This PDF file contains the front matter associated with SPIE Proceedings Volume 9070, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

In this paper we present first results from a backside illuminated CMOS image sensor that we fabricated on high resistivity silicon. Compared to conventional CMOS imagers, a thicker photosensitive membrane can be depleted when using silicon with low background doping concentration while maintaining low dark current and good MTF performance. The benefits of such a fully depleted silicon sensor are high quantum efficiency over a wide spectral range and a fast photo detector response. Combining these characteristics with the circuit complexity and manufacturing maturity available from a modern, mixed signal CMOS technology leads to a new type of sensor, with an unprecedented performance spectrum in a monolithic device. Our fully depleted, backside illuminated CMOS sensor was designed to operate at integration times down to 100nsec and frame rates up to 1000Hz. Noise in Integrate While Read (IWR) snapshot shutter operation for these conditions was simulated to be below 10e^- at room temperature. 2×2 binning with a 4× increase in sensitivity and a maximum frame rate of 4000 Hz is supported. For application in hyperspectral imaging systems the full well capacity in each row can individually be programmed between 10ke^-, 60ke^- and 500ke^-. On test structures we measured a room temperature dark current of 360pA/cm² at a reverse bias of 3.3V. A peak quantum efficiency of 80% was measured with a single layer AR coating on the backside. Test images captured with the 50μm thick VGA imager between 30Hz and 90Hz frame rate show a strong response at NIR wavelengths.

Low light level imaging applications requiring high detectivity demand photon shot noise limited performance at temperatures near 300K. Analytical models, however, have provided limited insight on underlying mechanisms limiting performance in conventional planar double heterointerface In_0.53Ga_0.47As on InP P⁺n photodiodes for imaging the visible and short wave infrared. Quantitative modeling provides tools to investigate performance sensitivities and their underlying mechanisms. In this work we use three-dimensional numerical simulation to investigate intrinsically limited diffusion and Shockley-Read-Hall generation recombination dark currents for a planar P⁺n photodiode situated in a 3×3 mini array. We assess the influence of geometry by varying pitch, junction location, and photodiode size. Modeling shows that SRH generation currents, not including surface effects, vary with both junction perimeter and area, and that the perimeter component dominates small radius junctions. By varying the axial junction placement we show that widegap junctions result in bias-dependent quantum efficiencies that require higher reverse bias, and result in higher dark currents, than shallow homojunctions at comparable efficiencies. Finally, numerical simulation explains lateral diffusion current suppression in dense arrays in terms of suppressed minority carrier density gradients. The analysis demonstrates that the boundary condition applicable to dense arrays requires no lateral diffusion current at symmetry planes bisecting segments connecting uniformly reverse biased nearest neighbor diodes. Following Grimbergen, this leads to radial geometry curves describing dark intrinsic diffusion reductions with pitch. The quantitative modeling provides insight explaining the observation that the ideal diode equation correctly estimates dense array dark diffusion currents.

Processing improvements have facilitated manufacturing reduced pixel dimensions for lattice-matched InGaAs on InP short-wave infrared detectors. Due to its technological maturity, this material system continues to garner attention for low-light level imaging applications. With pixel dimensions smaller than minority carrier diffusion lengths, optimizing array performance by reducing crosstalk from lateral carrier diffusion remains an important design issue. Analytical models, however, have provided limited insight on underlying mechanisms limiting device performance in the conventional planar double heterointerface device. Quantitative modeling provides tools to investigate performance sensitivities and their underlying mechanisms. In this work we develop a three-dimensional numerical simulation for dense P⁺n In_0.53Ga_0.47As on InP photo detector focal plane arrays using a conventional planar, back-illuminated structure. We evaluate optical generation with finite-difference time-domain analysis, and model carrier transport in a drift diffusion analysis simultaneously solving the carrier continuity and Poisson equations. Using this model we investigate modulation transfer function variations with pixel pitch and diffused junction geometries for small dimension arrays. By accounting for carrier diffusion effects, these results should provide a benchmark against which to evaluate modulation transfer function contributions from other effects, such as crosstalk attributable to photon recycling.

SWIR detection band benefits from natural (sun, night glow, thermal radiation) or artificial (eye safe lasers) photons sources combined to low atmospheric absorption and specific contrast compared to visible wavelengths. It gives the opportunity to address a large spectrum of applications such as defense and security (night vision, active imaging), space (earth observation), transport (automotive safety) or industry (non destructive process control). InGaAs material appears as a good candidate to satisfy SWIR detection needs. The lattice matching with InP constitutes a double advantage to this material: attractive production capacity and uncooled operation thanks to low dark current level induced by high quality material. The recent transfer of imagery activities from III-VLab to Sofradir provides a framework for the production activity with the manufacturing of high performances products: CACTUS320 SW and CACTUS640 SW. The developments, begun at III-Vlab towards VGA format with 15μm pixel pitch, lead today to the industrialization of a new product: SNAKE SW. On one side, the InGaAs detection array presents high performances in terms of dark current and quantum efficiency. On the other side, the low noise ROIC has different additional functionalities. Then this 640×512 @ 15μm module appears as well suited to answer the needs of a wide range of applications. In this paper, we will present the Sofradir InGaAs technology, some performances optimization and the last developments leading to SNAKE SW.

High Sensitivity Megapixel and VGA shortwave IR imagers are presented. The imagers have 1280×1024 and 640×512 resolution FPAs with 12.5 μm pitch. The associated camera electronics are designed to optimize small SWaP and performance for a variety of applications including man-portable and airborne systems. Performance characterization of both these imagers is presented showing low-noise, high dynamic range capability suitable for challenging operational environments including light-starved and urban environments as well as a variety of industrial applications.

Photon counting imaging applications requires low noise from both detector and readout integrated circuit (ROIC) arrays. In order to retain the photon-counting-level sensitivity, a long integration time has to be employed and the dark current has to be minimized. It is well known that the PIN dark current is sensitive to temperature and a dark current density of 0.5 nA/cm² was demonstrated at 7 °C previously. In order to restrain the size, weight, and power consumption (SWaP) of cameras for persistent large-area surveillance on small platforms, it is critical to develop large format PIN arrays with small pitch and low dark current density at higher operation temperatures. Recently Spectrolab has grown, fabricated and tested 1024x1280 InGaAs PIN arrays with 12.5 μm pitch and achieved 0.7 nA/cm² dark current density at 15 °C. Based on our previous low-dark-current PIN designs, the improvements were focused on 1) the epitaxial material design and growth control; and 2) PIN device structure to minimize the perimeter leakage current and junction diffusion current. We will present characterization data and analyses that illustrate the contribution of various dark current mechanisms.

