Non-equilibrium modes of operation for infrared detectors

New modes of operation for semiconductor infrared detectors are proposed which will enable operation in the middle and far infrared with much reduced cooling requirements. The phenomena of minority carrier exclusion and minority carrier extraction are utilised to hold the carrier densities in narrow-gap semiconductors close to their extrinsic values, at temperatures where they are normally intrinsic. Experimental results showing improved responsivity and detectivity from middle waveband devices operating at near ambient temperature confirm the principle of this new approach.     

Thermophysics modeling of an infrared detector cryochamber for transient operational scenario

An infrared detector (IR) is essentially a transducer capable of converting radiant energy in the infrared regime into a measurable form. The benefit of infrared radiation is that it facilitates viewing objects in dark or through obscured conditions by detecting the infrared energy emitted by them. One of the most significant applications of IR detector systems is for target acquisition and tracking of projectile systems. IR detectors also find widespread applications in the industry and commercial market. The performance of infrared detector is sensitive to temperatures and performs best when cooled to cryogenic temperatures in the range of nearly 120 K. However, the necessity to operate in such cryogenic regimes increases the complexity in the application of IR detectors. This entails a need for detailed thermophysics analysis to be able to determine the actual cooling load specific to the application and also due to its interaction with the environment. This will enable design of most appropriate cooling methodologies suitable for specific scenarios. The focus of the present work is to develop a robust thermo-physical numerical methodology for predicting IR cryochamber behavior under transient conditions, which is the most critical scenario, taking into account all relevant heat loads including radiation in its original form. The advantage of the developed code against existing commercial software (COMSOL, ANSYS, etc.), is that it is capable of handling gas conduction together with radiation terms effectively, employing a ubiquitous software such as MATLAB. Also, it requires much smaller computational resources and is significantly less time intensive. It provides physically correct results enabling thermal characterization of cryochamber geometry in conjunction with appropriate cooling methodology. The code has been subsequently validated experimentally as the observed cooling characteristics are found to be in close agreement with the results predicted using the developed model thereby proving its efficacy.     

Uncooled MWIR and LWIR photodetectors in Poland

The history, status, and recent progress in the middle and long wavelength Hg_1−xCd_xTe infrared detectors operating at near room temperatures are reviewed. Thermal generation of charge carriers in narrow gap semiconductor is a major limitation or sensitivity. Cooling is a straightforward way to suppress thermal generation of charge carriers and reduce related noise. However, at the same time, cooling requirements make infrared systems bulky, heavy, and inconvenient in use. A number of concepts to improve performance of photodetectors operating at near room temperatures have been proposed and implemented. Recent considerations of the fundamental detector mechanisms suggest that near perfect detection can be achieved without the need for cryogenic cooling. This paper, to a large degree, is based on the research, development, and commercialization of uncooled HgCdTe detectors in Poland. The devices have been based on 3D-variable band gap and doping level structures that integrate optical, detection and electric functions in a monolithic chip. The device architecture is optimized for the best compromise between requirements of high quantum efficiency, efficient and fast collection of photogenerated charge carriers, minimized thermal generation, reduced parasitic impedances, wide linear range, wide acceptance angles and other device features. Recent refinements in the devices design and technology have lead to sensitivities close to the background radiation noise limit, extension of useful spectral range to > 16 μm wavelength and picosecond range response times. The devices have found numerous applications in various optoelectronic systems. Among them there are fast scan FTIR spectrometers developed under MEMFIS project.     

