Quantum Well Infrared Photodetector Focal Plane Array Research Articles

High-Discrimination Circular Polarization Detection Based on Dielectric-Metal-Hybrid Chiral Metamirror Integrated Quantum Well Infrared Photodetectors.

Circular polarization detection enables a wide range of applications. With the miniaturization of optoelectronic systems, integrated circular polarization detectors with native sensitivity to the spin state of light have become highly sought after. The key issues with this type of device are its low circular polarization extinction ratios (CPERs) and reduced responsivities. Metallic two-dimensional chiral metamaterials have been integrated with detection materials for filterless circular polarization detection. However, the CPERs of such devices are typically below five, and the light absorption in the detection materials is hardly enhanced and is even sometimes reduced. Here, we propose to sandwich multiple quantum wells between a dielectric two-dimensional chiral metamaterial and a metal grating to obtain both a high CPER and a photoresponse enhancement. The dielectric-metal-hybrid chiral metamirror integrated quantum well infrared photodetector (QWIP) exhibits a CPER as high as 100 in the long wave infrared range, exceeding all reported CPERs for integrated circular polarization detectors. The absorption efficiency of this device reaches 54%, which is 17 times higher than that of a standard 45° edge facet coupled device. The circular polarization discrimination is attributed to the interference between the principle-polarization radiation and the cross-polarization radiation of the chiral structure during multiple reflections and the structure-material double polarization selection. The enhanced absorption efficiency is due to the excitation of a surface plasmon polariton wave. The dielectric-metal-hybrid chiral mirror structure is compatible with QWIP focal plane arrays.

Nature Allows High Sensitivity Thermal Imaging With Type-I Quantum Wells Without Optical Couplers: A Grating-Free Quantum Well Infrared Photodetector With High Conversion Efficiency

Quantum well infrared photodetectors (QWIPs) have facilitated thermal imagers with excellent pixel operability, uniformity and stability. The main disadvantage of the standard QWIP technology is the low conversion efficiency (CE) as a result of weak quantum efficiency (QE) and photoconductive gain inhibiting the utilization of the sensor for low background and/or high frame rate applications. The other problem is the requirement of an optical grating which loses its efficiency with decreasing pixel pitch, as well as limiting the performance of dual-band focal plane array (FPA) due to the wavelength dependence of the diffraction-grating coupling efficiency. The author reports a grating-free 15 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> pixel pitch <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$640\times 512$ </tex-math></inline-formula> mid-wavelength infrared (MWIR) QWIP FPA constructed with the InP/GaInP/In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.83</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.17</sub> As material system with normal incident radiation absorption ability. The pixels yielded peak QE, CE and specific detectivity of 23%, ~40% and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times 10 ^{11}$ </tex-math></inline-formula> cmHz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> /W (at ~80 K with f/2 optics) in spite of the absence of diffraction grating, substantially high cut-off wavelength (5.8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> ) and broad spectral response ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \lambda /\lambda _{\mathbf {p}}=31$ </tex-math></inline-formula> %). Together with excellent (uncorrected) responsivity and noise equivalent temperature difference nonuniformities of 5.9% and 17%, the results illustrate tremendous improvement over the performance of the conventional MWIR QWIP FPA exhibiting great potential to revive the QWIP technology especially in dual-band imaging.

QWIP focal plane array theoretical model of 3-D imaging LADAR system

The aim of this research is to develop a model for the direct detection three-dimensional (3-D) imaging LADAR system using Quantum Well Infrared Photodetector (QWIP) Focal Plane Array (FPA). This model is employed to study how to add 3-D imaging capability to the existing conventional thermal imaging systems of the same basic form which is sensitive to 3–5 µm(mid-wavelength infrared, MWIR) or 8–12 µm (long-wavelength infrared, LWIR) spectral bands. The integrated signal photoelectrons in case of short integration time is required to transmit laser pulses with higher energy in order to obtain photoelectrons nearest those values obtained from the background photoelectrons in thermal imaging system with the longer interval of time. Since the operating conditions of the proposed system are of low levels for speckle diversity and high levels of signal photoelectrons, it was shown that the signal obeys the Gaussian probability density function. The evaluation of system performance of the proposed model shows that it needs a detector with low dark current and high transmitted energy to obtain satisfactory parameter values.