Detectors for the short-wave infrared (SWIR) spectral range are particularly suitable for observation under hazy weather conditions as well as under twilight or moon light conditions. In addition, SWIR detectors allow using the airglow for observation under moonless sky. SWIR detectors are commonly based on InGaAs or HgCdTe (MCT) and demand extremely low dark currents to ensure a high signal-to-noise ratio under low background light conditions. AIM has developed a read-out integrated circuit (ROIC) with 640×512 pixels and a 15 μm pixel pitch for low light level applications. The ROIC supports analog or digital correlated double sampling (CDS) for the reduction of reset-noise (also known as kTC-noise). Along with CDS, a rolling shutter (RS) mode has been implemented. The input stage of the ROIC is based on a capacitive transimpedance amplifier (CTIA) with two selectable gain settings. The dark current of our SWIR MCT detectors has recently been significantly reduced to allow for high operating temperatures. In contrast to InGaAs, the MCT material offers the unique possibility to adjust the cut-off wavelength according to the application while maintaining the matching of the lattice constant to the one of the CdZnTe substrate. The key electro-optical performance parameters of lately developed MCT based SWIR Focal Plane Arrays (FPA) with a 1.75 μm cut-off wavelength will be presented. In addition, AIMs SWIR detectors covering the spectral range from 0.9 μm to 2.5 μm and available in formats of 384×288 pixels - 24 μm pitch and 1024×256 pixels - 24×32 μm², will be introduced.

We report the development of high performance low cost SWIR infrared detectors from MBEgrown HgCdTe on 3-inch CdTe-buffered silicon substrates. The experimental findings demonstrate that despite the large lattice mismatch between HgCdTe and Si substrate, the materials and detector performances are sufficiently better than those reported for III-V mixed crystals. High minority carrier lifetime of the order 3 μs at room temperature was measured on the as grown material. Photodetectors fabricated from this material produced low dark current densities on the order of 10^-6 A/cm² and 10^-3 A/cm² at 200K and 300K. Quantum efficiency exceeding 70% at 2.0 μm, without antireflective coating, was measured on single element detectors. Further, 320 X 256, 30 μm pitch FPA’s have been fabricated with this HgCdTe on Si material and dark current operability of ~ 99.5% (mean dark current of 30 pA/Pixel) at 200K has been demonstrated.

This paper reports the development of a new miniature VGA SWIR camera called NanoCAM-6415, which is developed to demonstrate the key features of the MT6415CA ROIC such as high integration level, low-noise, and low-power in a small volume. The NanoCAM-6415 uses an InGaAs Focal Plane Array (FPA) with a format of 640 × 512 and pixel pitch of 15 μm built using MT6415CA ROIC. MT6415CA is a low-noise CTIA ROIC, which has a system-on-chip architecture, allows generation of all the required timing and biases on-chip in the ROIC without requiring any external components or inputs, thus enabling the development of compact and low-noise SWIR cameras, with reduced size, weight, and power (SWaP). NanoCAM-6415 camera supports snapshot operation using Integrate-Then-Read (ITR) and Integrate-While-Read (IWR) modes. The camera has three gain settings enabled by the ROIC through programmable Full-Well-Capacity (FWC) values of 10.000 e-, 20.000 e-, and 350.000 e- in the very high gain (VHG), high-gain (HG), and low-gain (LG) modes, respectively. The camera has an input referred noise level of 10 e- rms in the VHG mode at 1 ms integration time, suitable for low-noise SWIR imaging applications. In order to reduce the size and power of the camera, only 2 outputs out of 8 of the ROIC are connected to the external Analog-to-Digital Converters (ADCs) in the camera electronics, providing a maximum frame rate of 50 fps through a 26-pin SDR type Camera Link connector. NanoCAM-6415 SWIR camera without the optics measures 32 mm × 32 mm × 35 mm, weighs 45gr, and dissipates less than 1.8 W using a 5 V supply. These results show that MT6415CA ROIC can successfully be used to develop cameras for SWIR imaging applications where SWaP is a concern. Mikro-Tasarim has also developed new imaging software to demonstrate the functionality of this miniature VGA camera. Mikro-Tasarim provides tested ROIC wafers and also offers compact and easy-to-use test electronics, demo cameras, and hardware/software development kits for its ROIC customers to shorten their FPA and camera development cycles.

A SWIR FPA was designed and manufactured with 640*512 pixels, 20 μm pitch and InGaAs detectors for electroluminescence characterization and astronomical applications in the [0.9 – 1.55 μm] range. The FPA is mounted in a liquid nitrogen dewar and is operated by a low noise frontend electronics. One of the biggest problem in designing sensors and cameras for electro-luminescence measurements is the autoillumination of the detectors by the readout circuit. Besides of proper shielding of the detectors, the ROIC shall be optimized for minimal electrical activity during the integration time of the very-weak signals coming from the circuit under test. For this reason a SFD (or Source Follower per Detector) architecture (like in the Hawaii sensor) was selected, resulting in a background limited performance of the detector. The pixel has a (somewhat arbitrary) full well capacity of 400 000 e^- and a sensitivity of 2.17 μV/e^-. The dark signal is app. 1 e-/pixel/sec and with the appropriate Fowler sampling the dark noise lowers below 5 e^-_rms. The power consumption of the circuit is limited 2 mW, allowing more than 24 hours of operation on less than 1 l of liquid nitrogen. The FPA is equipped with 4 outputs (optional readout on one single channel) and is capable of achieving 3 frames per second. Due to the non-destructive readout it is possible to determine in a dynamic way the optimal integration time for each observation. The Cougar camera is equipped with ultra-low noise power supply and bias lines; the electronics contain also a 24 bit AD converter to fully exploit the sensitivity of the FPA and the camera.

Extended wavelength InGaAs infrared detector arrays in 1.0~2.5μm spectral rang based on three types of material structures grown by MBE were studied. The first type InGaAs detectors, marked by sample 1#, were fabricated using Pi- N epitaxial materials, mesa etching technique, side-wall and surface passivating film. The second type InGaAs detectors, marked by sample 2#, were fabricated using N-i-P epitaxial materials, mesa etching technique, side-wall and surface passivating film. The third type InGaAs detectors, marked by sample 3#, were fabricated using n-i-n epitaxial materials, planar diffusion process and surface passivating coating. I-V curves, low frequency noise and response spectra of these detectors were measured at the different temperature. The response spectra of these detectors cover 1.0~2.5μm wavelength range. The dark current density of three types InGaAs detectors are 28nA/cm², 2μA/cm², 9μA/cm² at 200K and -10mV bias voltage, respectively. Compared to Sample 2# and Sample 3#, sample 1# presents the lower dark current at the same temperature and the same bias voltage, which mainly results in the improvement of surface passivation film and the depth of mesa etching. The frequency spectrum of the noise of sample 1# has an inflection point at about 10Hz frequency, 1/f noise play an obviously role in the detectors below the 10Hz frequency.

