This PDF file contains the front matter associated with SPIE Proceedings Volume 10177, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

The authors estimate signal-to-noise ratios (SNRs) and contrasts for both InGaAs SWIR camera (cut-off wavelength λ_co~1.7 μm) and type II superlattice (T2SL) SWIR camera (λ_co~2.3 μm), under such situations as human skin as an object and vegetation as surroundings which are illuminated only by OH night airglow. In estimating the number of signal electrons, the measured spectral properties of quantum efficiencies for both InGaAs and T2SL detectors are used along with reflectance spectra of human skin and materials, while atmospheric transmission spectra are calculated with MODTRAN. As to noise electrons, shot noise resulting from dark current of InGaAs or T2SL detector is added to photon noise and ROIC (Read-Out Integrated Circuit) noise. The SNR values for the T2SL camera are found larger than those for the InGaAs camera. The contrasts of human skin vs surroundings are positive for the T2SL camera, while those for the InGaAs camera are negative.

In recent years SCD has developed InGaAs/InP technology for Short-Wave Infrared (SWIR) imaging. The first product, Cardinal 640, has a 640×512 (VGA) format at 15μm pitch, and more than two thousand units have already been delivered to customers. Recently we have also introduced Cardinal 1280 which is an SXGA array with 10μm pitch aimed for long-range high end platforms [1]. One of the big challenges facing the SWIR technology is its proliferation to widespread low cost and low SWaP applications, specifically Low Light Level (LLL) and Image Intensifier (II) replacements. In order to achieve this goal we have invested and combined efforts in several design and development directions: 1. Optimization of the InGaAs pixel array, reducing the dark current below 2fA at 20° C in order to save TEC cooling power under harsh light and environmental conditions. 2. Design of a new "Low Noise" ROIC targeting 15e noise floor and improved active imaging capabilities 3. Design of compact, low SWaP and low cost packages. In this context we have developed 2 types of packages: a non-hermetic package with thermo-electric cooler (TEC) and a hermetic TEC-Less ceramic package. 4. Development of efficient TEC-Less algorithms for optimal imaging at both day-light and low light level conditions. The result of these combined efforts is a compact low SWaP detector that provides equivalent performance to Gen III image intensifier under starlight conditions. In this paper we will present results from lab and field experiments that will support this claim.

InAs/InAs_1-xSb_x/AlAs_1-xSb_x type-II superlattices (T2SLs) is a system of multi-interacting quantum wells. Since its introduction, this material system has drawn a lot of attention especially for infrared detection. In recent years, InAs/InAs_{1- x}Sb_x/AlAs_1-xSb_x T2SL material system has experienced incredible improvements in material quality, device structure designs and device fabrication process which elevated the performances of T2SL-based photodetectors to a comparable level to the state-of-the-art material systems for infrared detection such as Mercury Cadmium Telluride (MCT). In this paper, we will present the current status of InAs/InAs_1-xSb_x/AlAs_1-xSb_x T2SL-based photodetectors for detection in different infrared regions, from short-wavelength (SWIR) to long-wavelength (LWIR) infrared, and the future outlook of this material system.

It is numerically shown that Al/Sb free InGaAs unipolar barrier detectors with superior performance compared to the conventional heterojunction detectors can be constructed. Compositionally graded layers provide the transition between the high bandgap InGaAs barrier and the lattice matched InGaAs absorber layers. In addition, the delta doped layers remove the valence band offset in order to block only majority carriers and allow unimpeded flow of minority carriers. More than one order of magnitude reduction in the dark current is observed while photocurrent remains nearly unchanged. Proposed barrier structure utilized in this study is not limited to short wave infrared (SWIR) and can be applied to a variety of materials operating in various infrared regions.

This paper reports a 640x512 SWIR ROIC with 15um pixel pitch that is designed and fabricated using 0.18um CMOS process. Main challenge of SWIR ROIC design is related to input circuit due to pixel area and noise limitations. In this design, CTIA with single stage amplifier is utilized as input stage. The pixel design has three pixel gain options; High Gain (HG), Medium Gain (MG), and Low Gain (LG) with corresponding Full-Well-Capacities of 18.7ké, 190ké and 1.56Mé, respectively. According to extracted simulation results, 5.9é noise is achieved at HG mode and 200é is achieved at LG mode of operation. The ROIC can be programmed through an SPI interface. It supports 1, 2 and 4 output modes which enables the user to configure the detector to work at 30, 60 and 120fps frame rates. In the 4 output mode, the total power consumption of the ROIC is less than 120mW. The ROIC is powered from a 3.3V analog supply and allows for an output swing range in excess of 2V. Anti-blooming feature is added to prevent any unwanted blooming effect during readout.

For SWIR imaging applications, based on AIM’s state-of-the-art MCT IR technology specific detector designs for either low light level imaging or laser illuminated active imaging are under development. For imaging under low-light conditions a low-noise 640x512 15μm pitch ROIC with CTIA input stages and correlated double sampling was designed. The ROIC provides rolling shutter and snapshot integration. To reduce size, weight, power and cost (SWaP-C) a 640x512 format detector in a 10μm pitch is been realized. While LPE grown MCT FPAs with extended 2.5μm cut-off have been fabricated and integrated also MBE grown MCT on GaAs is considered for future production. The module makes use of the extended SWIR (eSWIR) spectral cut-off up to 2.5μm to allow combination of emissive and reflective imaging by already detecting thermal radiation in the eSWIR band. A demonstrator imager was built to allow field testing of this concept. A resulting product will be a small, compact clip-on weapon sight. For active imaging a detector module was designed providing gating capability. SWIR MCT avalanche photodiodes have been implemented and characterized on FPA level in a 640x512 15μm pitch format. The specific ROIC provides also the necessary functions for range gate control and triggering by the laser illumination. The FPAs are integrated in a compact dewar cooler configuration using AIM’s split linear cooler. A command and control electronics (CCE) provides supply voltages, biasing, clocks, control and video digitization for easy system interfacing. First lab and field tests of a gated viewing demonstrator have been carried out and the module has been further improved.

Episensors has developed a series of extended short wavelength infrared (eSWIR) cameras based on high-Cd concentration Hg_1-xCd_xTe absorbers. The cameras have a bandpass extending to 3 microns cutoff wavelength, opening new applications relative to traditional InGaAs-based cameras. Applications and uses are discussed and examples given. A liquid nitrogen pour-filled version was initially developed. This was followed by a compact Stirling-cooled version with detectors operating at 200 K. Each camera has unique sensitivity and performance characteristics. The cameras’ size, weight and power specifications are presented along with images captured with band pass filters and eSWIR sources to demonstrate spectral response beyond 1.7 microns. The soft seal Dewars of the cameras are designed for accessibility, and can be opened and modified in a standard laboratory environment. This modular approach allows user flexibility for swapping internal components such as cold filters and cold stops. The core electronics of the Stirlingcooled camera are based on a single commercial field programmable gate array (FPGA) that also performs on-board non-uniformity corrections, bad pixel replacement, and directly drives any standard HDMI display.

As material growth and processing have improved, state of the art infrared detector arrays remain limited by material properties and not processing or growth quality. In particular, the dark current can be dominated by diffusion of minority carriers in the quasineutral regions. In this work, we present a unique detector architecture that allows for dark current suppression below the fundamental diffusion limit. We have extensively studied this effect, and report dark current, photocurrent, and quantum efficiency. Finally, we conclude by offering a path to implementing this architecture into existing FPAs.