History of infrared detectors

This paper overviews the history of infrared detector materials starting with Herschel??s experiment with thermometer on February 11^th, 1800. Infrared detectors are in general used to detect, image, and measure patterns of the thermal heat radiation which all objects emit. At the beginning, their development was connected with thermal detectors, such as thermocouples and bolometers, which are still used today and which are generally sensitive to all infrared wavelengths and operate at room temperature. The second kind of detectors, called the photon detectors, was mainly developed during the 20^th Century to improve sensitivity and response time. These detectors have been extensively developed since the 1940??s. Lead sulphide (PbS) was the first practical IR detector with sensitivity to infrared wavelengths up to ??3 ??m. After World War II infrared detector technology development was and continues to be primarily driven by military applications. Discovery of variable band gap HgCdTe ternary alloy by Lawson and co-workers in 1959 opened a new area in IR detector technology and has provided an unprecedented degree of freedom in infrared detector design. Many of these advances were transferred to IR astronomy from Departments of Defence research. Later on civilian applications of infrared technology are frequently called ??dual-use technology applications.?? One should point out the growing utilisation of IR technologies in the civilian sphere based on the use of new materials and technologies, as well as the noticeable price decrease in these high cost technologies. In the last four decades different types of detectors are combined with electronic readouts to make detector focal plane arrays (FPAs). Development in FPA technology has revolutionized infrared imaging. Progress in integrated circuit design and fabrication techniques has resulted in continued rapid growth in the size and performance of these solid state arrays.     

Terahertz and infrared photodetectors based on multiple graphene layer and nanoribbon structures

We consider new concepts of terahertz and infrared photodetectors based on multiple graphene layer and multiple graphene nanoribbon structures and we evaluate their responsivity and detectivity. The performance of the detectors under consideration is compared with that of photodetectors made of the traditional structures. We show that due to high values of the quantum efficiency and relatively low rates of thermogeneration, the graphene-based detectors can exhibit high responsivity and detectivity at elevated temperatures in a wide radiation spectrum and can substantially surpass other detectors. The detector being discussed can be used in different wide-band and multi-colour terahertz and infrared systems.     

Near‐room‐temperature photon‐noise‐limited quantum well infrared photodetector

With the modern development of infrared laser sources such as broadly tunable quantum cascade lasers and frequency combs, applications of infrared laser spectroscopy are expected to become widespread. Consequently, convenient infrared detectors are needed, having properties such as fast response, high efficiency, and room‐temperature operation. This work investigated conditions to achieve near‐room‐temperature photon‐noise‐limited performance of quantum well infrared photodetectors (QWIPs), in particular the laser power requirement. Both model simulation and experimental verification were carried out. At 300 K, it is shown that the ideal performance can be reached for typical QWIP designs up to a detection wavelength of 10 µm. At 250 K, which is easily reachable with a thermoelectric Peltier cooler, the ideal performance can be reached up to 12 µm. QWIPs are therefore suitable for detection and sensing applications with devices operating up to or near room temperature.     

Exploring novel methods to achieve sensitivity limits for high operating temperature infrared detectors

A review of high operating temperature (HOT) infrared (IR) photon detector technology vis-a-vis material requirements, device design and state of the art achieved is presented in this article. The HOT photon detector concept offers the promise of operation at temperatures above 120 K to near room temperature. Advantages are reduction in system size, weight, cost and increase in system reliability. A theoretical study of the thermal generation–recombination (g–r) processes such as Auger and defect related Shockley Read Hall (SRH) recombination responsible for increasing dark current in HgCdTe detectors is presented. Results of theoretical analysis are used to evaluate performance of long wavelength (LW) and mid wavelength (MW) IR detectors at high operating temperatures.     

