Quantum Well Infrared Photodetectors Technology Research Articles

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.

High-x InP/InxGa1−xAs quantum well infrared photodetector

Quantum well infrared photodetector (QWIP) technology is still the only thermal imaging sensor technology providing excellent pixel operability, uniformity and stability together with low production cost and insignificant 1/f noise. The main bottleneck of the standard QWIP technology is the low quantum efficiency and device gain inhibiting the utilization of the sensor for low background and/or high frame rate applications. This manuscript reports unusually high quantum efficiency observed in mid-wavelength infrared (MWIR) QWIPs constructed with solid-source molecular beam epitaxy grown thirty In0.83Ga0.17As quantum wells sandwiched between InP and GaInP barriers. Large area (300 × 300 μm2) bound-to-continuum detectors with ∼5.7 μm cut-off wavelength exhibited very broad (Δλ/λp = ∼40%) responsivity spectrum together with impressively high peak absorption quantum efficiency of ∼20% and a 78 K peak specific detectivity above 1 × 1011 cmHz 1/2/W with f/2 optics in the absence of diffraction grating. Even higher signal-to-noise ratio was observed in grating-free small area (∼20 × 20 µm2) detectors hybridized to a fan-out substrate. Considering the expected improvements in the quantum efficiency by confining the responsivity spectrum to the narrower (and useful) wavelength region in the MWIR band and utilization of diffraction grating, the results presented in this manuscript have considerable potential to open the door to reshape the QWIP technology.

Advantages of QWIP technology in infrared thermal cameras

Standard GaAs/AlGaAs quantum well infrared photodetectors (QWIP) have been seriously considered as atechnological choice for the 3rd generation of thermal imagers in the long wave infrared band (LWIR) for some time. Alternative technology like MCT (HgCdTe) was the technology choice of the 2nd generation because of its high quantum efficiency. In the paper, measurements on the QWIP technology will be presented and a comparison with alternative technology will be done.

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.

Quantum well infrared photodetectors: present and future

A review of the III-V Lab activities in the field of quantum well infrared photodetectors (QWIPs) is presented. We discuss the specific advantages of this type of detector and present the production facilities and status. A large section is dedicated to broadband QWIPs for space applications and to QWIPs on InP for mid-wavelength infrared detection. We review the progress of QWIP technology for the next generation (dual band, polarimetric, and multispectral) of thermal imagers. Finally, the state-of-the-art of very long wavelength QWIPs is discussed.

Status of quantum well infrared photodetector technology at QmagiQ today

The current state of focal plane arrays (FPAs) made from quantum well infrared photodetectors (QWIPs) is presented. In the last decade, QWIP technology has successfully transitioned at several companies from research and development to manufacturing and, today, represents a commercial success in cooled high-performance longwave infrared imaging. Technical performance metrics such as quantum efficiency, temporal and spatial noise, maximum frame rate and operating temperature, array uniformity and pixel operability, and manufacturing reproducibility are presented.

Development of a 1K × 1K, 8–12 μm QWIP array

In the on-going evolution of GaAs quantum well infrared photodetectors (QWIPs) we have developed a 1,024×1,024 (1K×1K), 8–12 μm infrared focal plane array (FPA). This 1 megapixel detector array is a hybrid using an L3/Cincinnati Electronics silicon readout integrated circuit (ROIC) bump bonded to a GaAs QWIP array fabricated jointly by engineers at the Goddard Space Flight Center (GSFC) and the Army Research Laboratory (ARL). We have integrated the 1K×1K array into an SE-IR based imaging camera system and performed tests over the 50–80K temperature range achieving BLIP performance at an operating temperature of 57K. The GaAs array is relatively easy to fabricate once the superlattice structure of the quantum wells has been defined and grown. The overall arrays costs are currently dominated by the costs associated with the silicon readout since the GaAs array fabrication is based on high yield, well-established GaAs processing capabilities. One of the advantages of GaAs QWIP technology is the ability to fabricate arrays in a fashion similar to and compatible with silicon IC technology. The designer’s ability to easily select the spectral response of the material from 3μm to beyond 15μm is the result of the success of band-gap engineering and the Army Research Lab is a leader in this area. In this paper we will present the first results of our 1K×1K QWIP array development including fabrication methodology, test data and imaging capabilities.

QWIP products and building blocks for high performance systems

Standard GaAs/AlGaAs quantum well infrared photodetectors (QWIP) are coming out from the laboratory. In this paper 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 GaAs 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 initiation. 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 paper, we present the performances for Middle Wavelength InfraRed (MWIR) detections and demonstrate the ability of QWIP’s to cover the two spectral ranges (3–5 μm and 8–20 μm). 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 that we are currently developing with the CEA-LETI-SLIR.