Graphene has received intensive attention in recent years because of the special physical and chemical properties. However, up to now graphene has not been widely used in optoelectronic fields yet, which is mainly caused by its semimetal properties. Therefore, changing its properties from semimetal to semiconductor is becoming a focal point. Recently, aiming at tuning the energy band of graphene, we have carried out systematic studies on the preparations of graphene based materials and devices, the CVD growth techniques of monolayer and double layer graphenes have been developed, the large-area doped graphene films have been fabricated to tune the structure-related optical and electrical properties. A novel graphene oxide (GO) preparation method namely “Tang-Lau method” has been invented, the graphene quantum dots growths by microwave assisted hydrothermal method and “Soft-Template method” have been developed, the Cl, S and K doped graphene quantum dots preparations by hydrothermal methods have also been invented. Systematic investigations have been carried out for the effect of preparation parameters on the properties of graphene based materials, the effects of size, doping elements on the energy level of graphene based materials have been explored and discussed. Based on the semiconducting graphene based materials, some novel room temperature photodetectors covering detection wavebands from UV, Vis and NIR have been designed and fabricated.

The reconnaissance capability of a military observation and targeting platform is mainly driven by the performance of the used sensors. In general, the MWIR thermal imager is the primary sensor and the use of a visible camera increases the identification capability of the platform during day for very long observation ranges. In addition to the imaging sensors a laser pointer, a laser rangefinder (LRF), and a combined laser rangefinder/ designator (LRF/D) completes the sensor suite. As LRF a single pulse eye safe rangefinder based on an OPO shifted Nd:YAG transmitter can be used. The alternative LRF/D uses an diode laser pumped dual wavelength OPO/Nd:YAG transmitter and can be operated either at 1570 nm or at 1064 nm with a pulse rate of maximum 25 pps [1].

A MWIR thermal imager [2] with a 1280x1024 MWIR detector and an optical zoom range between 1.2° and 20° horizontal fields of view provides a HD-SDI video stream in the 720p or 1080p standard. A camera build in software image stabilizer and a smart tone mapping algorithm improves the reconnaissance results for the observer.

A combined camera covers the visible, NIR and SWIR spectral range [3] using a common entrance optics. The resolution of the color camera Si-CMOS chip is 1920x1080 and of the InGaAs focal plane array it is 640x512 detector pixel. The combined VIS/NIR/SWIR camera provides improved ranging under hazy and misty atmospheric conditions and also improved detection of laser spots e.g. of the integrated laser designator with high sensitivity in the spectral range between 450 nm up to 1700 nm, most of the military lasers are operating in the NIR and SWIR spectral band [3]. The combination of the sensors in the platform improves significantly the operational use. The application of the described platform is not limited to military scout vehicles, the available sensors are also integrated in a targeting platform with similar performances but other environmental demands.

The possibilities, improvements in comparison of existing platforms and potential upgrades are discussed.

In the past decades, hyper-spectral imaging technologies were well developed in SITP, CAS. Many innovations for system design and key parts of hyper-spectral imager were finished. First airborne hyper-spectral imager operating from VNIR to TIR in the world was emerged in SITP. It is well known as OMIS(Operational Modular Imaging Spectrometer). Some new technologies were introduced to improve the performance of hyper-spectral imaging system in these years. A high spatial space-borne hyper-spectral imager aboard Tiangong-1 spacecraft was launched on Sep.29, 2011. Thanks for ground motion compensation and high optical efficiency prismatic spectrometer, a large amount of hyper-spectral imagery with high sensitivity and good quality were acquired in the past years. Some important phenomena were observed. To diminish spectral distortion and expand field of view, new type of prismatic imaging spectrometer based curved prism were proposed by SITP. A prototype of hyper-spectral imager based spherical fused silica prism were manufactured, which can operate from 400nm~2500nm. We also made progress in the development of LWIR hyper-spectral imaging technology. Compact and low F number LWIR imaging spectrometer was designed, manufactured and integrated. The spectrometer operated in a cryogenically-cooled vacuum box for background radiation restraint. The system performed well during flight experiment in an airborne platform. Thanks high sensitivity FPA and high performance optics, spatial resolution and spectral resolution and SNR of system are improved enormously. However, more work should be done for high radiometric accuracy in the future.

Pacific Advanced Technology (PAT) has developed an infrared hyperspectral camera, both MWIR and LWIR, small enough to serve as a payload on a miniature unmanned aerial vehicles. The optical system has been integrated into the cold-shield of the sensor enabling the small size and weight of the sensor. This new and innovative approach to infrared hyperspectral imaging spectrometer uses micro-optics and will be explained in this paper. The micro-optics are made up of an area array of diffractive optical elements where each element is tuned to image a different spectral region on a common focal plane array. The lenslet array is embedded in the cold-shield of the sensor and actuated with a miniature piezo-electric motor. This approach enables rapid infrared spectral imaging with multiple spectral images collected and processed simultaneously each frame of the camera. This paper will present our optical mechanical design approach which results in an infrared hyper-spectral imaging system that is small enough for a payload on a mini-UAV or commercial quadcopter. Also, an example of how this technology can easily be used to quantify a hydrocarbon gas leak’s volume and mass flowrates. The diffractive optical elements used in the lenslet array are blazed gratings where each lenslet is tuned for a different spectral bandpass. The lenslets are configured in an area array placed a few millimeters above the focal plane and embedded in the cold-shield to reduce the background signal normally associated with the optics. We have developed various systems using a different number of lenslets in the area array. Depending on the size of the focal plane and the diameter of the lenslet array will determine the spatial resolution. A 2 x 2 lenslet array will image four different spectral images of the scene each frame and when coupled with a 512 x 512 focal plane array will give spatial resolution of 256 x 256 pixel each spectral image. Another system that we developed uses a 4 x 4 lenslet array on a 1024 x 1024 pixel element focal plane array which gives 16 spectral images of 256 x 256 pixel resolution each frame.

Hyperspectral imaging (HSI) in the Mid-Wave InfraRed (MWIR, 3-5 microns) can provide information on a variety of science applications from determining the chemical composition of lava lakes on Jupiter’s moon Io, to investigating the amount of carbon liberated into the Earth’s atmosphere during a wildfire. The limited signal available in the MWIR presents technical challenges to achieving high signal-to-noise ratios, and therefore it is typically necessary to cryogenically cool MWIR instruments. With recent improvements in microbolometer technology and emerging interferometric techniques, we have shown that uncooled microbolometers coupled with a Sagnac interferometer can achieve high signal-to-noise ratios for long-wave infrared HSI. To explore if this technique can be applied to the MWIR, this project, with funding from NASA, has built the Miniaturized Infrared Detector of Atmospheric Species (MIDAS). Standard characterization tests are used to compare MIDAS against a cryogenically cooled photon detector to evaluate the MIDAS instruments’ ability to quantify gas concentrations. Atmospheric radiative transfer codes are in development to explore the limitations of MIDAS and identify the range of science objectives that MIDAS will most likely excel at. We will simulate science applications with gas cells filled with varying gas concentrations and varying source temperatures to verify our results from lab characterization and our atmospheric modeling code.

