A thirty months ESA project started in March 2008, whose purpose is to expand and assess the performance of broadband (11-15μm) quantum detectors for spectro-imaging applications: Fourier Transform Spectrometers and Dispersive Spectrometers. We present here the technical requirements, the development approach chosen as well as preliminary signal to noise ratio (SNR) calculations. Our approach is fully compatible with the final array format (1024x256, pitch 50-60μm). We expect the requested uniformity, operability and SNR levels to be achieved at the goal temperatures (60K for FTS applications and 50K for DS applications). The performance level will be demonstrated on 256x256, 50μm pitch arrays. Also, operability and uniformity issues will be addressed on large mechanical 1024x256 hybrid arrays.
Hybrid InGaAs focal plane arrays are very interesting for night vision because they can benefit from the nightglow
emission in the Short Wave Infrared band. Through a collaboration between III-V Lab and CEA-Léti, a 640x512 InGaAs
image sensor with 15μm pixel pitch has been developed.
The good crystalline quality of the InGaAs detectors opens the door to low dark current (around 20nA/cm2 at room
temperature and -0.1V bias) as required for low light level imaging. In addition, the InP substrate can be removed to
extend the detection range towards the visible spectrum.
A custom readout IC (ROIC) has been designed in a standard CMOS 0.18μm technology. The pixel circuit is based on a
capacitive transimpedance amplifier (CTIA) with two selectable charge-to-voltage conversion gains. Relying on a
thorough noise analysis, this input stage has been optimized to deliver low-noise performance in high-gain mode with a
reasonable concession on dynamic range. The exposure time can be maximized up to the frame period thanks to a rolling
shutter approach. The frame rate can be up to 120fps or 60fps if the Correlated Double Sampling (CDS) capability of the
circuit is enabled.
The first results show that the CDS is effective at removing the very low frequency noise present on the reference
voltage in our test setup. In this way, the measured total dark noise is around 90 electrons in high-gain mode for 8.3ms
exposure time. It is mainly dominated by the dark shot noise for a detector temperature settling around 30°C when not
cooled. The readout noise measured with shorter exposure time is around 30 electrons for a dynamic range of 71dB in
high-gain mode and 108 electrons for 79dB in low-gain mode.
Since 2005, Thales is successfully manufacturing QWIPs in high rate production through III-V Lab. All the early
claimed advantages of QWIPs are now demonstrated. The versatility of the band-gap engineering allows the custom
design of detectors to fulfill specific application requirements in MWIR, LWIR or VLWIR ranges. The maturity of the
III-V microelectronics based on GaAs substrates gives uniformity, stability and high production rate. In this presentation
we will discuss the specific advantages of this type of detector. An overview of the available performances and
production status will be presented including under-development products such as dual band and polarimetric sensors.
Thanks to the high transmission coefficient of short infrared wavelengths in the atmosphere and specific contrasts, SWIR
imaging is an attractive technology for space applications such as astronomical or earth observation. Detection module
must demonstrate high uniformity, sensitivity and resolution combined with compactness to meet the needs of this
application field.
Image sensors based on InGaAs photodiodes arrays present very low dark currents even at ambient temperature as high
quality materials can be grown on InP substrates. Besides, the suppression of InP substrate after hybridization is a way to
extend the detection range towards visible wavelengths. These properties result in a new generation of sensitive, compact
and multifunctional InGaAs detection modules.
In this paper, we describe the performances of an uncooled VGA InGaAs module recently developed. The 640x512 array
with a pitch of 15μm allows high resolution images. The excellent crystalline quality induces very low dark current
densities at ambient temperature. The readout circuit is based on a capacitive trans-impedance amplifier with correlated
double sampling resulting in low readout noise figure. This compact module appears as a serious alternative to the
existing technologies for low light level imaging in the [0.4μm-1.7μm] spectral range.
One of the key features of quantum well infrared photodetectors is the narrow absorption band. However, some
applications, as the infrared spectroscopy, require broadband detection. Several approaches have been used to get a
broadband response with QWIPs (superlattices, digital graded barriers, stacks, etc.). In this paper, we focus on the
interlaced configuration and on the coupled wells structure. Both designs exhibit broadband response covering the [11-15
μm] spectral range. The experimental dependencies of the spectral shape versus the temperature and bias voltage are
discussed. Based on numerical model, we propose a specific design strategy which leads to a spectral shape quasiindependent
on the operating conditions.