QWIP detectors and thermal imagers

Standard GaAs/AlGaAs QWIPs (Quantum Well Infrared Photodetector) are now well established for long wave infrared (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 640×480) 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 thermal current, particularly in the LWIR range, limits the operating temperature of QWIPs. 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 potential of our QWIPs through features of Thales Optronique's products for third thermal imager generation. To cite this article: E. Costard et al., C. R. Physique 4 (2003).

QWIP or other alternative for third generation infrared systems

Choosing the right detector technology for third generation thermal imaging systems is directly derived from the requirements of these new generation infrared imaging systems. It is now evident that third generation thermal imager will still need the higher resolution capabilities as well as capabilities in multispectral detection and polarization sensitivity. Four technologies candidates are analyzed; the field-proved HgCdTe (MCT), uncooled microbolometer technology, antimonide based materials and quantum well infrared photodetectors (QWIP). Taking into account the risks, maturity and technologies barrier of each technology, we claim that for non-strategic applications (not low background conditions), QWIP technology is the most favorite. The ternary and superlattice antimonide based materials group seems to be theoretically the best alternative, but are not recommended due to its immaturity and the high risk involved in this technology (passivation, doping control, etc.). We anticipate large penetration of the uncooled detectors to the low-end and medium-end market. The HgCdTe will still be in progress due to the inertia of the large funding and the strategic importance of this detectors technology.

Quantum well photoconductors in infrared detector technology

The paper compares the achievements of quantum well infrared photodetector (QWIP) technology with those of competitive technologies, with the emphasis on the material properties, device structure, and their impact on focal plane array (FPA) performance. Special attention is paid to two competitive technologies, QWIP and HgCdTe, in the long-wavelength IR (LWIR) and very-long-wavelength IR (VLWIR) spectral ranges. Because so far, the dialogue between the QWIP and HgCdTe communities is limited, the paper attempts to settle the main issues of both technologies. Such an approach, however, requires the presentation of fundamental limits to the different types of detectors, which is made at the beginning. To write the paper more clearly for readers, many details are included in the Appendix. In comparative studies both photon and thermal detectors are considered. Emphasis is placed on photon detectors. In this group one may distinguish HgCdTe photodiodes, InSb photodiodes, and doped silicon detectors. The potential performance of different materials as infrared detectors is examined utilizing the α/G ratio, where α is the absorption coefficient and G is the thermal generation rate. It is demonstrated that LWIR QWIP’s cannot compete with HgCdTe photodiodes as single devices, especially at higher operating temperatures (&amp;gt;70 K). This is due to the fundamental limitations associated with intersubband transitions. The advantage of HgCdTe is, however, less distinct at temperatures lower than 50 K due to problems inherent in the HgCdTe material (p-type doping, Shockley–Read recombination, trap-assisted tunneling, surface and interface instabilities). Even though QWIP is a photoconductor, several of its properties, such as high impedance, fast response time, long integration time, and low power consumption, comply well with the requirements imposed on the fabrication of large FPA’s. Due to a high material quality at low temperatures, QWIP has potential advantages over HgCdTe in the area of VLWIR FPA applications in terms of array size, uniformity, yield, and cost of the systems. The performance figures of merit of state-of-the-art QWIP and HgCdTe FPA’s are similar because the main limitations come from the readout circuits. Performance is, however, achieved with very different integration times. The choice of the best technology is therefore driven by the specific needs of a system. In the case of readout-limited detectors a low photoconductive gain increases the signal-to-noise ratio and a QWIP FPA can have a better noise equivalent difference temperature than an HgCdTe FPA with a charge well of similar size. Both HgCdTe photodiodes and QWIP’s offer multicolor capability in the MWIR and LWIR range. Powerful possibilities offered by QWIP technology are associated with VLWIR FPA applications and with multicolor detection. The intrinsic advantage of QWIP’s in this niche is due to the relative ease of growing multicolor structures with a very low defect density.

QUANTUM WELL INFRARED PHOTOCONDUCTORS IN INFRARED DETECTORS TECHNOLOGY

Investigations of the performance of quantum well infrared photodetectors (QWIPs) as compared to other types of semiconductor infrared (IR) detectors are presented. In comparative studies both photon and thermal detectors are considered. More attention is paid to photon detectors and between them we can distinguish: HgCdTe photodiodes, InSb photodiodes, Schottky barrier photoemissive detectors, and doped silicon detectors. Special attention has been paid to competitive technologies in long wavelength IR (LWIR) and very LWIR (VLWIR) spectral ranges with emphasis on the material properties, device structure, and their impact on FPA performance. The potential performance of different materials as infrared detectors is examined utilizing the α/G ratio, where α is the absorption coefficient and G is the thermal generation. From the discussion results, LWIR QWIP cannot compete with HgCdTe photodiode as the single device especially at higher temperature operation(&gt; 70 K) due to fundamental limitations associated with intersubband transitions. However, the advantage of HgCdTe is less distinct in the temperature range below 50 K due to problems involved in the HgCdTe material (p-type doping, Shockley–Read recombination, trap-assisted tunneling, surface and interface instabilities). Even though the QWIP is a photoconductor, several its properties such as high impedance, fast response time, long integration time, and low power consumption, well comply with requirements for large FPAs fabrication. Due to the high material quality at low temperature, QWIP has potential advantages over HgCdTe for VLWIR FPA applications in terms of the array size, uniformity, yield and cost of the systems. Both HgCdTe photodiodes and quantum well infrared photodetectors offer multicolor capability in the MWIR and LWIR range. Powerful possibilities of QWIP technology are connected with VLWIR FPA applications and with multicolor detection. QWIP FPAs combine the advantages of PtSi Schottky barrier arrays (high uniformity, high yield, radiation hardness, large arrays, lower cost) with the advantages of HgCdTe (high quantum efficiency and long wavelength response).