Infrared sounders measure the upwelling radiation of the Earth in the Midwave Infrared (MWIR) and Longwave Infrared (LWIR) region of the spectrum with global daily coverage from space. The observed radiances are assimilated into weather forecast models and used to retrieve lower tropospheric temperature and water vapor for climate studies. There are several operational sounders today including the Atmospheric Infrared Sounder (AIRS) on Aqua, the Crosstrack Infrared Sounder (CrIS) on Suomi NPP and JPSS, and the Infrared Atmospheric Sounding Interferometer (IASI) on the MetOp spacecraft. The CubeSat Infrared Atmospheric Sounder (CIRAS) is a NASA In-flight Validation of Earth Science Technologies (InVEST) program to demonstrate three new instrument technologies in an imaging sounder configuration. The first is a 2D array of High Operating Temperature Barrier Infrared Detector (HOT-BIRD) material, selected for its high uniformity, low cost, low noise and higher operating temperatures than traditional materials. The detectors are hybridized to a commercial ROIC and commercial camera electronics. The second technology is a MWIR Grating Spectrometer (MGS) designed to provide imaging spectroscopy for atmospheric sounding in a CubeSat volume. The MGS employs an immersion grating or grism, has no moving parts, and is based on heritage spectrometers including the OCO- 2. The third technology is a Black Silicon infrared blackbody calibration target. The Black Silicon offers very low reflectance over a broad spectral range on a flat surface and is more robust than carbon nanotubes. JPL will also develop the mechanical, electronic and thermal subsystems for the CIRAS payload. The spacecraft will be a commercially available CubeSat. The integrated system will be a complete 6U CubeSat capable of measuring temperature and water vapor profiles with good lower tropospheric sensitivity. The low cost of CIRAS enables multiple units to be flown to improve temporal coverage or measure 3D Atmospheric Motion Vector (AMV) winds. CIRAS will launch in 2019 and is only a technology demonstration. However, what we learn will benefit future instruments that support operational weather forecasting and climate studies.

We provide a brief overview of recent progress in III-V semiconductor infrared photodetectors resulting from advances in infrared detector materials, including type-II superlattices (T2SL) and InAsSb alloy, and the unipolar detector architecture. We summarize T2SL unipolar barrier infrared detector and focal plane array development at the NASA Jet Propulsion Laboratory in support of the Vital Infrared Sensor Technology Acceleration (VISTA) Program. We also comment on the connection of T2SL barrier infrared detector to MCT infrared detectors.

Recent advances in superlattice-based infrared detectors have rendered this material system a solid alternative to HgCdTe for dual-band sensing applications. In particular, superlattices are attractive from a manufacturing perspective as the epitaxial wafers can be grown with a high degree of lateral uniformity, low macroscopic defect densities (< 50 cm^-2) and achieve dark current levels comparable to HgCdTe detectors. In this paper, we will describe our recent effort on the VISTA program towards producing HD-format (1280x720, 12 μm pitch) superlattice based, dual-band MWIR/LWIR FPAs. We will report results from several multi-wafer fabrication lots of 1280x720, 12 μm pitch FPAs processed over the last two years. To assess the FPA performance, noise equivalent temperature difference (NETD) measurements were conducted at 80K, f/4.21 and using a blackbody range of 22°C to 32°C. For the MWIR band, the NETD was 27.44 mK with a 3x median NETD operability of 99.40%. For the LWIR band, the median NETD was 27.62 mK with a 3x median operability of 99.09%. Over the course of the VISTA program, HRL fabricated over 30 FPAs with similar NETDs and operabilities in excess of 99% for both bands, demonstrating the manufacturability and high uniformity of III-V superlattices. We will also present additional characterization results including blinkers, spatial stability, modulation transfer function and thermal cycles reliability.

Barrier detectors based on III-V materials have recently been developed to realize substantial improvements in the performance of mid-wave infrared (MWIR) detectors, enabling FPA performance at high operating temperatures. The relative ease of processing the III-V materials into large-format, small-pitch FPAs offers a cost-effective solution for tactical imaging applications in the MWIR band as an attractive alternative to HgCdTe detectors. In addition, small pixel (5-10μm pitch) detector technology enables a reduction in size of the system components, from the detector and ROIC chips to the focal length of the optics and lens size, resulting in an overall compactness of the sensor package, cooling and associated electronics. To exploit the substantial cost advantages, scalability to larger format (2kx2k/10μm) and superior wafer quality of large-area GaAs substrates, we have fabricated antimony based III-V bulk detectors that were metamorphically grown by MBE on GaAs substrates. The electro-optical characterization of fabricated 2kx2k/10μm FPAs shows low median dark current (3 x 10^-5 A/cm² with λ_co = 5.11μm or 2.2 x 10^-6 A/cm² with λ_co = 4.6μm) at 150K, high NEdT operability (3x median value) >99.8% and >60% quantum efficiency (non-ARC). In addition, we report our initial result in developing small pixel (5μm pitch), high definition (HD) MWIR detector technology based on superlattice III-V absorbing layers grown by MBE on GaSb substrates. The FPA radiometric result is showing low median dark current (6.3 x 10^-6 A/cm² at 150K with λ_co = 5.0μm) with ~50% quantum efficiency (non-ARC), and low NEdT of 20mK (with averaging) at 150K. The detector and FPA test results that validate the viability of Sb-based bulk and superlattice high operating temperature MWIR FPA technology will be discussed during the presentation.

Photodetectors in the non-visible region of the electromagnetic spectrum are essential for security, defense and space science as well as industrial and scientific applications. The research activities at Fraunhofer IAF cover a broad range in the infrared (IR) regime. Whereas short-wavelength IR (SWIR, <1.7 μm) detectors are realized by InGaAs/InP structures, InAs/GaSb type-II superlattice (T2SL) infrared detectors are developed for the spectral bands from mid- (MWIR, 3-5 μm) to long-wavelength IR (LWIR, 8-12 μm). We report on the extension of the superlattice empirical pseudopotential method (SEPM) to 300 K for the design of LWIR heterostructures for operation near room temperature. Recently, we have also adapted heterostructure concepts to our well established bi-spectral T2SL MWIR detector resulting in a dark current density below 2 × 10^-9 A/cm² for a cut-off wavelength close to 5 μm. Finally, we present first results obtained with a gated viewing system based on our InGaAs/InAlAs/InP avalanche photodiode arrays.

Type-II strained layer superlattices (SLS) are an active research topic in the infrared detector community and applications for SLS detectors continue to grow. SLS detector technology has already reached the commercial market due to improvements in material quality, device design, and device fabrication. Despite this progress, the optimal superlattice design has not been established, and at various times has been believed to be InAs/GaSb, InAs/InGaSb, or InAs/InAsSb. Building on these, we investigate the properties of a new mid-wave infrared SLS material: InGaAs/InAsSb SLS. The ternary InGaAs/InAsSb SLS has three main advantages over other SLS designs: greater support for strain compensation, enhanced absorption due to increased electron-hole wavefunction overlap, and improved vertical hole mobility due to reduced hole effective mass. Here, we compare three ternary SLSs, with approximately the same bandgap (0.240 eV at 150 K), comprised of Ga fractions of 5%, 10%, and 20% to a reference sample with 0% Ga. Enhanced absorption is both theoretically predicted and experimentally realized. Furthermore, the characteristics of ternary SLS infrared detectors based on an nBn architecture are reported and exhibit nearly state-of-the-art dark current performance with minimal growth optimization. We report standard material and device characterization information, including dark current and external quantum efficiency, and provide further analysis that indicates improved quantum efficiency and vertical hole mobility. Finally, a 320×256 focal plane array built based on the In_0.8Ga_0.2As/InAs_0.65Sb_0.35 SLS design is demonstrated with promising performance.