The Quantum Cascade Detector (QCD) is a multiple quantum well photodetector working at low bias or zero bias. It has
a zero dark current occurring at 0V, together with a high photovoltaic photoresponse, since the QCD does not need any
applied field to improve the collection of electrons. QCDs have been tested at various wavelengths, from short
wavelengths (1.5 microns) up to THz waves, through the entire infrared spectrum (middle and long wavelengths).
Theory of transport in QCD is now well established, and leads to accurate calculations of current and noise in QCDs,
with a very good agreement with experimental results. Latest results and state of the art of performances of QCDs are
presented.
Since 2002, the THALES Group has been manufacturing sensitive arrays using QWIP technology based on GaAs
and related III-V compounds, at the Alcatel-Thales-III-V Lab (formerly part of THALES Research and Technology
Laboratory).
In the past researchers claimed many advantages of QWIPs. Uniformity was one of these and has been the key
parameter for the production to start. Another widely claimed advantage for QWIPs was the so-called band-gap
engineering and versatility of the III-V processing allowing the custom design of quantum structures at various
wavelengths in MWIR, LWIR and VLWIR. An overview of the available performances of QWIPs in the whole infrared
spectrum is presented here. We also discuss about the under-development products such as dual band and
polarimetric structures.
A thirty months ESA project started in March 2008, whose overall purpose is to expand and assess the
performance of broadband (11-15 µm) quantum detectors for spectro-imaging applications: Dispersive Spectrometers
(DS) and Fourier Transform Spectrometers (FTS). We present here the technical requirements, the development
approach chosen as well as preliminary signal to noise ratio (SNR) calculations. Our approach is fully compatible with
the final array format (1024x256, pitch 50-60μm). We expect the requested uniformity, operability and SNR levels to be
achieved at the goal temperatures (60K for FTS applications and 50K for DS applications). The performance level will
be demonstrated on 256x256, 50µm pitch arrays. Also, operability and uniformity issues will be addressed on large
mechanical 1024x256 hybrid arrays.
Since 2005, the THALES Group has successfully manufactured TV/4 format QWIP sensitive arrays in high rate
production at the THALES Research and Technology Laboratory. The full-TV array manufacturing started in 2007.
Uniformity and stability were the key parameters which led to the selection of this technology for thermal cameras.
Another widely claimed advantage for QWIPs was the versatility of the band-gap engineering and of the III-V
processing allowing the custom design of quantum structures to fulfill the requirements of specific applications such as:
very long wavelength (VLWIR); multi-spectral detection; and polarimetric detection.
Serial production of CATHERINE-XP and CATHERINE-MP has now started for the various programs for which both
cameras have been selected. A review of the QWIP Production status, CATHERINE achievements and current programs
are presented. THALES has based its current strategy on very compact TI in order to address the largest range of
platforms and applications, and is working in cooperation with Sofradir and TRT / III-Vlab on the evolution of the
product to take advantage of the new capabilities offered by QWIP technology. In addition, future products based on
dual band, multi-band and polarimetric imagery are under development. An overview of these developments is presented.
Since 2002, the THALES Group has been manufacturing sensitive arrays using QWIP technology based on
GaAs and related III-V compounds, at the Alcatel-Thales-III-V Lab (formerly part of THALES Research and
Technology Laboratory).
In the past researchers claimed many advantages of QWIPs. Uniformity was one of these and has been the key
parameter for the production to start. Another widely claimed advantage for QWIPs was the so-called band-gap
engineering and versatility of the III-V processing allowing the custom design of quantum structures to fulfil the
requirements of specific applications such as very long wavelength (VLWIR) or multispectral detection. In this
presentation, we give the status of our LWIR QWIP production line, and also the current status of QWIPs for MWIR
(<5μm) and VLWIR (>15μm) arrays.
As the QWIP technology cannot cover the full electromagnetic spectrum, we develop other semiconductor
compounds for SWIR and UV applications. We present here the status of our first FPA realization in UV with GaN
alloy, and at 1.5μm with InGaAs photodiodes.