This paper presents novel unit cell architecture for short wave infrared (SWIR) imaging applications. It has two input stages which are CTIA and SFD covering for both respectively low and high light, levels and automatic input stage selection circuitry that chooses best input stage. User can select 2 modes for FPA manual and automatic mode. In manual mode, user can set CTIA or SFD for all pixels according to user needs. In automatic mode, each pixel selects input stage itself according to light level. Light level threshold can be adjusted with reference voltage. Automatic input stage selection for each pixel brings high SNR level and low noise along with highest possible dynamic range for SWIR imaging applications. CMOS 0.18μm technology is used to realize unit cell. In the architecture of unit cell, circuit level techniques are used to optimize layout size.

Over the past decade, we have witnessed a growing demand for electro-optical systems that can provide continuous 360⁰ coverage. Applications such as perimeter security, autonomous vehicles, and military warning systems are a few of the most common applications for panoramic imaging. There are several different technological approaches for achieving panoramic imaging. Solutions based on rotating elements do not provide continuous coverage as there is a time lag between updates. Continuous panoramic solutions either use "stitched" images from multiple adjacent sensors, or sophisticated optical designs which warp a panoramic view onto a single sensor. When dealing with panoramic imaging in the visible spectrum, high volume production and advancement of semiconductor technology has enabled the use of CMOS/CCD image sensors with a huge number of pixels, small pixel dimensions, and low cost devices. However, in the infrared spectrum, the growth of detector pixel counts, pixel size reduction, and cost reduction is taking place at a slower rate due to the complexity of the technology and limitations caused by the laws of physics. In this work, we will explore the challenges involved in achieving 360⁰ panoramic thermal imaging, and will analyze aspects such as spatial resolution, FOV, data complexity, FPA utilization, system complexity, coverage and cost of the different solutions. We will provide illustrations, calculations, and tradeoffs between three solutions evaluated by Opgal: A unique 360⁰ lens design using an LWIR XGA detector, stitching of three adjacent LWIR sensors equipped with a low distortion 1200 lens, and a fisheye lens with a HFOV of 180º and an XGA sensor.

In the continuity of its current strategy, HGH maintains a deep effort in developing its most recent product family: the infrared (IR) panoramic 360-degree surveillance sensors. During the last two years, HGH optimized its prototype Middle Wave IR (MWIR) panoramic sensor IR Revolution 360 HD that gave birth to Spynel-S product. Various test campaigns proved its excellent image quality. Cyclope, the software associated with Spynel, benefitted from recent image processing improvements and new functionalities such as target geolocalization, long range sensor slue to cue and facilitated forensics analysis. In the frame of the PANORAMIR project sustained by the DGA (Délégation Générale de l’Armement), HGH designed a new extra large resolution sensor including a MWIR megapixel Focal Plane Array (FPA) detector (1280×1024 pixels). This new sensor is called Spynel-X. It provides outstanding resolution 360-degree images (with more than 100 Mpixels). The mechanical frame of Spynel (-S and -X) was designed with the collaboration of an industrial design agency. Spynel got the “Observeur du Design 2013” label.

The development of a new thermal imaging camera, for long range surveillance applications, is described together with the enabling technology. Previous publications have described the development of large arrays of 12μm pixels using Metal Organic Vapour Phase Epitaxy (MOVPE) grown Mercury Cadmium Telluride (MCT) for wide area surveillance applications. This technology has been leveraged to produce the low cost 1280×720 pixel Medium Wave IR focal plane array at the core of the new camera. Also described is the newly developed, high performance, ×12 continuous zoom lens which, together with the detector, achieves an Instantaneous Field of View (IFOV) of 12.5μrad/pixel enabling long detection, recognition and identification ranges. Novel image processing features, including the turbulence mitigation algorithms deployed in the camera processing electronics, are also addressed. Resultant imagery and performance will be presented.

The tomographic scanner (TOSCA) detects signals using line detectors scanning a scene at regularly distributed angles. These line scan signals are then processed to reconstruct 2-dimensional images. In the simplest form, a 1-axis rotating conical scan optics scans across a simple patterned reticle, the signal collection being done with a single pixel detector. Experimental mono- and multispectral cameras using this approach are demonstrated under varying illumination conditions. Of particular interest is the TOSCA system’s ability to handle and compensate for light sources modulated with a frequency higher than that of the frame rate. We also demonstrate for the first time a TOSCA imager operating in the infrared region. The device is put together using 3D-printed key parts and low cost optical components, leading to a very economical infrared camera.

Operating in a degraded visual environment due to darkness can pose a threat to navigation safety. Systems have been developed to navigate in darkness that depend upon differences between objects such as temperature or reflectivity at various wavelengths. However, adding sensors for these systems increases the complexity by adding multiple components that may create problems with alignment and calibration. An approach is needed that is passive and simple for widespread acceptance. Our approach uses a type of augmented display to show fused images from visible and thermal sensors that are continuously updated. Because the raw fused image gave an unnatural color appearance, we used a color transfer process based on a look-up table to replace the false colors with a colormap derived from a daytime reference image obtained from a public database using the GPS coordinates of the vehicle. Although the database image was not perfectly registered, we were able to produce imagery acquired at night that appeared with daylight colors. Such an approach could improve the safety of nighttime navigation.

For years, scientists have been using broadband cameras to perform measurements in the infrared spectral bands. In order to improve the outcomes of these studies, Telops has developed a fast multispectral imaging system in the LWIR and MWIR band. This paper presents the improvement that a fast infrared multispectral imager adds to the traditional infrared investigations and how this system can be applied in defence innovation research. An overview over the technology is presented and discussed along the results obtained during a combustion experiment.