1/f Noise QWIPs and nBn detectors

The low-frequency noise is a ubiquitous phenomenon and the spectral power density of this fluctuation process is inversely proportional to the frequency of the signal. We have measured the 1/f noise of a 640×512 pixel quantum well infrared photodetector (QWIP) focal plane array (FPA) with 6.2μm peak wavelength. Our experimental observations show that this QWIP FPA’s 1/f noise corner frequency is about 0.1mHz. With this kind of low frequency stability, QWIPs could unveil a new class of infrared applications that have never been imagined before. Furthermore, we present the results from a similar 1/f noise measurement of bulk InAsSb absorber (lattice matched to GaSb substrate) nBn detector array with 4.0μm cutoff wavelength.

Diffraction-Grating-Coupled High Quantum Efficiency InP/InGaAs Quantum Well Infrared Photodetector Focal Plane Array

Quantum well infrared photodetector (QWIP) is still the sole field proven low-cost long-wavelength infrared photon sensor. We report an impressively high quantum efficiency of 31% in the pixels of a large format (640 × 512) grating-coupled InP/In0.48Ga0.52As QWIP focal plane array (FPA). The InP/InGaAs QWIP FPA with a cut-off wavelength of ~ 9 μm provided desirable characteristics at a temperature as high as 78 K. The noise-equivalent temperature difference of the FPA with f/2 optics is ~ 30 mK with an integration time as low as 1 ms at 67 K. We also present a thorough comparison of InP and GaAs-based QWIPs for long-wavelength infrared thermal imaging and shed light on the characteristic differences between these devices to be used as a guide for improving the performance of this important sensor technology. The results clearly indicate that the main limitations of the standard QWIP technology can be overcome through the utilization of alternative material systems and proper FPA processing techniques.

Broadband QWIP FPAs for hyperspectral applications

Is a quantum well infrared photodetector (QWIP) suitable for hyperspectral applications? Yes, provided its spectral response is broad enough, the signal-to-noise ratio in narrow spectral slices across the entire response band is high enough, and the operating temperature is reasonable. We present the performance of a 640×512 QWIP focal plane array (FPA) with nearly uniform spectral response from 8 to 12μm that achieves temporal noise equivalent temperature difference (NETD) lower than 200mK in 20nm wide spectral slices across the entire 8–12μm band with the FPA operating at a temperature of 50K or colder. A hyperspectral camera would feature a grating or prism to disperse 8–12μm light across such a FPA or a hyperspectral filter on top of the FPA. Operating in pushbroom mode on an earth-observing satellite, the camera can be used for spectral mapping of vegetation, crops and forests, for pollution monitoring, and for studies in atmospheric chemistry.

Design and characterization of a CMOS preamplifier for quantum well infrared photodetectors

A preamplifier based on the source-follower direct injection (SFDI) topology for use in read-out integrated circuits (ROIC) of quantum-well infrared photodetectors focal plane arrays (QWIP-FPA) is demonstrated. The fabricated circuit shows high linearity, high integration time (from hundreds of μs to few ms) and low current detection capabilities for a wide range of input current (order of few pA). This performance was achieved through the use of a Poly1-Poly2 capacitor that, although presenting some penalties in area consumption, provides a higher linearity, lower leakage current and higher temperature stability than all others capacitors found in literature. Secondary effects such as charge injection and clock feed-through are observed in the experimental results and classical techniques, like the use of DUMMY transistor, are shown to be effective in minimizing these effects and maximizing the linearity of the response. The overall results indicate that this circuit architecture has a great potential to be practically integrated in larger QWIP-FPA ROICs, showing an improved performance relating to previous works in literature.