Since 2002, the THALES Group has been manufacturing sensitive arrays using QWIP technology based on GaAs and
related III-V compounds, at THALES Research and Technology Laboratory. The QWIP technology allows the
realization of large staring arrays for Thermal Imagers (TI) working in the long-wave infrared (LWIR) band (8-12
μm).
In the past researchers claimed many advantages of QWIPs. Uniformity was one of these and has been the key
parameter for the production to start. The 640x512 LWIR focal plane arrays (FPAs) with 20μm pitch was the
demonstration that state of the art performances can be achieved even with small pixels. This opened the field for the
realization of usable and affordable megapixel FPAs. Thales Research & Technology (TRT) has been developing third
generation GaAs LWIR QWIP arrays for volume manufacture of high performance low cost thermal imaging cameras.
In the past, another widely claimed advantage for QWIPs was the so-called band-gap engineering and versatility of the
III-V processing allowing the custom design of quantum structures to fulfil the requirements of specific applications
such as very long wavelength (VLWIR) or multispectral detection. In this presentation, we present the performances of
both our first 384x288, 25 μm pitch, MWIR (3-5μm) / LWIR (8-9 μm) dual-band FPAs, and the current status of
QWIPs for MWIR (< 5μm) and VLWIR (>15μm) arrays.
Since 2005, The THALES Group is successfully manufacturing TV/4 format QWIP sensitive arrays in high rate production through THALES Research and Technology.
Sofradir has entered a full production of its VEGA-LW-RM4 IDDCA using a 25μm pitch, 384x288 QWIP Array which is the core of the very compact QWIP thermal imager CATHERINE-XP.
Serial production of CATHERINE-XP has now started in THALES Optronique in order to meet the delivery schedule of the various programs for which it has been selected. A review of the QWIP Production status, CATHERINE-XP achievements and current programs are presented.
As THALES Optronique has based its today strategy on very compact TI in order to address the largest panel of platforms and applications, THALES Optronique is working in cooperation with Sofradir and TRT on the evolutions of the product to take advantage of the new capabilities offered by QWIP technology like bi-spectral or polarimetric. The achievements of these developments are also presented
We report on the first demonstration of a large format (640x512), small pitch (20&mgr;m), polarization sensitive
long-wave infrared focal plane array. The choice of quantum well infrared photodetectors allows the monolithic
integration of the polarizing element (1D gratings) into the focal plane array. The performance (response, NETD) under
natural light is identical to that of polarization insensitive focal plane arrays, with the same pitch. Polarization contrast
capabilities are investigated experimentally and are shown to be compatible with polarimetric imaging needs.
Responsivity contrasts higher than 35% are obtained, on square 18.6&mgr;m pixels. Preliminary results on extremely
compact arrays (15&mgr;m pitch) are presented.
Standard GaAs/AlGaAs Quantum Well Infrared Photodetectors (QWIP) are considered as a technological choice for
3rdgeneration thermal imagers [1], [2].
Since 2001, the THALES Group has been manufacturing sensitive arrays using AsGa based QWIP technology at
THALES Research and Technology Laboratory. This QWIP technology allows the realization of large staring arrays
for Thermal Imagers (TI) working in the Infrared region of the spectrum. The main advantage of this GaAs detector
technology is that it is also used for other commercial devices. The GaAs industry has lead to important improvements
over the last ten years and it reaches now an undeniable level of maturity. As a result the key parameters to reach high
production yield: large substrate and good uniformity characteristics, have already been achieved. Considering
defective pixels, the main usual features are a high operability (> 99.9%) and a low number of clusters having a
maximum of 4 dead pixels.
Another advantage of this III-V technology is the versatility of the design and processing phases. It allows
customizing both the quantum structure and the pixel architecture in order to fulfill the requirements of any specific
applications. The spectral response of QWIPs is intrinsically resonant but the quantum structure can be designed for a
given detection wavelength window ranging from MWIR, LWIR to VLWIR.
Standard GaAs/AlGaAs Quantum Well Infrared Photodetectors (QWIP) are now seriously considered as a technological choice for the 3rd generation of thermal imagers.
Since 2001, the THALES Group has been manufacturing sensitive arrays using QWIP technology based on AsGa techniques through THALES Research and Technology Laboratory. This QWIP technology allows the realisation of large staring arrays for Thermal Imagers (TI) working in the Infrared region of the spectrum. A review of the current QWIP products is presented (LWIR, MWIR and dual color FPAs).
