Infrared multispectral imaging is attracting great interest with the increasing demand for sensitive, low-cost and scalable devices that can distinguish coincident spectral information. However, the widespread use of such detectors is still limited by the high cost of epitaxial semiconductors. In contrast, the solution processability and wide spectral tunability of colloidal quantum dots (CQDs) have inspired various inexpensive, high-performance optoelectronic devices. Here, we demonstrate a two-terminal CQD dual-band detector, which provides a bias-switchable spectral response in two distinct bands. A vertical stack of two rectifying junctions in a back-to-back diode configuration is created by engineering a strong and spatially stable doping process. By controlling the bias polarity and magnitude, the detector can be rapidly switched between short-wave infrared and mid-wave infrared at modulation frequencies up to 100 kHz with D* above 1010 jones at cryogenic temperature. The detector performance is illustrated by dual-band infrared imaging and remote temperature monitoring. Colloidal quantum dot detectors, switchable between short-wave infrared and mid-wave infrared, are demonstrated.

Dual-band infrared imaging using stacked colloidal quantum dot photodiodes

In recent years, AIM has established molecular beam epitaxy growth of mercury cadmium telluride (MCT) on GaAs substrates for the cost-effective production of standard infrared (IR)-detectors in the mid-wave infrared (MWIR) spectral range. The most recent progress in development is to apply this technology to the fabrication of 3rd generation IR-modules. The growth of MCT multi-layers with high homogeneity in layer thickness and composition, coupled with a low defect density, is the basis of high performance multi-color IR-detectors. Applying this technology to 3rd generation IR-modules, AIM is developing short-wave/mid-wave (SW/MW) and mid-wave/mid-wave (MW/MW) infrared bispectral MCT detectors with 320 × 256 pixels and a 30 μm pitch. The sensitivity of two different IR wavelengths in one detector greatly enhances the ability to gather information from a scene, which is a significant additional benefit for IR systems. In particular, the combination of the SWIR/MWIR or MWIR/MWIR spectral bands promote an enhanced target discrimination and identification by increasing the identification range, by enabling the target acquisition in front of strongly structured backgrounds, or of targets with low thermal signature. Results will be presented on AIM’s SW/MW, as well as MW/MW bispectral MCT IR detectors. The detectors demonstrate very low color cross-talk, low defect densities, thermal resolution of about 20 mK, and high quantum efficiencies.

MCT-Based High Performance Bispectral Detectors by AIM

Bispectral infrared-sensors that provide detection in two different spectral regions, e.g. short-wavelength infrared and mid-wavelength infrared (SWIR/MWIR) or MWIR/MWIR, offer compared to single-color sensors improved performance in a wide variety of space and ground-based applications. Possible applications are target identification, signature recognition and clutter rejection. In particular the combination of the SWIR/MWIR or MWIR/MWIR spectral regions promote an enhanced target discrimination and identification by increasing the identification range, by enabling the target acquisition in front of strongly structured backgrounds or of targets with low thermal signature. We have extended our MBE growth technology, primarily developed for the cost-effective production of standard IR-detectors in the MWIR spectral range, to the growth of mercury-cadmium-telluride (MCT) multi-layers with different cutoffwavelengths. The design of the bispectral pixel with two indium bumps per cell allows for temporal and spatial coincidence. To demonstrate the capabilities of the bispectral IR sensors, FPAs with a format of e.g. 320x256 pixels and a 30 μm pitch have been fabricated. In this paper we present the key performance parameters of recently optimized SWIR/MWIR and MWIR/MWIR bispectral MCT detectors along with images taken with the bispectral detectors by using SWIR or MWIR optics. The detectors demonstrate improved quantum efficiency, very low color cross-talk, and an excellent NETD in conjunction with low defect densities. Processing of the bispectral images with algorithms for combining the information from both spectral ranges provide striking evidence for the potential of these bispectral detectors in various applications.

Discovering the difference: bispectral MCT-based detectors by AIM

In recent years enormous development progress on key subcomponents of IR-modules was achieved: the operating temperature of MWIR FPAs has successfully been increased to high operating temperature (HOT) while preserving a 5μm cutoff-wavelength and small pixel pitch and miniature cryocoolers with low power consumption were introduced at AIM. This leads to new ultra-compact IR-solutions and improvements of existing IR-modules best suited to respond to the wide range of system needs in military and civilian applications. Key enabler for the realization of a low SWaP MWIR engine in a XGA, 10μm pitch format is AIM’s HOT MCT p-on-n detector technology, able to provide high electro-optical (e/o) performance at 160K. This technology has now been optimized and transferred to various detector formats and pitch sizes in the range from 10μm to 30μm. At moderate operating temperatures around 100K it can be used to provide highest e/o-performance including a very low defective pixel level. To improve thermal resolution of 640×512, 15μm pitch LWIR modules the charge handling capacity (CHC) of the associated ROIC has now been increased to nearly 20Me- . Typical integration times remain below 1ms ensuring high frame rates of 120Hz. In addition, an interlaced mode allows for an even higher CHC value of ~40Me- , a 2×2 binning mode for 450Hz operation in a smaller format. Furthermore, an optimized ROIC design in a 1024×768 format, offering a high CHC of ~7.5Me- in a small pixel pitch of 10μm, has been completed to improve existing MWIR modules and to provide a good basis for a XGA 10μm pitch LWIR version currently under development at AIM. In this paper latest performance results of improved MCT MWIR and LWIR detector arrays will be presented, together with optimization of associated cooled IR-modules.

Improved high performance MCT MWIR and LWIR modules

Progress on infrared bispectral MCT detectors towards high operating temperature and small pixel pitch

Current development efforts in IR-module technology show two major trends: Reduction in size, weight and power dissipation of IR-systems and further increase in system performance by introducing 3rd Gen IR-modules. Concerning 3rd Gen IR-modules AIM is developing SWIR/MWIR and MWIR/MWIR bispectral MCT detectors making use of its established and qualified MBE technology based on the growth of MCT multi-layers on GaAs substrates. The advantage of multispectral versus single color IR-sensors is the ability to combine sensitivity of two different IR wavelengths in one detector. This greatly enhances the ability to gather information from a scene, which is a significant additional benefit for IR-systems, for applications such as seeker heads, missile warners or counter measures against laser-guided beam-rider weapons. In particular, the combination of the SWIR/MWIR or MWIR/MWIR spectral bands promote an enhanced target discrimination and identification via increased identification range, achieved by enabling the target acquisition in front of cluttered backgrounds or of targets with low thermal signature. The information of the SWIR spectral range, which detects mainly the reflected part of the spectrum, and the passive IR-detection in the MWIR spectral range, can be favorably combined for the data acquisition and subsequent image data processing in our bispectral approach due to its temporal and spatial coincidence of the scene image. In this paper results will be presented of AIM’s SWIR/MWIR, as well as MWIR/MWIR bispectral MCT detectors with 320x256 pixels and a 30 μm pitch. The detectors demonstrate very low color cross-talk, and an excellent NETD in conjunction with low defect densities.

High-performance SWIR/MWIR and MWIR/MWIR bispectral MCT detectors by AIM

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High-performance SWIR/MWIR and MWIR/MWIR bispectral MCT detectors by AIM

Discovering the difference: bispectral MCT-based detectors by AIM