High speed QWIP FPAs on InP substrates

Quantum well infrared photodetector (QWIP) technology has allowed the realization of low cost staring focal plane arrays (FPAs). However, AlGaAs/(In)GaAs QWIP FPAs suffer from low quantum and conversion efficiencies under high frame rate and/or low background conditions. We extensively discuss the effect of sensor gain on the FPA performance under various operating conditions, and highlight the superiority of the InP/InGaAs material system with respect to AlGaAs/GaAs for high speed/low background thermal imaging applications. InP/InGaAs QWIPs, providing a bias adjustable gain in a wide range, offer the flexibility of adapting the FPA to strict operating conditions. We also present an experimental comparison of large format AlGaAs/GaAs and (strained) InP/InGaAs QWIP FPAs under different operating conditions. A 640 × 512 QWIP FPA constructed with the 40-well strained InP/In 0.48Ga 0.52As material system displays a cut-off wavelength of 9.7 μm ( λ p = 8.9 μm) with a BLIP temperature higher than 65 K ( f/2), and a peak quantum efficiency as high as 12% with a broad spectral response (Δ λ/ λ p = 17%). The conversion efficiency of the FPA pixels is as high as 20% under large bias (4 V) where the detectivity is reasonably high (∼3 × 10 10 cm Hz 1/2/W, f/2, 65 K). While providing a considerably higher quantum efficiency than the pixels of a similar AlGaAs/GaAs FPA, the InP/InGaAs QWIP provides similar NETD values with much shorter integration times and, being less sensitive to the read noise, successfully operates with sub-millisecond integration times. The results clearly demonstrate that InP based material systems display high potential for single- and dual-band QWIP FPAs by overcoming the limitations of the standard GaAs based QWIPs under high frame rate and/or low background conditions.

Large area III–V infrared focal planes

Jet Propulsion Laboratory is actively developing the III–V based infrared detector and focal plane arrays (FPAs) for remote sensing and imaging applications. Currently, we are working on Superlattice detectors, multi-band quantum well infrared photodetectors (QWIPs), and quantum dot infrared photodetector (QDIPs) technologies suitable for high pixel-pixel uniformity and high pixel operability large area imaging arrays. In this paper, we will discuss the demonstration of long-wavelength 1 K × 1 K QDIP FPA, 1 K × 1K QWIP FPA, the first demonstration of the megapixel-simultaneously-readable and pixel-co-registered dual-band QWIP FPA, and demonstration of the first mid-wave and long-wave 1K × 1K superlattice FPA. In addition, we will discuss the advantages of III–V material system in the context of large format infrared FPAs.

Optimization of broadband (11–15 μm) optical coupling in Quantum Well Infrared Photodetectors for space applications

Large format detectors in the long wavelength region of the thermal infrared (TIR) spectrum ( λ ∼ 11–15 μm) with very high radiometric and imaging performances are of increasing scientific and operational interest for, e.g. meteorology and atmospheric chemistry in missions such as Meteosat Third Generation (MTG) or Planetary Science missions. A 30 months ESA project started in 2008, whose overall purpose is to expand and assess the performance of broadband 11–15 μm Quantum Well Infrared Photodetectors (QWIP) for spectro-imaging applications: Dispersive Spectrometers (DS) and Fourier Transform Spectrometers (FTS). The primary objective is the development of an optimized detection layer focusing on its technology and the necessary performance levels. In this paper, we present a theoretical and experimental study of the optical coupling inside the pixels of a QWIP focal plane array. The broadband 11–15 μm absorption spectrum is achieved by the use of a quantum well stack containing several kinds of quantum wells. The natural narrowband optical coupling of classical diffraction gratings doesn’t allow an efficient and uniform broadband optical coupling of the IR incident light over the whole 11–15 μm spectral band. Specific aperiodic or quasiperiodic optical coupling schemes have to be used. In this work we demonstrate the ability of obtaining a good spectral matching with various original broadband diffractive structures. An extensive experimental study is presented. Comparison with simulated spectra is performed.