Heterostructure infrared photovoltaic detectors

HgCdTe remains the most important material for infrared (IR) photodetectors despite numerous attempts to replace it with alternative materials such as closely related mercury alloys (HgZnTe, HgMnTe), Schottky barriers on silicon, SiGe heterojunctions, GaAs/AlGaAs multiple quantum wells, InAs/GaInSb strained layer superlattices, high temperature superconductors and especially two types of thermal detectors: pyroelectric detectors and silicon bolometers. It is interesting, however, that none of these competitors can compete in terms of fundamental properties. In addition, HgCdTe exhibits nearly constant lattice parameter which is of extreme importance for new devices based on complex heterostructures. The development of sophisticated controllable vapour phase epitaxial growth methods, such as MBE and MOCVD, has allowed fabrication of almost ideally designed heterojunction photodiodes. In this paper, examples of novel devices based on heterostructures operating in the long wavelength, middle wavelength and short wavelength spectral ranges are presented. Recently, more interest has been focused on p–n junction heterostructures. As infrared technology continues to advance, there is a growing demand for multispectral detectors for advanced IR systems with better target discrimination and identification. HgCdTe heterojunction detectors offer wavelength flexibility from medium wavelength to very long wavelength and multicolour capability in these regions. Recent progress in two-colour HgCdTe detectors is also reviewed.     

HOT infrared photodetectors

At present, uncooled thermal detector focal plane arrays are successfully used in staring thermal imagers. However, the performance of thermal detectors is modest, they suffer from slow response and they are not very useful in applications requiring multispectral detection. Infrared (IR) photon detectors are typically operated at cryogenic temperatures to decrease the noise of the detector arising from various mechanisms associated with the narrow band gap. There are considerable efforts to decrease system cost, size, weight, and power consumption to increase the operating temperature in so-called high-operating-temperature (HOT) detectors. Initial efforts were concentrated on photoconductors and photoelectromagnetic detectors. Next, several ways to achieve HOT detector operation have been elaborated including non-equilibrium detector design with Auger suppression and optical immersion. Recently, a new strategies used to achieve HOT detectors include barrier structures such as nBn, material improvement to lower generation-recombination leakage mechanisms, alternate materials such as superlattices and cascade infrared devices. Another method to reduce detector’s dark current is reducing volume of detector material via a concept of photon trapping detector. In this paper, a number of concepts to improve performance of photon detectors operating at near room temperature are presented. Mostly three types of detector materials are considered — HgCdTe and InAsSb ternary alloys, and type-II InAs/GaSb superlattice. Recently, advanced heterojunction photovoltaic detectors have been developed. Novel HOT detector designs, so called interband cascade infrared detectors, have emerged as competitors of HgCdTe photodetectors.     

Passivation techniques for InAs/GaSb strained layer superlattice detectors

InAs/(In,Ga)Sb Strained Layer Superlattices (SLSs) have made significant progress since they were first proposed as an infrared (IR) sensing material more than three decades ago. The basic material properties of SLS provide a prospective benefit in the realization of IR imagers with suppressed interband tunneling and Auger recombination processes, as well as high quantum efficiency and responsivity. With scaling of single pixel dimensions, the performance of focal plane arrays is strongly dependent on surface effects due to the large pixels’ surface/volume ratio. This article discusses the cause of surface leakage currents and various approaches of their reduction including dielectric passivation, passivation with organic materials (polyimide or various photoresists), passivation by overgrowth of wider bandgap material, and chalcogenide passivation. Performance of SLS detectors passivated by different techniques and operating in various regions of infrared spectrum has been compared.     

Recent Advancements in Ln‐Ion‐Based Upconverting Nanomaterials and Their Biological Applications

Upconversion nanoparticles (UCNPs) convert low‐energy infrared (IR) or near‐infrared (NIR) photons into high‐energy emission radiation ranging from ultraviolet to visible through a photon upconversion process. In comparison to conventional fluorophores, such as organic dyes or semiconductor quantum dots, lanthanide‐ion‐doped UCNPs exhibit high photostability, no photoblinking, no photobleaching, low cytotoxicity, sharp emission lines, and long luminescent lifetimes. Additionally, the use of IR or NIR for excitation in such UCNPs reduces the autofluorescence background and enables deeper penetration into biological samples due to reduced light scattering with negligible damage to the samples. Because of these attributes, UCNPs have found numerous potential applications in biological and medicinal fields as novel fluorescent materials. Different upconversion mechanisms commonly observed in UCNPs, various methods that are used in their synthesis, and surface modification processes are discussed. Recent applications of Ln‐UCNPs in the biological and medicinal fields, including in vivo and in vitro biological imaging, multimodal imaging, photodynamic therapy, drug delivery, and antibacterial activity, are also presented.     