The main advantage of this GaAs detector technology is that it is also used for other commercial devices. The duality of this QWIP technology has lead to important improvements over the last ten years and it reaches now an undeniable level of maturity. As a result, the processing of large substrate and a good characteristic uniformity, which are the key parameters for reaching high production yield, are already achieved. Concerning the defective pixels, the main common features are a high operability (above 99.9%) and a low number of clusters including a maximum of 5 dead pixels.
Another advantage of this III-V technology is the versatility of the design and processing phases. It allows customizing both the quantum structure and the pixel architecture in order to fulfill the requirements of any specific applications. The spectral response of QWIPs is intrinsically resonant but the quantum structure can be designed for a given detection wavelength window ranging from MWIR, LWIR to VLWIR.
THALES have developed for volume manufacture two high performance low cost thermal imaging cameras based on the THALES Research & Technology (TRT) 3rd generation gallium arsenide long wave Quantum Well Infrared Photodetector (QWIP) array. Catherine XP provides 768 x 575 CCIR video resolution and Catherine MP provides 1280 x 1024 SXGA video resolution. These compact and rugged cameras provide 24-hour passive observation, detection, recognition, and identification in the 8 to 12μm range, providing resistance to battlefield obscurants and solar dazzle, and are fully self-contained with standard power and communication interfaces. The cameras have expansion capabilities to extend functionality (for example automatic target detection) and have network battlefield capability. Both cameras benefit from the high quantum efficiency and freedom from low frequency noise of the TRT QWIP, allowing operation at 75 K, low integration times and non-interruptive non-uniformity correction. The cameras have successfully reached
technology readiness level 6/7 and have commenced environmental qualification testing in order to complete the development programmes. These latest additions to the THALES Catherine family provide high performance thermal imaging at an affordable cost.
Standard GaAs/AlGaAs Quantum Well Infrared Photodetectors (QWIP) are from now seriously considered for the 3rd generation of IR imagers for military markets. Since 2002, the THALES Group has been manufacturing sensitive arrays using QWIP technology based on AsGa
techniques through THALES Research and Technology Laboratory. This QWIP technology allows the realization of large staring arrays for Thermal Imagers (TI) working in the IR band III (8-12 μm). A review of the current QWIP products is presented. In the past researchers claimed many advantages of QWIPs. Uniformity was one of these and is the key parameter for the production start. By presenting our first results of a 640x512 LWIR FPA at a pitch of 20μm we also demonstrate that very high performances can be achieved even with small pixels which opens the field for the realization of usable and affordable
megapixel FPAs. Another advantage widely claimed in the past for QWIPs was the so-called band-gap engineering and versatility of the III-V processing allowing the custom design of quantum structure to fulfill the requirements of specific applications like very long wavelength (VLWIR) or multispectral detection. In this presentation, we present the performances of our first 256x256 MWIR / LWIR two color FPA at a pitch of 25 μm, and also the current status of QWIPs
for VLWIR arrays (>15μm).
Some parameters of integration of a Quantum Cascade Detector (QCD) in an infrared imaging system are studied. Performances of QCD are first presented : absorption and responsivity spectra, peak responsivity (around 44 mA/W), resistivity at zero bias and detectivity. Quantum efficiency and photoconduction gain are deduced from these results. Finally the consequences of an integration of such a detector in a readout circuit are studied in terms of saturation of an external capacitor.
Standard GaAs/AlGaAs Quantum Well Infrared Photodetectors (QWIPs) are from now seriously considered for the 3rd generation of IR imagers. Since 2002, the THALES Group has been manufacturing sensitive arrays using QWIP technology based on AsGa techniques through THALES Research and Technology Laboratory. This QWIP technology allows the realization of large staring arrays for Thermal Imagers (TI) working in the IR band III (8-12 μm). A review of the current QWIP products is presented. In the past researchers claimed many advantages of QWIPs. Uniformity was one of these and was the key parameter for the production start. By presenting our first results of a 640x512 LWIR FPA at a pitch of 20μm, we also demonstrate that very high performances can be achieved even with small pixels which opens the field for the realization of usable and affordable megapixel FPAs. Another advantage widely claimed in the past for QWIPs was the so-called band-gap engineering and versatility of the III-V processing. This allows the custom design of quantum structure to fulfill the requirements of specific applications like very long wavelength or multispectral detection. In this presentation, we present the performances of our first 256x256 MWIR / LWIR and LWIR/LWIR two color FPAs at a pitch of 25 μm.