Quantum well infrared photodetector simultaneously working in two atmospheric windows

We have demonstrated a two-contact quantum well infrared photodetector (QWIP) exhibiting simultaneous photoresponse in both the mid- and the long-wavelength atmospheric windows of 3-5 mu m and of 8-12 mu m. The structure of the device was achieved by sequentially growing a mid-wavelength QWIP part followed by a long-wavelength QWIP part separated by an n-doped layer. Compared with the conventional dual-band QWIP device utilizing three ohmic contacts, our QWIP is promising to greatly facilitate two-color focal plane array (FPA) fabrication by reducing the number of the indium bumps per pixel from three to one just like a monochromatic FPA fabrication and to increase the FPA fill factor by reducing one contact per pixel; another advantage may be that this QWIP FPA boasts broadband detection capability in the two atmospheric windows while using only a monochromatic readout integrated circuit. We attributed this simultaneous broadband detection to the different distributions of the total bias voltage between the mid- and long-wavelength QWIP parts.

High Conversion Efficiency InP/InGaAs Strained Quantum Well Infrared Photodetector Focal Plane Array With 9.7 $\mu$m Cut-Off for High-Speed Thermal Imaging

InP/InGaAs material system is an alternative to AlGaAs/GaAs for long wavelength quantum well infrared photodetectors (QWIPs). We demonstrate a large format (640 × 512) QWIP focal plane array (FPA) constructed with the strained InP/InGaAs material system. The strain introduced to the structure through utilization of In0.48Ga0.52As (instead of In0.53Ga0.47As ) as the quantum well material shifts the cut-off wavelength from ˜8.5 to 9.7 μm. The FPA fabricated with the 40-well epilayer structure yields a peak quantum efficiency as high as 12% with a broad spectral response (Δλ/p=17%). The peak responsivity of the FPA pixels is 1.4 A/W corresponding to 20% conversion efficiency in the bias region where the detectivity is reasonably high (2.6 × 1010 cm Hz1/2/W, f/1.5, 65 K). The FPA providing a background limited performance temperature higher than 65 K (f/1.5) satisfies the requirements of most low integration time/low background applications where AlGaAs/GaAs QWIPs suffer from read-out circuit noise limited sensitivity due to lower conversion efficiencies. Noise equivalent temperature differences of the FPA are as low as 19 and 40 mK with integration times as short as 1.8 ms and 430 μs (f/1.5, 65 K).

Demonstration of Megapixel Dual-Band QWIP Focal Plane Array

Quantum well infrared photodetectors (QWIPs) are well known for their stability, high pixel-pixel uniformity and high pixel operability which are quintessential parameters for large area imaging arrays. In this paper we report the first demonstration of the megapixel-simultaneously-readable and pixel-co-registered dual-band QWIP focal plane array (FPA). The dual-band QWIP device was developed by stacking two multi-quantum-well stacks tuned to absorb two different infrared wavelengths. The full width at half maximum (FWHM) of the midwave infrared (MWIR) band extends from 4.4-5.1 ?m and FWHM of the long-wave infrared (LWIR) band extends from 7.8-8.8 ?m. Dual-band QWIP detector arrays were hybridized with direct injection 30 ?m pixel pitch megapixel dual-band simultaneously readable CMOS read out integrated circuits using the indium bump hybridization technique. The initial dual-band megapixel QWIP FPAs were cooled to 68 K operating temperature. The preliminary data taken from the first megapixel QWIP FPA has shown system NE?T of 27 and 40 mK for MWIR and LWIR bands, respectively.