Development towards higher operating temperature, smaller pitch and larger format arrays is ongoing for midwave (MW) InAs/GaSb superlattice detectors at IRnova. One part of this effort entails improvement in the MW detector design, which has resulted in increased quantum efficiency to 55-60 % in the entire 3-5 μm wavelength region, with dark current levels lower than 3×10^-6 A/cm² at 120 K. Furthermore, MW-MW dual band detectors have been realized by using pixel filters fabricated on top of regular MW FPAs. The pixel filters were designed to transmit infrared radiation in the 3.5 μm - 4.1 μm wavelength region and to completely block light shorter than 3.5 μm. By comparing the signals of filtered and unfiltered pixels, excellent contrast between the two bands were obtained. Long wave infrared detectors have also been realized with cut-off wavelength at 12.2 μm and dark current levels following the Rule07 trendline from 80 K to 160 K, with only two times higher dark current than Rule07 at 80 K.

One of JAXA’s future missions, using an imaging Fourier Transform Spectrometer (FTS), requires the focal plane array (FPA) that has high sensitivity up to the very long-wavelength infrared (VLWIR) region. Since a Type-II superlattice (T2SL) is the only known infrared material to exhibit performance that is theoretically predicted to be higher than that of HgCdTe additionally the cutoff wavelength can be tailored in the wavelength region of 3-30 μm, we started the research and development of the T2SL detector in 2009. In order to confirm our final goal, which is to realize the FPA with a cutoff wavelength of 15 μm, we first fabricated the 320 × 256 (QVGA format) InAs/GaInSb T2SL FPA with a cutoff wavelength of 15 μm, and the large-format 640 × 512 (VGA format) T2SL FPA is followed because the other missions, using an infrared imager, require the large-format FPA. The noise-equivalent delta temperature measured with F1.4 optics was 0.15 K for QVGA format T2SL FPA at 77 K. It was 0.35 K for VGA format T2SL FPA at 77 K, but there is non-uniformity, and further improvements are necessary to achieve high performance FPAs.

The requirement of the infrared technology applied on meteorological satellites is the key driving force for the development of infrared technology in Shanghai institute of technical physics (SITP), Chinese Academy of Sciences. The meteorological satellites have become a main detection method for the weather and ocean observation, there are totally 15 meteorological satellites that were launched into both sun synchronous and geostationary orbit and more satellites are under construction to be the second generation ones. The infrared remote sensors are the main payloads on-board on all these satellites. By these infrared remote sensors one can obtain the remote sensing data for ocean colour, water vapour, weather forecasting, and get the atmospheric temperature profile and humidity profile, etc. As the key technology in the infrared remote sensor, the infrared detector technology is developed mainly using the HgCdTe material, meanwhile the quantum well infrared photodetector and type II super-lattice infrared detector are also developed.

Cadmium Zinc Telluride (Cd_1-xZn_xTe or CZT) is a compound semiconductor substrate material that has been used for infrared detector (IR) applications for many years. CZT is a perfect substrate for the epitaxial growth of Mercury Cadmium Telluride (Hg_1-xCd_xTe or MCT) epitaxial layers and remains the material of choice for many high performance IR detectors and focal plane arrays that are used to detect across wide IR spectral bands. Critical to the fabrication of high performance MCT IR detectors is a high quality starting CZT substrate, this being a key determinant of epitaxial layer crystallinity, defectivity and ultimately device electro-optical performance. In this work we report on a new source of substrates suitable for IR detector applications, grown using the Travelling Heater Method (THM). This proven method of crystal growth has been used to manufacture high quality IR specification CZT substrates where industry requirements for IR transmission, dislocations, tellurium precipitates and copper impurity levels have been met. Results will be presented for the chemo-mechanical (CMP) polishing of CZT substrates using production tool sets that are identical to those that are used to produce epitaxy-ready surface finishes on related IR compound semiconductor materials such as GaSb and InSb. We will also discuss the requirements to scale CZT substrate manufacture and how with a new III-V like approach to both CZT crystal growth and substrate polishing, we can move towards a more standardized product and one that can ultimately deliver a standard round CZT substrate, as is the case for competing IR materials such as GaSb, InSb and InP.

GaSb and its heterostructures grown by molecular beam epitaxy (MBE) have received much attention given their application in a wide range of mid-wave and long-wave IR photodetector applications. With the maturation of the MBE growth process, focus is now turned to improving manufacturing readiness and the transition to the production of large-format wafers. We will discuss the transition from the development of early detector layer structures on 2” diameter GaSb substrates, through today’s 3”/4” production standard, and to the onset of 5” pilot production from the perspective of volume compound semiconductor manufacturing. We will report on the growth of 5” GaSb-based MWIR nBn detector structures using a large format 5×5” production MBE platform. Structural and optical properties, as well as electrical data from large-area mesa diodes will be presented and compared with results achieved with smaller batch size MBE reactor platform.

Theoretical and experimental investigations on the response time improvement of biased and unbiased long-wave infrared (LWIR) HgCdTe detectors operating at temperatures T = 230K were presented in this paper. MOCVD technology is an excellent tool in fabrication of different HgCdTe detector structures with a wide range of composition, donor/acceptor doping and without post grown ex-situ annealing. Donor doping efficiency in (111) and (100) oriented HgCdTe layers has been discussed. The time constant is lower in biased detectors due to Auger suppression phenomena and reduction of diffusion capacitance related to wider depletion region. The relatively high bias currents requirements and excessive low frequency noise which reduces the detectivity of biased detectors inspire researches on the time constant improvement of unbiased detectors. The response time of high-operating temperature (HOT) LWIR HgCdTe detectors revealed complex behavior being dependent on the applied the reverse bias, the operating temperature, the absorber thickness and doping, the series resistance and the electrical area of the devices.

Size, weight and power (SWaP) reduction is highly desired by applications such as sights for the dismounted soldier or small gimbals for UAVs. But why have high performance and small size of IR systems inevitably exclude each other? Namely, recent development progress in the fields of miniature cryocoolers, short dewars and high operating temperature (HOT) FPAs combined with pitch size reduction opens the door for very compact MWIR-modules while keeping high electro-optical performance.

Now, AIM has realized first prototypes of an ultra-compact high-performance MWIR engine in a total volume of only 18cl (60mm length x 60mm height x 50mm width). Impressive SWaP characteristics are completed by a total weight below 400g and a power consumption < 4W in basic imaging mode. The engine consists of a XGA-format (1024x768) MCT detector array with 10μm pitch and a low power consuming ROIC. It is cooled down to a typical operating temperature of ~160K by the miniature linear cryocooler SX020. The dewar uses a short coldfinger and is designed to reduce the heat load as much as possible. The cooler drive electronics is implemented in the CCE layout in order to reduce the required space of the printed boards and to save power. Uncorrected 14bit video data is provided via Camera Link. Optionally, a small image processing board can be stacked on top of the CCE to gain access to basic functions such as BPR, 2- point NUC and dynamic reduction. This paper will present the design, functionalities and performance data of the ultra-compact MCT MWIR engine operated at HOT.