The conventional photographs only record the sum total of light rays of each point on image plane so that they tell little about the amount of light traveling along individual rays. The focus and lens aberration problems have challenged photographers since the very beginning therefore light field photography was proposed to solve these problems. Lens array and multiple camera systems are used to capture 4D light rays, by reordering the different views of scene from multiple directions. The coded aperture is another method to encode the angular information in frequency domain. However, infrared light field sensing is still widely opening to research. In the paper, we will propose micro plane mirror optics together with compressive sensing algorithm to record light field in infrared spectrum. The micro mirror reflects objects irradiation and forms a virtual image behind the plane in which the mirror lies. The Digital Micromirror (DMD) consists of millions microscale mirrors which work as CCD array in the camera and it is controlled separately so as to project linear combination of object image onto lens. Coded aperture could be utilized to control angular resolution of infrared light rays. The carbon nanotube based infrared detector, which has ultra high signal to noise ratio and ultra fast responsibility, will sum up all image information on it without image distortion. Based on a number of measurements, compressive sensing algorithm was used to recover images from distinct angles, which could compute different views of scene to reconstruct infrared light field scence. Two innovative applications of full image recovery using nano scale photodetector and DMD based synthetic aperture photography will also be discussed in this paper.

HySpex ODIN-1024 is a next generation state-of the-art airborne hyperspectral imaging system developed by Norsk Elektro Optikk AS. Near perfect coregistration between VNIR and SWIR is achieved by employing a novel common fore-optics design and a thermally stabilized housing. Its unique design and the use of state-of-the-art MCT and sCMOS sensors provide the combination of high sensitivity and low noise, low spatial and spectral misregistration (smile and keystone) and a very high resolution (1024 pixels in the merged data products). In addition to its supreme data quality, HySpex ODIN-1024 includes real-time data processing functionalities such as real-time georeferencing of acquired images. It also features a built-in onboard calibration system to monitor the stability of the instrument. The paper presents data and results from laboratory tests and characterizations, as well as results from airborne measurements.

Today's world is going mobile. Smartphone devices have become an important part of everyday life for billions of people around the globe. Thermal imaging cameras have been around for half a century and are now making their way into our daily lives. Originally built for military applications, thermal cameras are starting to be considered for personal use, enabling enhanced vision and temperature mapping for different groups of professional individuals. Through a revolutionary concept that turns smartphones into fully functional thermal cameras, we have explored how these two worlds can converge by utilizing the best of each technology. We will present the thought process, design considerations and outcome of our development process, resulting in a low-power, high resolution, lightweight USB thermal imaging device that turns Android smartphones into thermal cameras. We will discuss the technological challenges that we faced during the development of the product, and what are the system design decisions taken during the implementation. We will provide some insights we came across during this development process. Finally, we will discuss the opportunities that this innovative technology brings to the market.

Infrared technology and imaging systems are already used extensively by the law enforcement (LE) community, typically to gain a tactical advantage or obtain immediate situational awareness. As the use of infrared technology becomes more affordable and widespread, LE is finding new ways to use it and leverage the results in the courtroom as evidence. A case study will be presented where infrared imagery was used to support the Portland Police Bureau (PPB) in prosecuting an individual for a crime where a conviction might not have been assured without said imagery. Tests conducted at FLIR Systems, combined with expert witness testimony by a FLIR employee, helped a jury understand the significance of a key piece of infrared evidence, resulting in a conviction of the criminal. This case was the first Federal case of its kind where infrared imagery was used forensically as evidence and, as such, established precedence. Prior to this, infrared imagery has been offered and debated in court only as to whether it constitutes a legal search. Courtroom observations and lessons learned from this trial have shown that both industry and LE can do a better job of making the prosecution’s cases stronger utilizing infrared technology and thus taking criminals off the street.

This paper shows the current status of cooled IR detector technologies at i3system, South Korea. Mass production technology of i3system has successfully supplied lots of QVGA cooled IR detectors to camera customers. i3system has also developed small pitch cooled IR detectors with 320×256 and 640×512 formats for several different applications such as thermal sights and 24-hour operation observation units. In 2013, i3system’s cooled IR detector has been launched in STSAT(Science and Technology SATellite)-2C through Naro-1 program which was South Korea’s first successful launch vehicle for satellite. Owing to i3system’s robust, intensive design and test programs, IR detector technologies have been space qualified without any further efforts by the space program. Currently, development programs for SXGA(1280×1024) with small pitch cooled detector are being progressed and its status is addressed.

Electro-optical missile seekers pose exceptional requirements for infrared (IR) detectors. These requirements include: very short mission readiness (time-to-image), one-time and relatively short mission duration, extreme ambient conditions, high sensitivity, fast frame rate, and in some cases small size and cost. SCD is engaged in the development and production of IR detectors for missile seeker applications for many years. 0D, 1D and 2D InSb focal plane arrays (FPAs) are packaged in specially designed fast cool-down Dewars and integrated with Joule-Thomson (JT) coolers. These cooled MWIR detectors were integrated in numerous seekers of various missile types, for short and long range applications, and are combat proven. New technologies for the MWIR, such as epi-InSb and XBn-InAsSb, enable faster cool-down time and higher sensitivity for the next generation seekers. The uncooled micro-bolometer technology for IR detectors has advanced significantly over the last decade, and high resolution - high sensitivity FPAs are now available for different applications. Their much smaller size and cost with regard to the cooled detectors makes these uncooled LWIR detectors natural candidates for short and mid-range missile seekers. In this work we will present SCD's cooled and uncooled solutions for advanced electro-optical missile seekers.

Today, both military and civilian applications require miniaturized optical systems in order to give an imagery function to vehicles with small payload capacity. After the development of megapixel focal plane arrays (FPA) with micro-sized pixels, this miniaturization will become feasible with the integration of optical functions in the detector area. In the field of cooled infrared imaging systems, the detector area is the Detector-Dewar-Cooler Assembly (DDCA). SOFRADIR and ONERA have launched a new research and innovation partnership, called OSMOSIS, to develop disruptive technologies for DDCA to improve the performance and compactness of optronic systems. With this collaboration, we will break down the technological barriers of DDCA, a sealed and cooled environment dedicated to the infrared detectors, to explore Dewar-level integration of optics. This technological breakthrough will bring more compact multipurpose thermal imaging products, as well as new thermal capabilities such as 3D imagery or multispectral imagery. Previous developments will be recalled (SOIE and FISBI cameras) and new developments will be presented. In particular, we will focus on a dual-band MWIR-LWIR camera and a multichannel camera.

New development of imaging systems implies the use of multi band wavelength, VIS and IR, for imaging enhancement and more data presenting. Some of those systems, such as <see spot<, are designed for applications requiring in plus, the ability to see the aiming point of a laser designator. The use of a designating laser to assist in target identification and tracking can unintentionally result in a laser beam reflected back into the sensor, leading to transient dazzling or permanent damage of the sensor. We propose a novel passive Wideband Protection Filter (WPF) that blocks the transmission only if the power exceeds a certain threshold. We present a special design of WPF suitable for dual- and multi- band wavelength range, including transmission and functionality performances. We demonstrate a new design transferring our WPF filter from VIS/NIR into the MW/LWIR.

