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In the last two decades, several new concepts for improving the performance of infrared detectors have been proposed. These new concepts particularly address the drive towards the so-called high operating temperature focal plane arrays (FPAs), aiming to increase detector operating temperatures, and as a consequence reduce the cost of infrared systems. In imaging systems with the above megapixel formats, pixel dimension plays a crucial role in determining critical system attributes such as system size, weight and power consumption (SWaP). The advent of smaller pixels has also resulted in the superior spatial and temperature resolution of these systems. Optimum pixel dimensions are limited by diffraction effects from the aperture, and are in turn wavelength-dependent. In this paper, the key challenges in realizing optimum pixel dimensions in FPA design including dark current, pixel hybridization, pixel delineation, and unit cell readout capacity are outlined to achieve a sufficiently adequate modulation transfer function for the ultra-small pitches involved. Both photon and thermal detectors have been considered. Concerning infrared photon detectors, the trade-offs between two types of competing technology-HgCdTe material systems and III-V materials (mainly barrier detectors)-have been investigated.

Investigations of antimonide-based materials began at about the same time as HgCdTe ternary alloys—in the 1950s, and the apparent rapid success of their technology, especially low-dimensional solids, depends on the previous five decades of III-V materials and device research. However, the sophisticated physics associated with the antimonide-based bandgap engineering concept started at the beginning of 1990s gave a new impact and interest in development of infrared detector structures within academic and national laboratories. The development of InAs/GaSb type-II superlattices (T2SLs) results from two primary motivations: the perceived challenges of reproducibly fabricating high-operability HgCdTe focal plane arrays (FPAs) at reasonable cost and the theoretical predictions of lower Auger recombination for type T2SL detectors compared with HgCdTe. Second motivation—lower Auger recombination should be translated into a fundamental advantage for T2SL over HgCdTe in terms of lower dark current and/or higher operating temperature, provided other parameters such as Shockley-Read-Hall (SRH) lifetime are equal. InAs/GaSb T2SL photodetectors offer similar performance to HgCdTe at an equivalent cut-off wavelength, but with a sizeable penalty in operating temperature, due to the inherent difference in SRH lifetimes. It is predicted that since the future infrared (IR) systems will be based on the room temperature operation of depletion-current limited arrays with pixel densities that are fully consistent with background- and diffraction-limited performance due to the system optics, the material system with long SRH lifetime will be required. Since T2SLs are very much resisted in attempts to improve its SRH lifetime, currently the only material that meets this requirement is HgCdTe. Due to less ionic chemical bonding, III-V semiconductors are more robust than their II-VI counterparts. As a result, III-V-based FPAs excel in operability, spatial uniformity, temporal stability, scalability, producibility, and affordability—the so-called “ibility” advantages.

Since the discovery of graphene, its applications to electronic and optoelectronic devices have been intensively and thoroughly researched. Extraordinary and unusual electronic and optical properties make graphene and other two-dimensional (2D) materials promising candidates for infrared and terahertz (THz) photodetectors. Until now, however, 2D material-based performance is lower in comparison with those of infrared and terahertz detectors existing in the global market. This paper gives an overview of emerging 2D material detectors' performance and comparison with the traditionally and commercially available ones in different applications in high operating temperature conditions. The most effective single graphene detectors are THz detectors utilizing the plasma rectification effect in the field-effect transistors. Most of the 2D layered semiconducting material photodetectors operate in the visible and near-infrared regions, and generally, their high sensitivity does not coincide with the fast response time, which limits real detector functions.

In 1959, Lawson and co-workers publication triggered development of variable band gap Hg1−xCdxTe (HgCdTe) alloys providing an unprecedented degree of freedom in infrared detector design. Over the five decades, this material system has successfully fought off major challenges from different material systems, but despite that it has more competitors today than ever before. It is interesting however, that none of these competitors can compete in terms of fundamental properties. They may promise to be more manufacturable, but never to provide higher performance or, with the exception of thermal detectors, to operate at higher temperatures.In the last two decades a several new concepts of photodetectors to improve their performance have been proposed including trapping detectors, barrier detectors, unipolar barrier photodiodes, and multistage detectors. This paper describes the present status of infrared barrier detectors. It is especially addressed to the group of III-V compounds including type-II superlattice materials, although HgCdTe barrier detectors are also included. It seems to be clear that certain of these solutions have merged as a real competitions of HgCdTe photodetectors.

Room-temperature operating means a profound reduction of volume, power consumption, and cost for infrared (IR) photodetectors, which promise a wide range of applications in both military and civilian areas, including individual soldier equipment, automatic driving, etc. Inspired by this fact, since the beginning of 1990s, great efforts have been made in the development of uncooled thermal detectors. During the last two decades, similar efforts have been devoted using IR photon detectors, especially based on photovoltaic effects. Herein, the proven technologies, which have been commercialized with a large format, like InGaAs/InP pin diodes, InAsSb barrier detectors, and high-operating-temperature HgCdTe devices, are reviewed. The newly developed technology is emphasized, which has shown unique superiority in detecting mid-wavelength and long-wavelength IR signals, such as quantum cascade photodetectors. Finally, brand-new concept devices based on 2D materials are introduced, which are demonstrated to provide additional degrees of freedom in designing and fabricating room-temperature IR devices, for example, the construction of multi-heterojunctions without introducing lattice strain, the convenient integration of optical waveguides and electronic gratings. All information provided here aims to supply a full view of the progress and challenges of room-temperature IR detectors.has its own IR radiation characteristic which contains a wealth of information. For thousands of years, people have studied the visible light as the sensory spectrum of the human eye is only 380-740 nm. But for the invisible IR, people did not know it until the British astronomer Herschel discovered it with a blackened mercury thermometer over 200 years ago, since then the IR technology had developed slowly because people were not aware of the importance of IR in the next 100 years. [1,2] During World War II, PbS IR detectors for the first time were applied on battleships as a "top-secret" instrument, thus people began to focus research on IR technology. In comparison with visible, IR technology has unique characteristics:better environmental adaptability, stronger anti-interference ability, and higher resolution capability. With advantages of working at night or in harsh weather, transmitting information securely, and identifying the camouflaged target accurately, the IR detectors have been researched and widely applied in military, national defense, bioscience, and other momentous fields. [3][4][5] In the historical development of IR photo detectors, the response spectral is being extended to longer wavelengths; the pixels of imaging have been expanded from single element to tens of millions; the operating temperatures of cooled IR detectors are being increased to be closer to room temperature. [6][7][8] Nowadays, the remote IR imaging becomes clearer; the noise-equivalent temperature difference (NETD) of IR detection systems can reach 10 mK [9] or even lower; and IR detection systems become more and more integrated. [10] However, most high-...

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