Successful past experience of implementing long wave MCT 1st and 2nd Generation thermal imagers has demonstrated to THALES Optronics that MCT presents difficult challenges when correcting non-uniformity errors caused by rapidly changing detector element gain and offset drifts. These problems become even more demanding when the move is made from long linear arrays to focal plane arrays due to the significantly larger number of detector elements. Relaxation of these demands would make a significant impact on the price/performance trade which inevitably occurs in a camera development. In recognition of the need to offer UK MOD best value, THALES Optronics has initiated a programme to achieve a SXGA resolution camera and is working with UK MOD, over a two year period, to investigate whether an alternative technology can maintain the high resolution required whilst achieving a downward step change in price. The selected technology is 3rd Generation Gallium Arsenide long wave Quantum Well Infra-red Photodiode (QWIP) chosen because initial indications are that drift rates are orders of magnitude slower than MCT. The programme involves studies to determine effects of defect clusters, bimodalism, non-uniformity correction levels and higher than normal operating temperatures on achieving acceptable performance, including logistics, in user scenarios whilst maximising detector yield. Development of demonstrator IR camera hardware (technology readiness level 6/7) based on a THALES Research & Technology QWIP array is also part of the programme.
CEA/LETI has been working for several years on the development of HgCdTe-based infrared dual band detectors [3]. Since 2001 CEA/LETI is also involved in a large program for the demonstration of dual band QWIP FPAs presenting large format and small pitch. This study is carried out with the QWIP team of THALES Research and Technology (TRT) in charge of QWIP design, MBE growth and GaAs processing for the detector side. As part of this program TRT investigated different quantum structures and pixel architectures for the realization of two-band FPAs for MWIR/LWIR and LWIR/LWIR applications. At the end of this study a choice of the most appropriate architecture was done. On its side, CEA/LETI designed readout circuits optimized for the selected dual-band QWIP. TRT delivered QWIP arrays and CEA/LETI proceeded to the assembly, integration and electro-optical characterization. The aim of this paper is to describe the architecture of these dual-band demonstrators and to present the first results concerning their electro-optical performances measured at 70K and 65K.
As far as calibrated radiometric imaging is concerned, a complete prediction of oblique incidence effect on the FPA pixels’ response is required. Since a light coupling scheme needs to be used in QWIP detectors, this effect is particularly complicated to understand. This article presents two complementary test benches which allow to quantify the effect of oblique incidence on cooled infrared detectors issued from different technologies. The first test bench performs measurements over a wide angular range with low background emission levels, but gives spectrally integrated measurements. The second one delivers spectrally resolved responses for incident angles lower than 30°. In order to validate both experimental concepts, we studied QWIPs equipped with 2D periodic gratings. Relatively large pixels (100x100μm2) were chosen to ease comparison with models. Calculations based on the modal expansion method reveal that diffraction off an infinite grating does not account very well for the observed spectral responses.
Standard GaAs/AlGaAs Quantum Well Infrared Photodetectors (QWIP) are coming out from the laboratory. In this presentation we demonstrate that production and research cannot be dissociated in order to make the new generation of thermal imagers benefit as fast as possible from the building blocks developed by researchers. Since 2002, the THALES Group has been manufacturing sensitive arrays using QWIP technology based on AsGa techniques through THALES Research and Technology Laboratory. This QWIP technology, integrated in IDDCA built by Sofradir, allows the realization of large staring arrays for Thermal Imagers (TI) working in the IR band III (8-12 μm). A review of the current QWIP products, offered by Sofradir, is presented. In the past researchers claimed many advantages of QWIPs. Uniformity was one of these and was the key parameter for the production start. Another advantage widely claimed also for QWIPs was the so-called band-gap engineering, allowing the custom design of quantum structure to fulfill the requirements of specific applications like very long wavelength or multispectral detection. In this presentation, we present the performances for Middle Wavelength InfraRed (MWIR) detection and demonstrate the ability of QWIP to cover the two spectral ranges (3-5 μm and 8-20 μm). At last but not least, the versatility of the GaAs processing appeared for QWIPs as an important gift. This assumption was well founded. We give here some results achieved on building blocks for two color QWIP pixels. We also report the expected performances of focal plane arrays we are currently developing with the CEA-LETI-SLIR.