The present article deals with device physics and modeling of an Hg_0.28Cd_0.72Te wide-area electron-initiated avalanche photodiode, with main input data extracted from first principles electronic structure codes. Due to the large dimensions of 30 μm x 30 μm x 11 μm a method which combines Monte Carlo transport simulation in the active multiplication layer with ‘weak conduction’ modeling in the charge carrier exit paths is introduced. Consequences resulting from adding perturbative, non-self-consistent small-signal analyses upon a self-consistent, large-signal background bias simulation are briefly examined. Likewise, the issue of ambipolar versus independent electron-hole transport in the absorption layer is discussed. We investigate the effects of alloy scattering on avalanche gain and compare alloy scattering rates used in some recent studies. Alloy scattering is for this particular device and model shown to increase the gain by more than an order of magnitude at typical bias voltages.

The CdZnTe-based and GaAs-based HgCdTe epilayers were grown by liquid phase epitaxy and molecular beam epitaxy, respectively, and then coated by CdTe layers as barrier cap layers for ion implantation. Subsequently, arsenic ions were implanted into the samples at different implant energies, and the two-step high temperature annealing under Hg overpressure was operated on as-implanted samples to eliminate induced damages and activate arsenic ions. After thinning the as-implanted and annealed samples by ion milling, the microstructure of lattice defects in arsenic-implanted and annealed HgCdTe was characterized by high resolution transmission electron microscopy (HRTEM), while the arsenic profiles were measured by secondary ion mass spectroscopy (SIMS). By X-ray diffraction (XRD), the influences of pre-annealing, ion implantation and post-annealing on lattice structure were studied. The experimental results indicate that the implant induced defects underneath the amorphized layer contain dislocation clusters and dislocation lines. For the implant energy of 450keV, a residual point defect belt was observed around the previous amorphous/crystal (a/c) interface in the as-implanted sample after annealing, implying that the recrystallization occurs from surface towards a/c interface. The HRTEM observation of the point defect shows that the defect is a cluster of vacancies in fact. Also, the ion implantation not only broadens the XRD peak, but also makes the peak deviation and split. It indicates that the introduction of atomic stress changes the lattice constant, thereby leading to the peak deviation.

Multicolor detection capabilities, which bring information on the thermal and chemical composition of the scene, are desirable for advanced infrared (IR) imaging systems. This communication reviews intra and multiband solutions developed at CEA-Leti, from dual-band molecular beam epitaxy grown Mercury Cadmium Telluride (MCT) photodiodes to plasmon-enhanced multicolor IR detectors and backside pixelated filters. Spectral responses, quantum efficiency and detector noise performances, pros and cons regarding global system are discussed in regards to technology maturity, pixel pitch reduction, and affordability. From MWIR-LWIR large band to intra MWIR or LWIR bands peaked detection, results underline the full possibility developed at CEA-Leti.

SOFRADIR is the worldwide leader on the cooled IR detector market for high-performance space, military and security applications thanks to a well mastered Mercury Cadmium Telluride (MCT) technology, and recently thanks to the acquisition of III-V technology: InSb, InGaAs, and QWIP quantum detectors. As a result, strong and continuous development efforts are deployed to deliver cutting edge products with improved performances in terms of spatial and thermal resolution, dark current, quantum efficiency, low excess noise and high operability. The actual trend in quantum IR detector development is the design of very small pixel, with the higher achievable operating temperature whatever the spectral band. Moreover maintaining the detector operability and image quality at higher temperature moreover for long wavelength is a major issue. This paper presents the recent developments achieved at Sofradir to meet this challenge for LW band MCT extrinsic p on n technology with a cut-off wavelength of 9.3μm at 90K. State of the art performances will be presented in terms of dark current, operability and NETD temperature dependency, quantum efficiency, MTF, and RFPN (Residual Fixed Pattern Noise) stability up to 100K.

This paper discusses postponement strategy applied to the Daphnis 10μm products family designed on purpose for postponement and for performing late-stage product completion as close to demands as possible. Regarding individual building blocks, DAPHNIS generic parts are created during the initial stages of the manufacturing process. In the later stages, these generic parts are customized to create the final product.

High performance multi-layer MWIR HgCdTe detector design requires detailed analysis considering the interaction between layers and the nonlinear effects. For this purpose, an in-house numerical model is utilized so that electrical and optical parameters are manipulated to eliminate the undesired performance limits. An ideal detector with perfect crystal quality is expected to have diffusion limited dark current. However, for low operating temperatures (<120K), which is usually the case for the high performance applications, SRH mechanism may dominate dark current especially for alternative substrate detectors and low crystal quality resulting in a short SRH lifetime (~200ns). Here, physical sizes, composition and doping profiles are optimized to suppress generation-recombination (GR) dark current so that cooling burden can be minimized. We numerically achieve ~30K (from ~85K to ~115K) increase on the operating temperature without degrading the system performance parameters for the detection of near room temperature object (300K) by placing a wide bandgap layer inside the bandgap.

There has been a growing demand over the past few years for infrared detectors with a smaller pixel dimension. On the one hand, this trend of pixel shrinkage enables the overall size of a given Focal Plan Array (FPA) to be reduced, allowing the production of more compact, lower power, and lower cost electro-optical (EO) systems. On the other hand, it enables a higher image resolution for a given FPA area, which is especially suitable in infrared systems with a large format that are used with a wide Field of View (FOV). In response to these market trends SCD has developed the Blackbird family of 10 μm pitch MWIR digital infrared detectors. The Blackbird family is based on three different Read- Out Integrated Circuit (ROIC) formats: 1920×1536, 1280×1024 and 640×512, which exploit advanced and mature 0.18 μm CMOS technology and exhibit high functionality with relatively low power consumption. Two types of 10 μm pixel sensing arrays are supported. The first is an InSb photodiode array based on SCD's mature planar implanted p-n junction technology, which covers the full MWIR band, and is designed to operate at 77K. The second type of sensing array covers the blue part of the MWIR band and uses the patented XBn-InAsSb barrier detector technology that provides electro-optical performance equivalent to planar InSb but at operating temperatures as high as 150 K. The XBn detector is therefore ideal for low Size, Weight and Power (SWaP) applications. Both sensing arrays, InSb and XBn, are Flip-chip bonded to the ROICs and assembled into custom designed Dewars that can withstand harsh environmental conditions while minimizing the detector heat load. A dedicated proximity electronics board provides power supplies and timing to the ROIC and enables communication and video output to the system. Together with a wide range of cryogenic coolers, a high flexibility of housing designs and various modes of operation, the Blackbird family of detectors presents solutions for EO systems which cover both the very high-end and the low SWaP types of application. In this work we present in detail the EO performance of the Blackbird detector family.

We describe our recent results in developing and maturing small pixel (5μm pitch), high definition (HD) mid-wave infrared (MWIR) detector technology as well as focal-plane-array (FPA) hybrids, and prototype 2.4 Megapixel camera development operating at high temperature with low dark current and high operability. Advances in detector performance over the last several years have enabled III-V high operating temperature (T≥150K), unipolar detectors to emerge as an attractive alternative to HgCdTe detectors. The relative ease of processing the materials into large-format, small-pitch FPAs offers a cost-effective solution for tactical imaging applications in the MWIR band. In addition, small pixel detector technology enables a reduction in size of the system components, from the detector and ROIC chips to the focal length of the optics and lens size, resulting in an overall compactness of the sensor package, cooling and associated electronics. An MBE system has been used to grow antimony-based detector structures with 5.1μm cutoff with low total thickness variation (TTV) across a 3” wafer, in order to realize high interconnect yield for small-pitch FPAs. A unique indium bump scheme is proposed to realize 5μm pitch arrays with high connectivity yield. Several 1kx2k /5μm hybrids have been fabricated using Cyan’s CS3 ROICs with proper backend processing and finally packaged into a portable Dewar camera. The FPA radiometric result is showing low median dark current of 2.3x10^-5 A/cm² with > 99.9% operability, and >60% QE (without AR coating).