Large format voltage tunable dual-band QWIP FPAs

Third generation thermal imagers with dual/multi-band operation capability are the prominent focus of the current research in the field of infrared detection. Dual band quantum-well infrared photodetector (QWIP) focal plane arrays (FPAs) based on various detection and fabrication approaches have been reported. One of these approaches is the three-contact design allowing simultaneous integration of the signals in both bands. However, this approach requires three In bumps on each pixel leading to a complicated fabrication process and lower fill factor. If the spectral response of a two-stack QWIP structure can effectively be shifted between two spectral bands with the applied bias, dual band sensors can be implemented with the conventional FPA fabrication process requiring only one In bump on each pixel making it possible to fabricate large format dual band FPAs at the cost and yield of single band detectors. While some disadvantages of this technique have been discussed in the literature, the detailed assessment of this approach has not been performed at the FPA level yet. We report the characteristics of a large format (640 × 512) voltage tunable dual-band QWIP FPA constructed through series connection of MWIR AlGaAs–InGaAs and LWIR AlGaAs–GaAs multi-quantum well stacks, and provide a detailed assessment of the potential of this approach at both pixel and FPA levels. The dual band FPA having MWIR and LWIR cut-off wavelengths of 5.1 and 8.9 μm provided noise equivalent temperature differences as low as 14 and 31 mK ( f/1.5) with switching voltages within the limits applicable by commercial read-out integrated circuits. The results demonstrate the promise of the approach for achieving large format low cost dual band FPAs.

QWIP focal plane arrays on InP substrates for single and dual band thermal imagers

Alternative material systems on InP substrate provide certain advantages for mid-wavelength infrared (MWIR), long-wavelength infrared (LWIR) and dual band MWIR/LWIR quantum well infrared photodetector (QWIP) focal plane arrays (FPAs). While InP/InGaAs and InP/InGaAsP LWIR QWIPs provide much higher responsivity when compared to the AlGaAs/GaAs QWIPs, AlInAs/InGaAs system facilitates completely lattice matched single band MWIR and dual band MWIR/LWIR FPAs. We present an extensive review of the studies on InP based single and dual band QWIPs. While reviewing the characteristics of InP/InGaAs and InP/InGaAsP LWIR QWIPs at large format FPA level, we experimentally demonstrate that the cut-off wavelength of AlInAs/InGaAs QWIPs can be tuned in a sufficiently large range in the MWIR atmospheric window by only changing the quantum well (QW) width at the lattice matched composition. The cut-off wavelength can be shifted up to ∼5.0 μm with a QW width of 22 Å in which case very broad spectral response (Δ λ/ λ p = ∼30%) and a reasonably high peak detectivity are achievable leading to a noise equivalent temperature difference as low as 14 mK ( f/2) with 25 μm pitch in a 640 × 512 FPA. We also present the characteristics of InP based two-stack QWIPs with wavelengths properly tuned in the MWIR and LWIR bands for dual color detection. The results clearly demonstrate that InP based material systems display high potential for dual band MWIR/LWIR QWIP FPAs needed by third generation thermal imagers.

1024 × 1024 Format pixel co-located simultaneously readable dual-band QWIP focal plane

This paper reports the first demonstration of the megapixel-simultaneously-readable and pixel-co-registered dual-band quantum well infrared photodetector (QWIP) focal plane array (FPA). The dual-band QWIP device was developed by stacking two multi-quantum-well stacks tuned to absorb two different infrared wavelengths. The full width at half maximum (FWHM) of the mid-wave infrared (MWIR) band extends from 4.4 to 5.1 μm and the FWHM of a long-wave infrared (LWIR) band extends from 7.8 to 8.8 μm. Dual-band QWIP detector arrays were hybridized with custom fabricated direct injection read out integrated circuits (ROICs) using the indium bump hybridization technique. The initial dual-band megapixel QWIP FPAs were cooled to 70 K operating temperature. The preliminary data taken from the first megapixel QWIP FPA has shown system NEΔT of 27 and 40 mK for MWIR and LWIR bands, respectively.