This presentation deals with the following aspects: The THALES Group has successfully manufactured sensitive arrays using QWIP technology based on AsGa techniques through THALES Research and Technology Laboratory. This QWIP technology allows the manufacturing of staring arrays for Thermal Imagers (TI) working in LWIR band (8 - 12 μm). A review of this QWIP technology is presented. The THALES Group is offering a complete range of TI for several applications, from Hand Held version to integrated versions in sight, surveillance system and gimbal. The basic choice for TI used in land applications on the battlefield remains the LWIR band. THALES Optronique has based its today strategy on very compact TI in order to allow the largest panel of applications for hand held and vehicle applications. An overview of the achieved performances and applications is presented. The current developments allowing to take the best part of the QWIP technology are also presented.
Standard GaAs/AlGaAs QWIPs are now well established for LWIR detection. The main advantage of this technology is the duality with the technology of commercial GaAs devices. The realization of large FPAs (up to 640 X 480) drawing on the standard III-V technological process has already been demonstrated. The second advantage widely claimed for QWIPs is the so-called band-gap engineering, allowing the custom design of the quantum structure to fulfill the requirements of specific applications such as multispectral detection. QWIP technology has been growing up over the last ten years and now reaches an undeniable level of maturity. As with all quantum detectors, the operating temperature of QWIPs is limited by the thermal current, particularly in the LWIR range. It is very crucial to achieve an operating temperature as high as possible and at least above 77 K in order to reduce volume and power consumption and to improve the reliability of the detection module. This thermal current offset has three detrimental effects: noise increase, storage capacitor saturation and high sensitivity of FPAs to fluctuations in operating temperature. For LWIR FPAs, large cryocoolers are required, which means volume and power consumption unsuitable for handheld systems. The understanding of detection mechanisms has led us to design and realize high performance 'standard' QWIPS working near 77 K. Furthermore, a new in situ skimmed architecture accommodating this offset has already been demonstrated. In this paper we summarize the contribution of THALES Research & Technology to this progress. We present the current status of QWIPs in France, including the latest performances achieved with both standard and skimmed architectures. We illustrate the development of our QWIPs by results on FPAs.
Standard GaAs/AlGaAs QWIPs are now well established for LWIR detection. The main advantage of this technology is the duality with the technology of commercial GaAs devices. The second advantage widely claimed for QWIPs is the so-called band-gap engineering, allowing the custom design of the quantum structure to fulfill the requirements of specific applications such as multispectral detection. QWIPS are close to being optimized. The understanding of detection mechanisms has led to high performance QWIPs working at high temperature (above 77 K). However, as with all quantum detectors, the operating temperature of QWIPs is limited by the thermal current. A new skimmed architecture accommodating this offset has already been demonstrated. The optimization of a skimmed structure requires the modeling procedures and the process, to be adapted. We present the current status of QWIPs in France, including the latest performances achieved with both standard and skimmed architectures. We illustrate the development of our QWIPs by recent results on FPAs.
Standard GaAs/AlGaAs Quantum Well IR Photodetectors (QWIP) are now well established for long wavelength IR (LWIR) detection. The first advantage of this technology is the duality with the technology of commercia GaAs devices. The realization of large focal plane arrays employing the standard III-V technological processes is already demonstrated. The second advantage widely claimed for QWIPs is the so-called band-gap engineering, allowing the custom design of the quantum structure to fulfill the requirements of specific applications like multispectral detection. In this paper, we present electro-optical results on Middle Wavelength IR (MWIR) detectors. We demonstrate the ability of QWIPs to cover the two spectral ranges. As the operating temperature is crucial for commercial thermal images, we report the temperature dependence of the performances of our MWIR QWIP detector up to 150 K. Performances of QWIPs in the MWIR with the implementation of the new skimming architecture are discussed.