For about 30 years, AIM has been ranking among the leading global suppliers for high-performance MCT infrared detectors, with its portfolio spanning the photosensitivity cut-off range from the SWIR to the VLWIR and from 1st generation to 3rd generation FPA devices. To meet the market demands for SWaP-C- and IR-detectors with additional functionalities such as multicolor detection, AIM employs both LPE and MBE technology.

From AIM´s line of highest-performance single color detectors fabricated by LPE, we will present our latest excellent results of 5.3 μm cut-off MWIR MCT detectors with 1024x768 pixels and a 10 μm pixel pitch. AIM’s powerful low dark current LWIR and VLWIR p-on-n device technology on LPE-grown MCT has now been extended to the MWIR spectral range. A comparison of results from n-on-p and p-on-n MWIR MCT planar photodiode arrays is presented. Operating temperatures of 160 K and higher, in conjunction with low defect density and excellent thermal sensitivity (NETD) are attained. The results achieved for LPE MWIR are compared to MBE MWIR data.

For both the cost-efficient production of MWIR single color MCT detectors, as well as 3rd generation multicolor MCT detectors, AIM makes use of MBE growth of MCT on large-area GaAs substrates. The now-available AIM MWIR single color MBE MCT detectors grown on GaAs are qualified, delivered, and have reached a maturity fully meeting customers’ requirements. Representing AIM’s multicolor detector development, latest test results on a 640x512 pixels with a 20 μm pitch design will be presented. The MWIR/MWIR diodes demonstrate high QE, very low color cross talk, and excellent NETD in conjunction with low defect densities.

Mid-wavelength infrared photodetectors incorporated into a unipolar barrier architecture with a bulk InAs_xSb_1-x absorber and an AlSb barrier layer are demonstrated. An extended cutoff was achieved by increasing the lattice constant from 6.09 Å of the GaSb substrate to 6.13 Å using a 1.5 μm thick AlSb buffer layer. This enabled the growth of bulk absorber material with a higher antimony content, InAs_0.81Sb_0.19, and a greater than 5 μm cutoff. Transitioning the lattice to 6.13 Å also enabled the implementation of a simple binary AlSb layer as a unipolar barrier to block majority carrier electrons and reduce dark current noise. Individual test devices with 4 μm thick absorbers displayed 150 K dark current density, cutoff wavelength, quantum efficiency, and specific detectivity of 3 x 10^-5 A/cm², 5.31 μm, 44 % at 3.4 μm, and 4.3 x 10¹¹ cmHz^1/2/W at 5 μm, respectively. The instantaneous dark current activation energy at a given bias and temperature was determined via Arrhenius analysis from the dark current vs. temperature and bias data, and a discussion of valence band alignment between the InAs_xSb_1-x absorber and AlSb barrier layers is presented. The carrier concentration, mobility, and lifetime of the bulk absorber material and the device performance will be presented and a discussed.

We report high quantum efficiency (QE) MWIR barrier photodetectors based on the InAs/GaSb/AlSb type II superlattice (T2SL) material system. The nBp design consists of a single unipolar barrier (InAs/AlSb SL) placed between a 4 μm thick p-doped absorber (InAs/GaSb SL) and an n-type contact layer (InAs/GaSb SL). At 80K, the device exhibited a 50% cut-off wavelength of 5 μm, was fully turned-ON at zero bias and the measured QE was 62% (front side illumination with no AR coating) at 4.5 μm with a dark current density of 8.5×10-9 A/cm² . At 150 K and Vb=50 mV, the 50% cut-off wavelength increased to 5.3 μm and the quantum efficiency (QE) was measured to be 64% at 4.5 μm with a dark current of 1.07×10-⁴ A/cm² . The measurements were verified at multiple AFRL laboratories. The results from this device along with the analysis will be presented in this paper.

In this work, we have proposed a model for the ultimate physical limit on the sensitivity of the heterojunction bipolar phototransistors (HPTs). Based on our modeling we have extracted the design criteria for the HPT for high sensitivity application. HPT with the submicron emitter and base area has the potential to be used for the low number photon resolving in near-infrared (NIR) wavelength. However, in practice, the quality of materials, processing, and the passivation plays an important role in the realization of the highly sensitive HPT. For short wave infrared (SWIR) HPTs based on lattice matched InGaAs to InP is studied. For these devices, conditions to reach to the highest possible sensitivity is examined. We have made an HPT based on InGaAs collector and base on the InP substrate. After developing proper processing combination of wet and dry etching and the surface passivation for the device we made an imager with 320x256 pixels based with a 30m pixel pitch. The imager shows the sensitivity less the 30 photons for each pixel with the frame rate more than 1K frames per second.

Recently we have demonstrated a novel method of extending the cut-off wavelength of InAsSb nBn detectors, by incorporating a series of monolayers of InSb. Here we study photoluminescence and minority carrier lifetime of this InAsSb/InSb digital alloy. While increasing temperature from 15 K to 40 K we show a 14 meV blue shift of the photoluminescence peak energy and a decrease in lifetime. This deviation from the expected Varshni empirical relation indicates strong carrier localization. We contrast to photoluminescence and lifetime results in bulk InAsSb. We discuss implications of this localization for design of digital alloy InAsSb/InSb nBn detectors.

The conventional processing of the III-V nBn photodetectors defines mesa devices by etching the contact n-layer and stopping immediately above the barrier, i.e., a shallow etch. This processing enables great suppression of surface leakage currents without having to explore surface passivation techniques. However, devices that are made with this processing scheme are subject to lateral diffusion currents. To address the lateral diffusion current, we compare the effects of different processing approaches and epitaxial structures of nBn detectors. The conventional solution for eliminating lateral diffusion current, a deep etch through the barrier and the absorber, creates increased dark currents and an increased device failure rate. To avoid deep etch processing, a new device structure is proposed, the inverted-nBn structure. By comparing with the conventional nBn structure, the results show that the lateral diffusion current is effectively eliminated in the inverted-nBn structure without elevating the dark currents.

This paper reports on the development of a fully packaged focal plane array of broadband microbolometers. The detector makes use of a gold black thin film to expand its absorption range from 3 to 14 μm. A low temperature packaging process was developed to minimize sintering of the gold black absorber during vacuum sealing of the bolometer array package. The gold black absorber was also laser trimmed to prevent lateral diffusion of heat and promote a better MTF. The resulting FPAs show a NETD lower than 25 mK at a frame rate of 50 Hz

Infrared (IR) polarimetric imaging is a promising approach to enhance object recognition with conventional IR imaging for applications such as artificial object recognition from the natural environment and facial recognition. However, typical infrared polarimetric imaging requires the attachment of polarizers to an IR camera or sensor, which leads to high cost and lower performance caused by their own IR radiation. We have developed asymmetric mushroom plasmonic metamaterial absorbers (A-MPMAs) to address this challenge. The A-MPMAs have an all-Al construction that consists of micropatches and a reflector layer connected with hollow rectangular posts. The asymmetric-shaped micropatches lead to strong polarization-selective IR absorption due to localized surface plasmon resonance at the micropatches. The operating wavelength region can be controlled mainly by the micropatch and the hollow rectangular post size. AMPMAs are complicated three-dimensional structures, the fabrication of which is challenging. Hollow rectangular post structures are introduced to enable simple fabrication using conventional surface micromachining techniques, such as sacrificial layer etching, with no degradation of the optical properties. The A-MPMAs have a smaller thermal mass than metal-insulator-metal based metamaterials and no influence of the strong non-linear dispersion relation of the insulator materials constant, which produces a gap in the wavelength region and additional absorption insensitive to polarization. A-MPMAs are therefore promising candidates for uncooled IR polarimetric image sensors in terms of both their optical properties and ease of fabrication. The results presented here are expected to contribute to the development of highperformance polarimetric uncooled IR image sensors that do not require polarizers.