Voltage-Tunable Two-Color Corrugated-QWIP Focal Plane Arrays

We demonstrated a 256 times 256 voltage-tunable two- color corrugated quantum-well infrared-photodetector focal plane array. The detector operation is based on photocurrent asymmetry in a double-superlattice quantum well structure. By using a broadband corrugated light coupling scheme, we obtained a quantum efficiency of 24% in the mid-wave (MW) band and 26% in the long-wave (LW) band without AR coating. Operating at 50 K, the measured noise equivalent temperature difference is 27 mK at 33-ms integration time for the MW and 90 mK at 2 ms for the LW with f/2.44 optics. The NETD operability values are 98.4% and 95.9%, respectively.

Lattice-matched AlInAs–InGaAs mid-wavelength infrared QWIPs: characteristics and focal plane array performance

The AlInAs/InGaAs material system is promising for mid-wavelength infrared (MWIR) and multi-band quantum well infrared photodetectors (QWIPs) as a lattice-matched alternative to the strained AlGaAs/InGaAs system. In this paper, we report a large format (640 × 512) AlInAs/InGaAs QWIP focal plane array (FPA) with 4.9 µm cut-off wavelength and assess the performance of this material system for MWIR QWIP applications at both pixel and large format FPA level. We also experimentally demonstrate that the cut-off wavelength of AlInAs/InGaAs QWIPs can be tuned in a sufficiently large range in the MWIR atmospheric window by changing only the quantum well (QW) width at the lattice-matched composition. The cut-off wavelength is shifted from 4.15 to 4.9 µm when the QW width is decreased from 30 to 23 Å, in which case a very broad spectral response (Δλ/λp = 32%) with a reasonably high peak detectivity (5.5 × 1010 cm Hz1/2 W−1, f/1.5) is achievable. The AlInAs/InGaAs QWIP FPA yielded excellent sensitivity with a noise equivalent temperature difference as low as 22 mK and a background limited performance (BLIP) temperature as high as 115 K with f/1.5 aperture and 300 K background. The results clearly demonstrate the potential of this material system for completely lattice-matched dual- or multi-band QWIP FPAs for third-generation thermal imagers.

Large-Format Voltage-Tunable Dual-Color Midwavelength Infrared Quantum-Well Infrared Photodetector Focal Plane Array

We report a large-format (640 times 512) voltage-tunable quantum-well infrared photodetector (QWIP) focal plane array (FPA) for dual-color imaging in the midwavelength infrared (3-5 mum) band. Voltage-tunable spectral response has been achieved through series connection of two eight-well stacks of AlGaAs-InGaAs epilayers grown by molecular beam epitaxy on GaAs substrate. The peak responsivity wavelength of the detectors is shifted from 4.1 mum (color 1) to 4.7 mum (color 2) as the bias is increased within the limit applicable by commercial read-out integrated circuits. The operability of the FPA is ~99.5% with noise equivalent temperature differences of ~60 and 30 mK (f/1.5) in color modes 1 and 2, respectively. To our knowledge, this is the first large-format voltage-tunable dual-color QWIP FPA reported for midwavelength thermal imaging.

Quantum Well and Quantum Dot Based Detector Arrays for Infrared Imaging

ABSTRACTA mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) 320x256 pixel quantum well infrared photodetector (QWIP) dualband focal plane arrays (FPAs) have been demonstrated with excellent imagery. Currently, we are developing a 1024x1024 pixel simultaneous pixel co-registered dualband QWIP FPA. In addition, epitaxially grown self-assembled InAs/InGaAs/GaAs quantum dots (QDs) are exploited for the development of large-format FPAs. The Dot-in-a-Well (DWELL) structures were experimentally shown to absorb both 45° and normal incident light, therefore a reflection grating structure was used to enhance the quantum efficiency. The devices exhibit peak responsivity out to 8.1 microns, with peak detectivity reaching ∼ 1 × 1010 Jones at 77 K. The devices were fabricated into the first LWIR 640x512 pixel QDIP FPA, which has produced excellent infrared imagery with NETD of 40 mK at 60K operating temperature.