The Laboratoire Central de Recherches (LCR) of Thomson Csf and the Societe Francaise de Detecteurs Infrarouge (Sofradir) combined their complementary skills to realize a MultiQuantum Well Infrared Photodetector (QWIP) Focal Plane Array (FPA) sensitive in the long wavelength range of the spectrum (LWIR). Sofradir has industrialized a versatile indium bump hybridization technics qualified for operations as low as 50 K and mostly dedicated to connection of Cadmium Mercury Telluride (CMT) PhotoVoltaic (PV) detectors to silicon Read- Out Integrated Circuits (ROIC). On the other hand, the Thomson Csf/Lcr's QWIP technology based on GaAs/AlGaAs heterostructures is now suitable for industrial development. The device described in this paper is a first generation 144 X 192 MQW staring arrays with a 50 microns pitch; it is operated at temperature as high as 80 K. Such a high operating temperature can be achieved thanks to the optimized design of the QWIP active layer and to the use of a multi purpose experimental CMOS ROIC integrating a current skimming function; this structure developed for high temperature operation of CMT detectors allows for in pixel calibration and derivation of photosite current containing no scene information (e.g. dark and background current) and thus offers enhanced effective storage capacity. In this paper, the main features of the hybrid are given showing the adequacy of this hybridization technics to connecting the QWIP structures. A functional description of the ROIC is presented together with its advantages and limitations in terms of conditions at operating temperature of 70 K and 80 K are thoroughly presented and discussed, in particular in reference with the equivalent CMT performances.
A novel architecture for both QWIP heterostructure and pixel design is described. This new approach completely eliminates the dark current of a conventional GaAs/GaAlAs multiple quantum well LWIR detector. The concept is first described, then the industrial feasibility is demonstrated on a 4 X 2 array with 50 micrometer pixel pitch. The performance modeling of FPA based on this new design shows that NETD as low as 15 mK is achievable at an operating temperature of 90 K and for arrays with 30 micrometer pitch.
During the last decade, the QWIPs technology has improved from start to an undeniable maturity level. High performance focal plane arrays have already been realized (ATT, Lockheed-Martin, JPL, . . .) with a spectacular format increase ranging from 128 by 128 up to 640 by 480, and images from bicolor 256 by 256 arrays have been shown last year. All these devices illustrate the high potential of the QWIP technology. In the same time, the modeling of detection mechanism has advanced to permit the present design of specific detectors and their optimization in given operating environments (near 77 K detector temperature for instance). In this communication, we summarize our recent technological studies leading to the next generation of very large infrared detector arrays. We present the QWIP ultimate performances allowed by the standard dual III - V technological processes developed at THOMSON CSF, in terms of pixel size, array filling factor or connectics. The influence of the pixel size for the grating optical coupling is analyzed. We finally include in this analysis our results for more complex devices like multispectral infrared detectors.
Quantum well infrared photodetectors (QWIPs) form a new generation of infrared detectors based on carrier confinement in ultrathin semiconductor heterostructures. The artificial energy levels in these wells can be tailored to match any optical transition in the 3 - 20 micrometer photon wavelength range by adjusting the quantum well width and the barrier composition. In this communication, we summarize our present understanding of the physics of QWIP detection: photoexcited carrier emission and capture probability, contact injection, and noise mechanisms. We also present the performances of optimized devices for the infrared Detection in the 3 - 5 micrometer and 8 - 12 micrometer wavelength ranges. We also illustrate the major advantages of this new technology for infrared staring arrays: (1) standard III-V substrates and technology, thermal stability, uniformity, large areas, low development costs, radiation hardness, (2) adjustability from 3 to 20 micrometer, (3) new functions: multispectrality, spectrophotometry, band switching, optical reading.
Transitions between the subbands of quantum wells have extremely large oscillator strengths. Since
second-order nonlinear optical coefficients are proportional to the square of oscillator strength, strong
nonlinear effects are expected in such systems, provided inversion symmetry is broken. This paper reviews
the main results (optical rectification, second harmonic generation) obtained in structures in which the
symmetry breaking has been realized by growing AlGaAs multiquantum wells with asymmetrical Al
gradients. We show that, in these structures, the dipole matrix elements have magnitudes comparable to the
well thicknesses, i.e. in the few nanometers range instead of the few picometers usually found in
molecules. These Compositionally Asymmetrical multiquantum wells may thus be viewed as giant
"quasi-molecules" optimized for optical nonlinearities in the mid infared.
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