Spherical warm shield design for infrared imaging systems

The F-number matching is the primary means to suppress stray radiation for infrared imaging systems. However, it is difficult to achieve exact F-number matching, owing to the restriction from detectors, or multiple F-number design. Hence, an additional shield is required to block the certain thermal radiation. Typical shield is called flat warm shield, which is flat and operates at room temperature. For flat warm shield, it cannot suppress stray radiation while achieving F-number matching. To overcome the restriction, a spherical reflective warm shield is required. First of all, the detailed theory of spherical warm shield design is developed on basis of the principle that stray radiation cannot directly reach the infrared focal plane array. According to the theory developed above, a polished spherical warm shield, whose radius is 18 mm, is designed to match an F/2 infrared detector with an F/4 infrared imaging system. Then, the performance and alignment errors of the designed spherical warm shield are analyzed by simulation. Finally, a contrast experiment between the designed spherical warm shield and two differently processed flat warm shields is performed in a chamber with controllable inside temperatures. The experimental results indicate that the designed spherical warm shield cannot only achieve F-number matching but suppress stray radiation sufficiently. Besides, it is demonstrated that the theory of spherical warm shield design developed in this paper is valid and can be employed by arbitrary infrared imaging systems.     

UP-conversion of terahertz radiation induced by photon drag effect

An all-optical approach to convert terahertz radiation (THz, wavelength λ₁) into infrared (IR, peak wavelength λ₂) is presented. We show that this up-conversion process is due to the photon drag effect induced by the THz radiation in intrinsic narrow-gap semiconductors followed by spatial redistribution of current carriers and band-to-band radiative recombination. The process results in non-selective high-speed (ns range rise/fall times) IR imaging of positive (conventional luminescence) and/or negative (negative luminescence) contrasts. Estimates made for an InSb pixelless converter at 300 K and moderate THz intensity (kW/cm²) show that this up-conversion process (with λ₁/λ₂>10²) can be observed with a conventional thermal imaging camera.     

Enhanced photon harvesting in silicon multicrystalline solar cells by new lanthanide complexes as light concentrators

Four europium complexes with enhanced luminescent properties have been synthesized. Thin transparent films of the complexes were prepared on glass panes and then were examined as efficient luminescent solar concentrators for full spectrum utilization in crystalline silicon photovoltaic cells. The complexes could behave as efficient solar concentrators since they absorb UV light, where the spectral response of the crystalline silicon solar cells is low and they emit at 615 nm where the spectral response is maximum. The glass panes covered with europium complexes act as planar waveguides of the emitted light that is collected by the solar cells, which are attached to the edges of the solar concentrators. The europium complexes as solar concentrators were examined in terms of the optimum concentrations and the number of coatings, which were determined in order to evaluate the maximum performance of the solar cells. The case of multiple glass panes with europium complexes was also examined while a 28% maximum increase in the photocurrent was finally established.     

Infrared radiation detector interrogated by optical frequency-domain reflectometer

We experimentally demonstrated a fast infrared (IR) radiation sensor. It is capable of measuring IR radiation independently from the environmental temperature fluctuations. Experimental work shows that this IR detection prototype have strong conveniences (fast response and reliability in harsh environment) compared to previous detectors which makes it a very good option for early fire detection systems.     