STRV-1d QWIP technology validation in space flight

New technologies are arriving on the scene that promise enhancement or new capabilities. Some of these technologies have potential for NASA and DOD space-based applications. In these cases, the technology must be demonstrated and validated to a degree that risk may be balanced for the space mission roles. Quantum well infrared photo-detector (QWIP) is one of these technologies. QWIP has a variety of space-based applications in the 8 to 16 μm wavelength range. Radiation tolerance and higher operating temperature are potentially significant benefits for long duration missions. In this paper, we describe the selection of and preparation for a mission that provides the opportunity to demonstrate and validate QWIP focal plane arrays in the natural, space radiation environment. We discuss the objectives of this demonstration opportunity, and the development and test steps required to deliver the QWIP experiment to space.

Corrugated quantum well infrared photodetectors with polyimide planarization for detector array applications

Recently, we have demonstrated a new light coupling scheme for quantum well infrared photodetectors (QWIP). The new detector structure, referred to as corrugated QWIP (C-QWIP), is created by chemically etching linear V-grooves through the detector active region. In this structure, normal incident light is directed into the detector active region through total internal reflection, with which the optical absorption of the material is increased. However, the exposed active layers have to be insulated by a dielectric material before the top metal contact can be deposited for bonding purpose. In this paper, we describe a multilayer planarization scheme using a polyimide dielectric, which is developed specifically for this detector geometry, and report the resulting detector performance. The photoresponse of the detector with linear V-grooves pattern is found to be a factor of 1.6 larger than that of a regular edge coupled detector when they are normalized to the same dark current level. No wavelength or size dependence is observed using this coupling scheme, for detector sizes ranging from 50/spl times/50 /spl mu/m/sup 2/ to 500/spl times/500 /spl mu/m/sup 2/. With these two coupling characteristics, a C-QWIP behaves as a detector with normal incident absorption, a feature that will greatly improve the manufacturability of detector arrays and can be expected to lead to widespread applications of the QWIP technology.

Comparison of the performance of quantum well and conventional bulk infrared photodetectors

Investigations of the performance of quantum well infrared photodetectors (QWIPs) as compared o other types of semiconductor infrared detectors are presented. Two types of QWIPs are considered: GaAs/AlGaAs intersubband quantum well photoconductors and type II staggered InAs/InGaSb photodiodes. In comparative studies the HgCdTe photoconductors and photodiodes, PbSnTe photodiodes, Schottky barrier photoemissive detectors and doped silicon detectors are considered. It is assumed that the performance of HgCdTe and PbSnTe photodiodes is due to thermal generation governed by the Auger mechanism in the base regions. Investigations of the fundamental physical limitations of HgCdTe photodiodes indicate better performance of this type of detectors in comparison with GaAs/AlGaAs QWIPs operated in the range 35 to 77 K. In practice however, in temperature range below 50 K the performance of the HgCdTe photodiodes is determined by trap-assited tunneling. As a result, advantage of GaAs/AlGaAs QWIPs increases in the wider spectral range (below 14 μm) and temperature below 50 K. This observation plus the maturity of GaAs/AlGaAs technology and its radiation hard characteristics promise that QWIPs technology can produce high quality focal plane arrays (FPAs) for space applications. The operating temperature for HgCdTe detectors is higher than for other types of photondetectors. HgCdTe detectors with background limited performance operate with thermoelectric coolers in the medium wavelength range, instead the long wavelength detectors operate at ≈ 100 K. HgCdTe is characterized by high absorption coefficient and quantum efficiency and relatively low thermal generation rate compared to extrinsic detectors, silicide Schottky barriers and GaAs/AlGaAs QWIPs. However, the cooling requirments for GaAs/AlGaAs QWIPs with cutoff wavelengths below 10 μm are less stringent in comparison with extrinsic detectors and Schottky barrier devices. The theoretically predicted performance of long wavelength InAs/GaInSb photodiodes are comparable with HgCdTe photodiodes. The high performance of InAs/InGaSb detectors is due to suppression of band-to-band Auger recombination rate.