Low dimensional semiconductors have attracted enormous attention in recent years. Owing to the special dimension confinement, photodetectors based on low dimensional materials and their hybrid systems exhibit considerable performance at room temperature. This differs from traditional thin-film infrared photodetectors which require liquid nitrogen cooling. In this paper, we introduce uncooled photodetectors based on one dimensional (1D) nanowires, two-dimensional (2D) materials, 2D hybrid structures and 1D/2D heterostructures. We illustrate their working mechanisms and reveal the potential for practical infrared detection.

A prototype of a readout IC (ROIC) designed for use in high temperature coefficient of resistance (TCR) SiGe microbolometers is presented. The prototype ROIC architecture implemented is based on a bridge with active and blind bolometer pixels with a capacitive transimpedance amplifier (CTIA) input stage and column parallel integration with serial readout. The ROIC is designed for use in high (≥ 4 %/K) TCR and high detector resistance Si/SiGe microbolometers with 17x17 μm² pixel sizes in development. The prototype has been designed and fabricated in 0.25- μm SiGe:C BiCMOS process.

Hyperspectral imaging (HSI) is a technique with a growing list of applications and potential users, as this technique combines the power of imaging with the chemical discrimination of spectroscopy. Because HSI divides light from the scene into narrow slices of wavelength, the technique is typically thought to require cryogenic arrays to achieve the ultimate sensitivity. However, within the last two decades microbolometer arrays have improved in sensitivity, pixel count and total array area. In Hawai’i we have shown that microbolometer arrays can provide sufficient sensitivities for a variety of infrared HSI applications. The ability of microbolometer arrays to operate at ambient-temperature make them attractive candidates for low power applications, including space-based instruments on small satellites. We have two NASA projects to determine the suitability of uncooled microbolometers for HSI systems with the aim of HSI measurements from smaller satellites than is possible with cryogenic instruments. The suitability of a detector is governed in part by its spectral response. Microbolometers have wide variations in spectral response by technology and vendor, as part of our NASA projects we are conducting a spectral response measurement campaign on five different microbolometer cameras. Three of the cameras are sensitive to the long-wave infrared from 7.5 to 14 microns (two FLIR cameras and a Sofradir camera), one to the mid-wave infrared from 3 to 5 microns (LumaSense camera), and the last is sensitive to both regions from 3 to 14 microns (INO camera). Results from this campaign will be presented.

A 32x32 prototype of a digital readout IC (DROIC) for medium-wave infrared focal plane arrays (MWIR IR-FPAs) is presented. The DROIC employs in-pixel photocurrent to digital conversion based on a pulse frequency modulation (PFM) loop and boasts a novel feature of off-pixel residue conversion using 10-bit column SAR ADCs. The remaining charge at the end of integration in typical PFM based digital pixel sensors is usually wasted. Previous works employing in-pixel extended counting methods make use of extra memory and counters to convert this left-over charge to digital, thereby performing fine conversion of the incident photocurrent. This results in a low quantization noise and hence keeps the readout noise low. However, focal plane arrays (FPAs) with small pixel pitch are constrained in pixel area, which makes it difficult to benefit from in-pixel extended counting circuitry. Thus, in this work, a novel approach to measure the residue outside the pixel using column -parallel SAR ADCs has been proposed. Moreover, a modified version of the conventional PFM based pixel has been designed to help hold the residue charge and buffer it to the column ADC. In addition to the 2D array of pixels, the prototype consists of 32 SAR ADCs, a timing controller block and a memory block to buffer the residue data coming out of the ADCs. The prototype has been designed and fabricated in 90nm CMOS.

A 15 μm pixel pitch 640×512 Readout Circuit (ROIC) for MWIR applications is designed and fabricated using 0.18 um CMOS process. The ROIC is implemented using Direct Injection (DI) input stage with programmable pixel gain where maximum full-well-capacity (FWC) is more than 13Mé. All analog current and voltage bias values can be programmed through a digital interface. Additionally, integration time can be programmed with 0.1 µsec resolution by internal timing circuitry. ROIC has 1, 2 and 4 output modes with a frame rate of 120fps at 4 output mode. The design supports IntegrateThen-Read (ITR) and Integrate-While-Read (IWR) modes in snapshot operation. Photodetector reverse bias voltage is controlled by adjusting the bias of the common-gate input stage at the input of DI pixel. An on-chip low-dropout voltage regulator is used to generate the detector common voltage. With 2x2 binning feature, the ROIC can also be used for 30 µm pixel pitch 320x256 photodetector arrays. An Analog-Front-End (AFE) card has been designed to operate the ROIC and to convert analog video output to a 14-bit digital value. This digital video data is handled by external video processor card which supports 1-point and 2-point Non-Uniformity Correction (NUC), histogram equalization, bad pixel replacement and filtering. The ROIC has been extensively tested with a prototype FPA at 77°K. According to these test results, functionality of all modes have been verified and a noise level of 700é is achieved at 4.5Mé FWC.

We describe a technique for multiplexed imaging that is based on the concept of mapping scene features to unique temporal codes, and using smart digital pixels to efficiently decode at the focal-plane. We use this technique to demonstrate multiplexed multispectral imaging using actively encoded LEDs, and multiplexed hyperspectral imaging using a digital micromiror spatial light modulator. Both experiments utilize a computational imaging array comprised of a 32x32 array of digital pixels with the capability of acquiring eight concurrent measurements that can be modulated with a time-varying duo-binary signal (+1,-1,0) at MHz rates. This results in eight decoded images per frame at a maximum frame rate of 1600 frames per second. The total frame rate of the imaging system depends on the number of encoded features and the number of decoding channels within the digital pixel. We explore these trades as well as discuss limitations and areas for future improvement.

We report on product maturation of small pixel high definition high charge capacity 2.4 Mpixel MWIR Infrared Focal Plane Arrays. This high definition (HD) FPA utilizes a small 5 um pitch pixel size which enables near Nyquist limited sampling with by the optical system of many IR lenses. These smaller sub diffraction pitch pixels enable improved sensitivity and resolution resulting in clear, crisp high contrast imaging with excellent IFOVs even with small focal length lenses. The small pixel IR sensor allows the designer to trade off field of view, MTF, optics F/# to obtain a more compact and high performance IR sensor. This enables lower size, power and weight reductions of the entire IR Sensor System. The highly sensitive MWIR small pixel HD FPA has the capability to detect dimmer signals at longer ranges than previously demonstrated.

