temperature targets are detected at the furthest distance by imaging them in the long wavelength (LW: 8-12 μm) infrared spectral band where they glow brightest. Focal plane arrays (FPAs) based on quantum well infrared photodetectors (QWIPs) have sensitivity, noise, and cost metrics that have enabled them to become the best commercial solution for certain security and surveillance applications. Recently, QWIP technology has advanced to provide pixelregistered dual-band imaging in both the midwave (MW: 3-5 μm) and longwave infrared spectral bands in a single chip. This elegant technology affords a degree of target discrimination as well as the ability to maximize detection range for hot targets (e.g. missile plumes) by imaging in the midwave and for room-temperature targets (e.g. humans, trucks) by imaging in the longwave with one simple camera. Detection-range calculations are illustrated and FPA performance is presented.
We summarize the current state of 2-color Quantum Well Infrared Photodetector (QWIP) Focal Plane Array (FPA) technology. Our 2-color FPA architecture features 3 bumps/pixel to permit two vertically-stacked QWIPs to be separately biased and the two photocurrents to be simultaneously integrated. Pixel-registered imagery is simultaneously obtained in two spectral bands. We have successfully applied this architecture to realize 2-color FPAs in three sperate formats: LW/LW, MW/LW, and MW/MW. Fabrication and performance details are presented.
We report on the results of laboratory and field tests on a pixel-registered, 2-color MWIR/LWIR 256 X 256 QWIP FPA with simultaneous integrating capability. The FPA studied contained stacked QWIP structures with spectral peaks at 5.1 micrometer and 9.0 micrometer. Normally incident radiation was coupled into the devices using a diffraction grating designed to operate in both spectral bands. Each pixel is connected to the read-out integrated circuit by three bumps to permit the application of separate bias levels to each QWIP stack and allow simultaneous integration of the signal current in each band. We found the FPA to have high pixel operability, well balanced response, good imaging performance, high optical fill factor, and low spectral crosstalk. We present data on measurements of the noise-equivalent temperature difference of the FPA in both bands as functions of temperature and bias. The FPA data are compared to single-pixel data taken on devices from the same wafer. We also present data on the sensitivity of this FPA to polarized light. It is found that the LWIR portion of the device is very sensitive to the direction of polarization of the incident light. The MWIR part of the device is relatively insensitive to the polarization. In addition, imagery was taken with this FPA of military targets in the field. Image fusion techniques were applied to the resulting images.
A 9 micrometer cutoff 640 by 484 hand-held quantum well infrared photodetector (QWIP) camera has been demonstrated. Excellent imagery, with a noise equivalent differential temperature (NE(Delta) T) of 43 mK has been achieved. In this paper, we discuss the development of this very sensitive long wavelength infrared (LWIR) camera based on a GaAs/AlGaAs QWIP focal plane array (FPA) and its performance in quantum efficiency, NE(Delta) T, uniformity, and operability.
A 9 micrometer cutoff 256 by 256 hand-held quantum well infrared photodetector (QWIP) camera has been demonstrated. Excellent imagery, with a noise equivalent differential temperature (NE(Delta) T) of 26 mK has been achieved. In this paper, we discuss the performance of this portable long- wavelength infrared camera in quantum efficiency, NE(Delta) T, minimum resolvable temperature difference (MRTD), uniformity, etc., and its applications in science, medicine and defense.
One of the simplest device realizations of the classic particle-in-a-box problem of basic quantum mechanics is the quantum well infrared photodetector (QWIP). Optimization of the detector design and material growth and processing have culminated in the realization of a 15 micrometer cutoff 128 by 128 focal plane array camera and a camera with large (256 by 256 pixel) focal plane array of QWIPs which can see at 8.5 micrometer, holding forth great promise for a variety of applications in the 6 - 25 micrometer wavelength range. This paper discusses the physics of the QWIP and QWIP technology development at Jet Propulsion Laboratory.
In this paper, we discuss the development of very sensitive long wavelength infrared GaAs/AlxGa1-xAs quantum well infrared photodetectors (QWIPs), fabrication of random reflectors for efficient light coupling, and the demonstration of first hand-held long-wavelength 256 X 256 QWIP focal plane array camera. Excellent imagery, with a noise equivalent differential temperature of 25 mK has been achieved.
Mark Sherwin, N. Asmar, William Bewley, Keith Craig, C. Felix, B. Galdrikian, Elisabeth Gwinn, Andrea Markelz, Arthur Gossard, P. Hopkins, Mani Sundaram, Bjorn Birnir
Electrons in semiconductor nanostructures such as quantum wells can exhibit a highly nonlinear response to far-infrared radiation of sufficient intensity, such as can be supplied by the free-electron lasers (FELs) at UCSB. Several different physical mechanisms can cause nonlinear behavior in nanostructures. Experimental results at UCSB demonstrate that transport, absorption, and harmonic generation can be used as probes of nonlinear response. In the future, it may be possible to use the UCSB-FELs to observe completely new nonlinear phenomena, such as non-perturbative quantum resonances in quantum wells driven by intense far-infrared radiation.
Remotely doped parabolic quantum wells have been grown by MBE using a digital alloy approach
to vary the Al content in the AlGai.As system. The monitoring of the beam fluxes as well as
the measured subband separations confirm the precision of our growth technique. Using a front
gate electrode we can depopulate the electrical subbands. Thus we can determine experimentally
the subband separations showing close agreement with the results of our self-consistent
calculations.
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