To enable higher operating temperatures in InAs/GaSb superlattice detectors for the long-wavelength infrared atmospheric window at 8-12 μm, a reduction of the bulk dark current density is indispensable. To reduce the dark current of conventional homojunction pin-diode device designs, bandstructure-engineering of the active region is considered most promising. So far, several successful device concepts have been demonstrated, yet they all rely on the inclusion of Aluminum within the active layers. Driven by manufacturing aspects we propose an Al-free heterojunction device concept that is based on a p⁺-doped InAs/GaSb superlattice absorber layer combined with an adjacent N^--doped high gap region, which again is realized with an InAs/GaSb superlattice. To calculate the superlattice band gap and the position of the conduction band edge at the heterojunction we employ the Superlattice Empirical Pseudopotential Method. With a series of three heterojunction p⁺N^- InAs/GaSb superlattice devices with an absorber band gap of 124 meV (10.0 μm) we give a first proof of the advocated device concept.

InAs/GaSb Type II superlattices (T2SLs) are a promising III-V alternative to HgCdTe (MCT) for infrared Focal Plane Array (FPA) detectors. Over the past few years SCD has developed the modeling, growth, processing and characterization of high performance InAs/GaSb T2SL detector structures suitable for FPA fabrication. Our LWIR structures are based on an XB_pp design, analogous to the XB_nn design that lead to the recent launch of SCD’s InAsSb HOT MWIR detector (T_OP= 150 K). The T2SL XB_pp structures have a cut-off wavelength between 9.0 and 10.0 μm and are diffusion limited with a dark current at 78K that is within one order of magnitude of the MCT Rule 07 value. We demonstrate 30 μm pitch 5 × 5 test arrays with 100% operability and with a dark current activation energy that closely matches the bandgap energy measured by photoluminescence at 10 K. From the dependence of the dark current and photocurrent on mesa size we are able to determine the lateral diffusion length and quantum efficiency (QE). The QE agrees very well with the value predicted by our recently developed k · p model [Livneh et al, Phys. Rev. B86, 235311 (2012)]. The model includes a number of innovations that provide a faithful match between measured and predicted InAs/GaSb T2SL bandgaps from MWIR to LWIR, and which also allow us to treat other potential candidate systems such as the gallium free InAs/InAsSb T2SL. We will present a critical comparison of InAs/InAsSb vs. InAs/GaSb T2SLs for LWIR FPA applications.

InAs/GaSb superlattices are characterized by a broken-gap type II band alignment. Their effective band gap can be engineered to match mid to long wavelength infrared (IR) photon energies. Fraunhofer IAF has developed image detectors for threat warning systems based on this material system that are capable of spatially and temporally coincident detection in two mid-IR wavelength ranges. We review the present status of the processing technology, report continuous improvements achieved in key areas of detector performance, including defect density and noise behavior, and present initial results for statistical characterization of ensembles of detector elements with respect to diode characteristics and noise.

We first present an electro-optical characterization of the radiometric performances of a type-II InAs/GaSb superlattice (T2SL) pin photodiode operating in the mid-wavelength infrared domain. This photodiode was grown with an InAs-rich structure. We focused our attention on quantum efficiency and responsivity: quantum efficiency of mono-pixel device reaches 23% at λ = 2.1 μm for 1 μm thick SL structure and 77K operating temperature. Then we measured the angular response of this photodiode: the response of the photodiode doesn’t depend on the angle of incidence of the flux. We also report the QE of 2μm-thick InAs-rich T2SL pin 320×256 pixels focal plane array, which reaches 61% at λ = 2.6 μm.

Detectivity of mid-wave infrared (MWIR) detectors based on InAs/GaSb type II strained layer superlattices (T2SLs) can be significantly enhanced at select wavelengths by integrating the detector with a back-side illuminated plasmonic coupler. The application of a simple metal-T2SL structure directly on the GaSb substrate can result in radiation losses into the substrate due to the low refractive index of T2SL layer. However, insertion of a higher refractive index material, such as germanium (Ge), into the metal-SLS structure can confine the surface plasmon waveguide (SPW) modes to the surface. In this work, metal (Au)-Ge-T2SL structures are designed with an approximately 100 nm thick Ge layer. The T2SL layer utilized a p-i-n detector design with 8 monolayers (MLs) InAs/8 MLs GaSb. A plasmonic coupler was then realized inside the 300 μm circular apertures of these single element detectors by the formation of a corrugated metal (Au) surface. The T2SL single element detector integrated with an optimized plasmonic coupler design increased the quantum efficiency (QE) by a factor of three at an operating temperature of 77 K and 3 to 5 μm illumination wavelength, compared to a reference detector structure, and each structure exhibited the same level of dark current.

Focal plane array based on InAs/GaSb type-II superlattice (T2SL) is expected as an alternative to HgCdTe. To get more competitive performance of T2SL detector, we need building up more reliable fabrication process. Especially, mesa formation and passivation with understanding of surface leakage mechanism is critical issue. Generally, the existence of dangling bonds at crystal surface or damaged layer and native oxides on etched mesa sidewall leads to surface leakage currents, which mostly degrade the detector performance. Many researchers adopted SiO2 film as an effective passivation layer, which was deposited by plasma enhanced chemical vapor deposition at low temperature. However, good passivation requires not only stable film, but also an effective surface treatment before passivation. There are few reports, which discuss the relation between treatment before passivation and device characteristics in T2SL photodetectors. In this work, we present dry etching mesa formation and the effect of pretreatment of passivation on T2SL p-i-n photodetector fabrication. We investigate R0A-Perimeter/Area relation and R0A temperature dependence with in-situ plasma treatment prior to the passivation. From results of electrical characterization and interface analysis using STEM, it is recognized that in-situ N2 plasma treatment was effective to surface leakage reduction.

In past decade, T2SL detectors with promising performance have been reported by various institutions thanks to the extensive modeling efforts, improvement of T2SL material quality, and development of advanced low-dark-current architectures with unipolar barriers (Xbn, CBIRD, pBiBn, M-structure, etc). One of the most demanding challenges of present day T2SL technology is the suppression of surface leakage currents associated with the exposed mesa sidewalls, which appear during the definition of device optical area. Typical FPA pixels have large surface/volume ratio and their performance is strongly dependent on surface effects. In order to overcome the limitation imposed by surface leakage currents, a stable surface passivation layer is needed. In this paper we report on InAs/GaSb T2SL detectors operating in the LWIR spectral region (100% cut-off wavelength of ~10 μm at 77K) passivated with epitaxially grown ZnTe. In order to compensate for the high conductivity of ZnTe passivation it was doped with chlorine to 1 × 10¹⁸cm⁻³ concentration. Dark current measurements reveal the significant reduction of noise current after ZnTe passivation.