Leonardo MW (formerly Selex ES) has been developing infrared sensors and cameras for over 62 years at two main sites at Southampton and Basildon. Funding mainly from UK MOD has seen the technology progress from single element PbSe sensors to advanced, high definition, HgCdTe cameras, widely deployed in many fields today. However, in the last 10 years the major challenges and research funding has come from projects within the scientific sphere, particularly: astronomy and space. Low photon flux, high resolution spectroscopy and fast frame rates are the motivation to drive the sensitivity of infrared detectors to the single photon level. These detectors make use of almost noiseless avalanche gain in HgCdTe to achieve the sensitivity and speed of response. Metal Organic Vapour Phase Epitaxy, MOVPE, grown on low-cost GaAs substrates, provides the capability for crucial bandgap engineering to suppress breakdown currents and allow high avalanche gain even in very low background conditions. This paper describes the progress so far and provides a glimpse of the future.

My work in infrared technology dates back to 1980, and so almost 40 years have passed since I started in infrared focal plane array (IRFPA) R and D. Although our path was not in the mainstream, I have always enjoyed my research. In this paper, I introduce our accomplishments, including both PtSi Schottky-barrier (SB) and SOI diode uncooled IRFPAs, which were developed at Mitsubishi Electric. I have also been organizing the Infrared Array Sensor Forum (IRASF) at Ritsumeikan University since 2009. I also describe and explain the forum’s growth.

Quantum dot infrared photodetectors (QDIPs) have attracted significant attention due to selective photoresponse, high photoconductive gain, and numerous possibilities for nanoscale engineering of photoelectron processes, which control the detector characteristics. Our approach to improving QDIP performance is based on optimization of three dimensional nanoscale potential profile created by charged quantum dots (QDs). Nanoscale profile around QDs allows us to control photoelectron capture processes, which determines the photoelectron lifetime, detector operating speed, responsivity, the spectral density of noise, noise bandwidth, and the detector dynamic range. The nanoscale potential profile is determined by doping of QDs and inter-dot space. In this work, we study various ways of selective doping and its effects on characteristics of photodetectors. We investigate and compare intra-dot doping, inter-dot doping, and complex bipolar doping. To investigate effects of selective doping, we fabricated AlGaAs/InAs QD structures with n-doping of QD layers, structures with n-doping of barriers, and structures with p-doping of QD layers and n-doping of interdot space. We measured dark current, spectral photoresponse, voltage dependence of responsivity, and noise characteristic. The photoresponse is improved due to photon-electron coupling, which increases with QD filling by electrons. However, the noise current also increases due to increase in QD filling. Therefore, possibilities for improvement of QDIP structures with unipolar doping are very limited. Our results show that spectral photoresponse, responsivity, and detector sensitivity are substantially improved due to bipolar doping, which provides decoupled control of electron filling of QDs and the potential barriers around QDs.

We designed R-QWIP devices for narrowband 10.6 μm detection. Despite the low doping of 0.2 and 0.3 × 10¹⁸ cm^-3 and thin absorbing layer thickness of 1 μm, the observed QE is 29% and 26%, respectively. This level of QEs, combined with the large photoconductive gain in a thin layer, produces large conversion efficiencies of 20% and 15% for large photocurrents. The high photocurrent and low dark current brought by low doping thus allow the QWIPs to be BLIP at 65 K with an 11 μm cutoff. The projected NETD is 20 mK at 60 K, demonstrating the high performance of R-QWIPs.

Quantum well infrared photodetectors (QWIPs) based on GaAs have attracted much attention owing to its matured material growth technique. In order to obey the selection rule of polarization, various grating structures have been attached to planar QWIPs. Recently, we experimentally demonstrated that strained planar QWIPs could be self-rolled up into an out-of-plane tubular geometry so that the polarization selection rule is sufficiently subdued without any extra grating structure. Such self-rolled-up QWIPs show a broadband enhancement of responsivity and detectivity over a wide incident angle. In this paper, both wave-optics and ray-optics simulations are performed to clarify the underlying physics. The well-defined curved QWIPs pave a path towards flexible QWIPs for flexible optoelectronics.

Continuing with its legacy of producing high performance infrared detectors, IRnova introduces its high resolution LWIR IDDCA (Integrated Detector Dewar Cooler assembly) based on QWIP (quantum well infrared photodetector) technology. The Focal Plane Array (FPA) has 640×512 pixels, with small (15μm) pixel pitch, and is based on the FLIRIndigo ISC0403 Readout Integrated Circuit (ROIC). The QWIP epitaxial structures are grown by metal-organic vapor phase epitaxy (MOVPE) at IRnova. Detector stability and response uniformity inherent to III/V based material will be demonstrated in terms of high performing detectors. Results showing low NETD at high frame rate will be presented. This makes it one of the first 15μm pitch QWIP based LWIR IDDCA commercially available on the market. High operability and stability of our other QWIP based products will also be shared.

The hole diffusion length in n-InGaAs is extracted for two samples of different doping concentrations using a set of long and thin diffused junction diodes separated by various distances on the order of the diffusion length. The methodology is described, including the ensuing analysis which yields diffusion lengths between 70 - 85 μm at room temperature for doping concentrations in the range of 5 − 9 × 10¹⁵ cm⁻³ . The analysis also provides insight into the minority carrier mobility which is a parameter not commonly reported in the literature. Hole mobilities on the order of 500 − 750 cm²/V·s are reported for the aforementioned doping range, which are comparable albeit longer than the majority hole mobility for the same doping magnitude in p-InGaAs. A radiative recombination coefficient of (0.5±0.2)×10⁻¹⁰ cm⁻³ s −1 is also extracted from the ensuing analysis for an InGaAs thickness of 2.7 μm. Preliminary evidence is also given for both heavy and light hole diffusion. The dark current of InP/InGaAs p-i-n photodetectors with 25 and 15 μm pitches are then calibrated to device simulations and correlated to the extracted diffusion lengths and doping concentrations. An effective Shockley-Read-Hall lifetime of between 90-200 μs provides the best fit to the dark current of these structures.

Graphene is an atomically thin carbon layer with a two-dimensional hexagonal lattice structure and has rich optoelectronic properties well suited to a wide range of applications. Graphene is considered to be a promising material for photodetectors because it exhibits excellent properties such as broadband absorption covering at least the ultraviolet to terahertz frequencies. However, the low optical absorption of graphene, at ca. 2.3%, still remains an important problem. Plasmonic metamaterial structures are good candidates to address this challenge. Metal-insulator-metal-based plasmonic metamaterial absorbers (MIM-PMAs) are highly suitable for the introduction and application of graphene. MIM-PMAs have a multilayer structure that includes plasmonic micropatches, an insulator, and a metal reflector layer. MIM-PMAs exhibit wavelength-selective absorption according to the micropatch size. Our previous research has demonstrated that the optical absorption of graphene is enhanced only by the main plasmonic resonance mode, and the plasmonic resonance modes in MIM-MPAs are strongly influenced by the insulator material. Therefore, the insulator layer plays an important role in graphene-coated MIM-PMAs. In this study, we have investigated the effect of the insulator layer in graphene-covered MIM-PMAs. The graphene was fabricated by chemical vapor deposition and transferred onto MIM-PMAs with different insulator thicknesses. Reflectance measurements demonstrated that varying the insulator thickness had a significant effect on the absorbance of graphene and resulted in modulation of the absorption wavelength. These results indicate that the plasmonic resonance localized at graphene near the plasmonic micropatches is modulated by the waveguide mode in the insulator layer. We believe that the present study will lead to significant improvements in graphene-based infrared detectors.