Monocrystalline ZnSe as an ionising radiation detector operated over a wide temperature range

This work presents an analysis of the main requirements for semiconductor detectors of ionising radiation that can be operated over a wide temperature range. The analysis shows that wide-gap semiconductors with a band gap greater than 2.0 eV are a better option for effective detection of ionising radiation at high temperatures. The results of an experimental investigation into the luminescent, electrical and spectrometric properties of the wide-gap semiconductor ZnSe are shown as an example. Undoped monocrystalline ZnSe has an extremely low leakage current over a wide range of temperatures up to 167 °C and can be used as a radiometric X-ray detector in pulse-counting mode over a wide temperature range up to at least 130 °C.     

Comparison studies of infrared photodetectors with a quantum-dot and a quantum-wire base

This paper mainly presents a theoretical analysis for the characteristics of quantum dot infrared photodetectors (QDIPs) and quantum wire infrared photodetectors (QRIPs). The paper introduces a unique mathematical model of solving Poisson’s equations with the usage of Lambert W functions for infrared detectors’ structures based on quantum effects. Even though QRIPs and QDIPs have been the subject of extensive researches and development during the past decade, it is still essential to implement theoretical models allowing to estimate the ultimate performance of those detectors such as photocurrent and its figure-of-merit detectivity vs. various parameter conditions such as applied voltage, number of quantum wire layers, quantum dot layers, lateral characteristic size, doping density, operation temperature, and structural parameters of the quantum dots (QDs), and quantum wires (QRs). A comparison is made between the computed results of the implemented models and fine agreements are observed. It is concluded from the obtained results that the total detectivity of QDIPs can be significantly lower than that in the QRIPs and main features of the QRIPs such as large gap between the induced photocurrent and dark current of QRIP which allows for overcoming the problems in the QDIPs. This confirms what is evaluated before in the literature. It is evident that by increasing the QD/QR absorption volume in QDIPs/QRIPs as well as by separating the dark current and photocurrents, the specific detectivity can be improved and consequently the devices can operate at higher temperatures. It is an interesting result and it may be benefit to the development of QDIP and QRIP for infrared sensing applications.     

Negative resistance with Auger suppression in near-intrinsic,low-bandgap photo-diode structures

The theory of PIN diodes made with narrow band gap material possessing appreciable Auger generation processes predicts negative resistance effects in reverse bias, accompanied by Auger suppression. The presence of moderate impurity concentrations in the intrinsic region can modify the behaviour so that a complete family of Auger-suppressed devices is revealed with interesting variations in the modes of operation. Practical IR detectors and other devices will require heterostructure technology to minimise contact generation currents.     

金属-介质-金属渔网超表面结构调控的荧光辐射：空间选择性激发和双增强

增强荧光辐射在生物成像、高灵敏探测、集成光源等方面都具有重要的应用价值.金属纳米颗粒的周围或者金属纳米结构的间隙都可以产生强的电磁场,相应的,这些结构附近的局域态密度也被极大地增强.虽然增强荧光辐射已经在多种金属纳米颗粒和颗粒对中被证明,但是利用金属纳米结构对荧光分子的吸收和辐射过程同时进行调制仍然是一个有挑战的问题.本文研究了金属-介质-金属超表面对荧光辐射的调控,其中局域表面等离激元(LSP)和磁等离激元(MPP)分別与于分子的吸收和辐射过程发中耦合相互作用.对于吸收过程,LSP的耦合作用使得可以通过旋转泵浦激光的偏振态来实现荧光分子的空间选择激发.此外,MPP模式的偏振依赖特性使得矩形渔网结构中的荧光分子的辐射波长和偏振态也受到调控.实验观测结果经过了时域有限差分模拟的验证.本文报道的纳米结构在光辐射器件和纳米尺度集成光源等方面都具有潜在的应用价值.     

Solid state detectors for neutron radiation monitoring in fusion facilities

The purpose of this communication is to summarize the main solid state based detectors proposed for neutron diagnostic in fusion applications and their applicability under the required harsh conditions in terms of intense radiation, high temperature and available space restrictions. Activation systems, semiconductor based detectors, luminescent materials and Cerenkov fibre optics sensors (C-FOS) are the main devices that are described.