The effect of defects on the dark current characteristics of MWIR, III-V nBn detectors has been studied. Two different types of defects are compared, those produced by lattice mismatch and by proton irradiation. It is shown that the introduction of defects always elevates dark currents; however the effect on dark current is different for nBn detectors and conventional photodiodes. The dark currents of nBn detectors are found to be more tolerant of defects compared to pn-junction based devices. Defects more weakly increase dark currents, and cooling reduces the defect-produced dark currents more rapidly in nBn detectors than in conventional photodiodes.

Commercially available read out integrated circuits (ROICs) require the FPA to have high dynamic resistance area product at zero bias (R0A) which is directly related to dark current of the detector. Dark current arises from bulk and surface contributions. Recent band structure engineering studies significantly suppressed the bulk contribution of the type-II superlattice infrared photodetectors (N structure, M structure, W structure). In this letter, we will present improved dark current results for unipolar barrier complex supercell superlattice system which is called as “N structure”. The unique electronic band structure of the N structure increases electron-hole overlap under bias, significantly. N structure aims to improve absorption by manipulating electron and hole wavefunctions that are spatially separated in T2SLs, increasing the absorption while decreasing the dark current. In order to engineer the wavefunctions, we introduce a thin AlSb layer between InAs and GaSb layers in the growth direction which also acts as a unipolar electron barrier. Despite the difficulty of perfect lattice matching of InAs and AlSb, such a design is expected to reduce dark current. Experiments were carried out on Single pixel with mesa sizes of 100 × 100 – 700 × 700 μm photodiodes. Temperature dependent dark current with corresponding R0A resistance values are reported.

This paper presents one-dimensional numerical simulations and analytical modeling of InAs nBn detectors having n-type barrier layers with donor concentrations ranging from 1.8×10¹⁵ to 2.5×10¹⁶ cm^-3. We consider only “ideal” defect-free nBn detectors, in which dark current is due only to the fundamental mechanisms of Auger-1 and radiative recombination. We employ a simplified nBn geometry, with the absorber layer (AL) and contact layer (CL) having the same donor concentration and comparable thicknesses, to reveal more clearly the underlying device physics and operation of this novel infrared detector. Our simulations lead to a new model for the ideal nBn with an n-type barrier layer (BL) that consists of two ideal backto- back photodiodes connected by a voltage-dependent series resistance representing hole conduction within the BL. Increasing the BL donor concentration lowers exponentially the hole concentration in the BL, thereby exponentially increasing the BL series resistance. Reductions in dark current and photocurrent due to the valence band barrier in the n-type BL only become appreciable when the BL series resistance becomes comparable to or exceeds the sum of the diffusion current resistances of the AL and CL. This new model elucidates the overwhelming importance of the electrical type and doping concentration of the BL to the operation of the nBn detector.

Recently, a new strategy used to achieve high operation temperature (HOT) infrared photodetectors including III-V compound materials (bulk materials and type-II superlattices) and cascade devices has been observed. Another method to reduce detector’s dark current is reducing volume of detector material via a concept of photon trapping detector. The barrier detectors are designed to reduce dark current associated with Shockley-Read (SR) processes and to decrease influence of surface leakage current without impeding photocurrent (signal). In consequence, absence of a depletion region in barrier detectors offers a way to overcome the disadvantage of large depletion dark currents. So, they are typically implemented in materials with relatively poor SR lifetimes, such as all III-V compounds. From considerations presented in the paper results that despite numerous advantages of III-V barrier detectors over present-day detection technologies, including reduced tunneling and surface leakage currents, normal-incidence absorption, and suppressed Auger recombination, the promise of a superior performance of these detectors in comparison to HgCdTe photodiodes, has not been yet realized. The dark current density is higher than that of bulk HgCdTe photodiodes, especially in MWIR range. To attain their full potential, the following essential technological limitations such as short carrier lifetime, passivation, and heterostructure engineering, need to be overcome.

We report the result of a dark current measurement of a Type-II superlattice (T2SL) infrared focal plane array (FPA), which consists of a 6 μm cutoff T2SL detector array and the readout integration circuit (ROIC) ISC0903 of FLIR Systems. In order to measure the dark current of the FPA, we obtained images with different exposure times in a fully closed cold shield of 77 K. Using the temporal change rate of the output and considering the charge conversion efficiency of the ROIC, we obtained a dark current density with an average value of 4 × 10^-5 A/cm² at a bias of -100 mV. We also compare the result of the FPA dark current measurement with that of a test element group (TEG), which was a single pixel detector, fabricated by the same process as the FPA. The dark current density of the TEG was 3 × 10^-6 A/cm² at a bias of -100 mV, lower than that of the FPA. We discuss the discrepancy between the dark current densities of the FPA and the TEG.

In this paper we report on an industry first; the growth and characterization of 6" diameter indium antimonide (InSb) substrates that are suitable for use in the fabrication of MWIR focal plane infrared detectors. Results will be presented on the production of single crystal 6" InSb ingots grown by the Czochralski (Cz) technique. We will also assess the electrical quality of new 6" InSb crystals and present uniformity information on Hall mobility, resistivity and carrier level from which we will infer comparisons on the relative dark current performance of the material grown. High quality, epitaxy-ready type surfaces have been prepared and we will demonstrate how the key surface quality characteristics of roughness (<0.5nm rms), oxide thickness (<100Å) and flatness (<7 μm TTV) have been maintained across production processes that scale 4" to 6" wafer formats. We conclude by presenting our road map for the development of large area InSb substrates and describe how developments in Czochralski crystal growth and surface finishing technology will support industry's requirements to deliver higher performance, large format IR focal place array type devices.

Photodiodes based on the GaInAs/InP material system responding in the 1.3-1.7 μm wavelength range are of interest in a wide range of applications, from optical power and channel monitors in telecommunication systems through to advanced night vision imaging using large format focal plane type detectors for defense and security applications. Here we report on our results of GaInAs PIN photo detector structures grown on 2”, 3” and 4” InP substrates by low pressure Metalorganic Chemical Vapor Deposition (MOCVD) in both standard and new larger volume format reactor configurations. High quality, lattice matched InP/GaInAs epitaxial layers were grown and we demonstrate that when moving to larger platen configurations, high degree of thickness uniformity (<3%, FTIR), lattice mismatch (<0.1%, XRD) and compositional uniformity (<2 nm, PL) can be maintained. The surface quality of epitaxial wafers will be assessed by various surface analytical techniques. We also make comparisons with the performance of 2”, 3” and 4” photodetector structures grown, this demonstrating that MOCVD production processes have been successfully scaled. We conclude by discussing the material requirements for large area infrared focal plane array photodetectors and describe how MOCVD growth technology will address industry’s requirements for increasing device sizes with improved performance.

Reactive ion beam etching (RIBE) with CH₄/H₂/Ar or Cl₂/Ar and ion beam etching (IBE) with Ar has been widely used for indium-contained compound semiconductors such as InAs, InP and InSb. To improve the performance of InSb FPAs, reduction of the ion-induced defects and the surface roughness is one of the key issues. To find the optimized plasma etching method for the fabrication of InSb devices, conventional plasma etching processes were comparatively investigated. RIBE of InSb was observed to generate residual by-products such as carbide and chloride causing the degradation of devices. On the other hand, very smooth surface was obtained by etching with N₂. However, the etch rate of the N₂ etching was too slow for the application to the device fabrication. As an alternative way to solve these problems, a multi-step plasma etching process, a combination of the Ar etching and the N₂ etching, for InSb was developed. As gradually increasing the amount of N₂ gas flow during the etching process, the plasma damage causing the surface roughen decreased and consequently smoother surface close to that of N₂ RIE could be obtained. Furthermore, Raman analysis of the InSb surface after the plasma etching indicated clearly that the multi-step etching process was an effective approach in reducing the ion-induced damages on the surface.

The growing demand for short wave infrared (SWIR) sensors and cameras has focused attention on the need for lower cost optics in this infrared region. Traditional low Tg moldable glasses typically stop transmitting in the SWIR region. New low dispersion, moldable glasses have been found that transmit through 3 microns and in combination with Precision Glass Molding (PGM) can bring this enabling technology to SWIR optics. This investigation reviews the material performance for a potential moldable solution in the SWIR range. Specific attention is given toward glasses that achieve high yields during precision glass molding and are candidates for commercial success.

Next-generation infrared (IR) optical components based on chalcogenide glasses (ChGs) may include structures which benefit from the enhanced optical function offered by spatially modifying regions with a nanocrystalline phase. Such modification may be envisioned if the means by which such spatial control of crystallization can be determined using the advantages offered through three-dimensional direct laser write (DLW) processes. While ChGs are well known to have good transparency in the IR, they typically possess lower thresholds for photo- and thermally- induced property changes as compared to other glasses such as silicates. Such low thresholds can result in material responses that include photoexpansion, large thermo-optic increases, mechanical property changes, photo-induced crystallization, and ablation. The present study examines changes in ChG material response realized by exposing the material to different laser irradiation conditions in order to understand the effects of these conditions on such material property changes. Thresholds for photoexpansion and ablation were studied by varying the exposure time and power with sub-bandgap illumination and evidence of laser induced phase change were examined. Simulations were carried out to estimate the temperature increase from the irradiation and the tolerances and stability of the calculations were examined. The models suggest that the processes may have components that are non-thermal in nature.

Laser durable multiband high reflective optics can be realized by depositing densified HfO₂/SiO₂ multilayers on aluminum alloy substrates. To further understand the impact of surface finishing and cleaning on laser-induced damage of multiband high reflective optics, 1” diameter witness samples were characterized by means of spectrophotometry, atomic force microscopy, confocal laser scanning microscopy, white light interferometry, scanning electron microscopy, and laser-induced damage threshold tests performed at 1064 nm, 20 ns, 20 Hz, and near normal angle of incidence. Laser-induced damage thresholds of 12.5 J/cm² and 47 J/cm² were obtained on a stained witness and unstained witness, respectively. A two-step laser damage process was proposed based on the post-damage analysis. The results suggest that nodule defects are the limiting factor for laser-induced damage thresholds. There exists the potential in aluminum-based dielectric coated multiband reflective optics for extremely high power laser applications.

Fabrication process of arsenic-sulfide (As-S) and arsenic-selenide (As-Se) optical fibers has been improved to enhance the transmission in the mid-IR region. Typical attenuation spectrum of As-S or As-Se optical fibers shows impurities bands, such as S-H, Se-H, O-H, which limit their operation and cause the increase of the attenuation loss in the mid-IR. Precursors purification methods and glass processing were improved to minimise those impurities bands. Regarding As- S fibers, the attenuation around 2.7 μm is 0.12 dB/m and S-H concentration is lower than 0.3 ppm. In the case of As-Se fibers, the minimum of attenuation located at 6 μm is 0.2 dB/m and Se-H concentration is lower than 0.5 ppm. Efforts have been also made to improve the mechanical properties which are usually affected by several parameters such as drawing conditions or heterogeneous inclusions contained in the glass. The double-crucible method gives high quality core/clad interface and consequently increases the strength of the fiber. Inclusions consist mainly of carbon and silica particles. Those impurities enter the glass from initial precursors and are also formed by interaction with the apparatus material. Thanks to the process improvement, impurities particles are minimized and tensile strengths up to 0.32 GPa and 0.41 GPa are reached for As-Se and As-S fibers respectively.

High operating temperature (HOT) IR-detectors are a key factor to size, weight and power (SWaP) reduced IR-systems. Such systems are essential to provide infantrymen with low-weight handheld systems with increased battery lifetimes or most compact clip-on weapon sights in combination with high electro-optical performance offered by cooled IR-technology. AIM’s MCT standard n-on-p technology with vacancy doping has been optimized over many years resulting in MWIR-detectors with excellent electro-optical performance up to operating temperatures of ~120K. In the last years the effort has been intensified to improve this standard technology by introducing extrinsic doping with Gold as an acceptor. As a consequence the dark current could considerably be suppressed and allows for operation at ~140K with good e/o performance. More detailed investigations showed that limitation for HOT > 140K is explained by consequences from rising dark current rather than from defective pixel level. Recently, several crucial parameters were identified showing great promise for further optimization of HOT-performance. Among those, p-type concentration could successfully be reduced from the mid 10¹⁶ / cm³ to the lower 10¹⁵/ cm³ range. Since AIM is one of the leading manufacturers of split linear cryocoolers, an increase in operating temperature will directly lead to IR-modules with improved SWaP characteristics by making use of the miniature members of its SX cooler family with single piston and balancer technology. The paper will present recent progress in the development of HOT MWIR-detector arrays at AIM and show electro-optical performance data in comparison to focal plane arrays produced in the standard technology.

In 2012 Selex ES demonstrated High Operating Temperature (HOT) MCT detectors with 5μm cut-off wavelength and f/4 aperture operating at temperatures above 200K. These detectors are grown by Metal Organic Vapour Phase Epitaxy (MOVPE) which enables fine control over the photo-diode structure. Since 2012 Selex has created two further generations of MOVPE HOT MCT, progressively improving operability and yield. This paper presents performance data for Selex’s third generation of HOT MCT technology and describes the improvements to the diode design and materials processing that have enabled these advances. A parallel program has developed miniature Dewars with lower heatload and reduced manufacturing costs. When integrated with the latest generation of miniature linear cryo-engines the required cooler power is reduced to the region of 1W at temperatures of 200K. This paper will present example imagery from a detector operating with <1 Watt cooler input power. The combination of third generation HOT MCT, high efficiency Dewars and miniature linear coolers will allow a drastic reduction in SWAP-C for long range hand-held thermal imagers.

Over the past few years, a new type of High Operating Temperature (HOT) photon detector has been developed at SCD, which operates in the blue part of the MWIR atmospheric window (3.4 - 4.2 μm). This window is generally more transparent than the red part of the MWIR window (4.4 - 4.9 μm), and thus is especially useful for mid and long range applications. The detector has an InAsSb active layer and is based on the new "XBn" device concept, which eliminates Generation-Recombination dark current and enables operation at temperatures of 150K or higher, while maintaining excellent image quality. Such high operating temperatures reduce the cooling requirements of Focal Plane Array (FPA) detectors dramatically, and allow the use of a smaller closed-cycle Stirling cooler. As a result, the complete Integrated Detector Cooler Assembly (IDCA) has about 60% lower power consumption and a much longer lifetime compared with IDCAs based on standard InSb detectors and coolers operating at 77K. In this work we present a new large format IDCA designed for 150K operation. The 15 μm pitch 1280×1024 FPA is based on SCD's XBn technology and digital Hercules ROIC. The FPA is housed in a robust Dewar and is integrated with Ricor's K508N Stirling cryo-cooler. The IDCA has a weight of ~750 gram and its power consumption is ~ 5.5 W at a frame rate of 100Hz. The Mean Time to Failure (MTTF) of the IDCA is more than 20,000 hours, greatly facilitating 24/7 operation.

Progress on development of lead-salt thermoelectrically-cooled (TE-cooled) imaging sensors will be presented. The imaging sensor architecture has been integrated into field-ruggedized hardware, and supports the use of lead-salt based detector material, including lead selenide and lead sulfide. Images and video are from a lead selenide focal plane array on silicon ROIC at temperatures approaching room temperature, and at high frame rates. Lead-salt imagers uniquely possess three traits: (1) Sensitive operation at high temperatures above the typical ‘cooled’ sensor maximum (2) Photonic response which enables high frame rates faster than the bolometric, thermal response time (3) Capability to reliably fabricate 2D arrays from solution-deposition directly, i. e. monolithically, on silicon. These lead-salt imagers are less expensive to produce and operate compared to other IR imagers based on II-VI HgCdTe and III-V InGaAsSb, because they do not require UHV epitaxial growth nor hybrid assembly, and no cryo-engine is needed to maintain low thermal noise. Historically, there have been challenges with lead-salt detector-to-detector non-uniformities and detector noise. Staring arrays of lead-salt imagers are promising today because of advances in ROIC technology and fabrication improvements. Non-uniformities have been addressed by on-FPA non-uniformity correction and 1/f noise has been mitigated with adjustable noise filtering without mechanical chopping. Finally, improved deposition process and measurement controls have enabled reliable fabrication of high-performance, lead-salt, large format staring arrays on the surface of large silicon ROIC wafers. The imaging array performance has achieved a Noise Equivalent Temperature Difference (NETD) of 30 mK at 2.5 millisecond integration time with an f/1 lens in the 3-5 μm wavelength band using a two-stage TE cooler to operate the FPA at 230 K. Operability of 99.6% is reproducible on 240 × 320 format arrays.

Low-frequency noise has been studied in a mid-wavelength infrared InAs/GaSb type-II superlattice-based focal plane array. Low-frequency noise is observed under reverse bias but not at zero bias, even in the presence of photo-current. The magnitude of low-frequency noise was separately measured as a function of operating temperature and operation bias. The low-frequency noise is linearly correlated with the generation-recombination component of the dark current. No correlation of low-frequency noise with photo-current or diffusion dark current was found.

Recently, a new strategy used to achieve high operation temperature (HOT) infrared photodetectors including III-V compound materials (bulk materials and type-II superlattices) and cascade devices has been observed. Another method to reduce detector’s dark current is reducing volume of detector material via a concept of photon trapping detector. The barrier detectors are designed to reduce dark current associated with Shockley-Read (SR) processes and to decrease influence of surface leakage current without impeding photocurrent (signal). In consequence, absence of a depletion region in barrier detectors offers a way to overcome the disadvantage of large depletion dark currents. So, they are typically implemented in materials with relatively poor SR lifetimes, such as all III-V compounds. From considerations presented in the paper results that despite numerous advantages of III-V barrier detectors over present-day detection technologies, including reduced tunneling and surface leakage currents, normal-incidence absorption, and suppressed Auger recombination, the promise of a superior performance of these detectors in comparison to HgCdTe photodiodes, has not been yet realized. The dark current density is higher than that of bulk HgCdTe photodiodes, especially in MWIR range. To attain their full potential, the following essential technological limitations such as short carrier lifetime, passivation, and heterostructure engineering, need to be overcome.

The Interband Cascade (IC) detector with InAs/Ga(In)Sb type-II superlattice (T2-SL) absorbers is a new type of high-performance infrared photodetector that has many unique features. In this IC detector design, the T2-SL absorber is sliced into multiple thinner segments that are sandwiched between electron and hole barriers, forming one stage. Multiple stages are electrically connected in series. The asymmetric energy-band alignment and ultra-fast carrier transport channel have enabled IC detectors to operate under/near zero-bias. The large lifetime contrast and the great design flexibility make IC detectors very suitable for high temperature operations. Our effort has led to the demonstration of mid-IR single pixel devices operating up to 450 K under zero-bias. These devices achieved superior electrical performance compared to HgCdTe technology at higher operation temperatures. In this presentation, we will discuss the new developments of low-noise mid-IR IC photodetectors and their focal plane arrays. Device studies on the influence of design on their optical and electrical performance will be discussed, and the most recent technical progress is also reported.