Handbook of II-VI Semiconductor-Based Sensors and Radiation Detectors

IR photodetectors play an important role in our life. They are widely used in areas such as military and space technology, night vision, astronomy, medicine, climatology, optical communications, etc. This chapter in the first part gives an overview of these devices, which are divided into two main groups – thermal detectors and photon detectors. The chapter lists the parameters that characterize these devices and gives their comparison, including their advantages and disadvantages. The materials used for the manufacture of IR detectors and the role of the atmosphere in the operation of IR detectors are also considered.

This chapter provides data about photoconductive and photovoltaic infrared detectors manufactured from HgCdTe, as well as from the alternative ternary alloy systems, such as HgZnTe and HgMnTe. Their design, performance, advantage, and disadvantages are evaluated and compared. Infrared photon detectors operating in the middle (3–5 μm) and long wavelength (8–14 μm) infrared spectral range require cryogenic cooling to achieve useful performance. Background-limited performance is typically not achieved without significant cooling of the IR photon detectors. At the same time, there are known some concepts of the high operating temperature photon detection proposed and implemented to improve the performance of IR photodetectors near room temperature, which will also be described in this chapter. The characteristics of the photoconductive and photovoltaic infrared detectors, which are produced by the leading manufacturers in this field, are presented in this chapter.

Recent advances in II–VI compound semiconductor heteroepitaxial growth and processing technologies have heavily benefitted the development and deployment of avalanche photodiodes (APDs) possessing a low excess noise factor between 1.1 to 1.4, outstanding linear gain, and high quantum efficiency, catering to the multitude of applications straddling the nanosecond regime (e.g., active imaging or individual photon counting) to the millisecond regime (e.g., astronomy). The linear-mode APD array has its genesis in the DRS Infrared Technologies LP elucidation of single carrier (electron) multiplication leading to virtually noise-free gain eclipsing 1,000 at room temperature. In this chapter, we survey the principles, design, fabrication, and technologies, in addition to the opportunities and challenges, of II–VI compound semiconductor APDs for the infrared spectral region.

This chapter examines the features of IR detectors array, the technologies used for their manufacture and their areas of possible application. In particular, it describes the approaches used to develop thermal imaging cameras based on the Focal-Plane Arrays (FPAs). This chapter provides a comparative characteristic of the types of IR receivers, analyzes the materials used in the development of photonic IR FPAs, describes the features of the manufacture of photovoltaic HgCdTe FPAs and the specifics of the operation of cooled FPAs. The trends of FPAs development such as pixel size reduction, the increase of operating temperatures and the elaboration of monolithic FPAs are also analyzed in this chapter.

This chapter focuses on new trends in the development of photon detectors and photodetectors arrays based on them. In particular, new strategies in the development of IR photodetectors are analyzed, which include the development of detectors such as high operating temperature detectors, quantum well infrared photodetectors, type-II strained-layer superlattices, barrier detectors, multistage or cascade IR detectors, quantum dot infrared photodetectors, multicolor IR detectors, and photon trapping detectors. The possibilities of manufacturing IR detectors based on semiconductor nanowires and 2D materials are also considered. The advantages and limitations of these approaches in the development of an IR photodetector are discussed as well.

The rapid development of thermal imaging technology requires a radical improvement in the technology of infrared photodetectors in the mid wave (MWIR, 3–5 μm) and long wave (LWIR, 8–14 μm) regions of the infrared (IR) range. Today, there is an urgent need to develop MWIR and LWIR array photodetectors of the third generation, which are subject to increased requirements for photosensitive elements, in particular, for operating temperatures, weight, dimensions, and power consumption.

One of the main ways to improve the performance of such photosensitive device structures is to increase the operating temperature of cooled photosensitive layer in the photodetectors without losing temperature sensitivity and infrared image quality. This trend is directly related to the development and implementation of new photosensitive semiconductor structures that provide low dark currents and, as a result, low intrinsic noise. This is achieved through the creation of semiconductor heterostructures by epitaxial methods. Currently, work on the creation of high operating temperature focal plane array (HOT FPA) is being actively carried out by leading manufacturers of optoelectronic equipment.

Another way to improve the performance of such photosensitive device structures is the use of so-called unipolar xBn barrier structures, where x is a contact semiconductor layer of n- or p-type conductivity, B is a barrier layer, and n is an absorbing layer of n-type of conductivity.

At present, research and development of nBn structures for FPAs are carried out both on the basis of III-V and II-VI materials. In the case of II-VI materials, a semiconducting HgCdTe solid solution is used. From a fundamental point of view, HgCdTe is an ideal material for creating IR detectors.

This chapter is review the latest advances in the development and fabrication of unipolar barrier structures based on HgCdTe.

This chapter focuses on infrared sensing technology based on mercury chalcogenide (NC) nanocrystals. It begins with a discussion of methods to improve NC film conductivity and then describes the structure, operation and performance of photoconductors, phototransistors and photodiodes made with NCs. In each case, we attempt to highlight the current best performing devices. Finally, we address three emerging directions for research: light-matter coupling, focal plane arrays and intraband detectors.

Graphene is the choicest and most favorable material for the development of high-operating detectors in the ultraviolet (UV) to infrared (IR), and terahertz (THz) regimes which is a replacement for transparent indium tin oxide (ITO) material. Integration of HgCdTe with graphene and development of IR detectors have enormous potentials in military and space research applications, and permits for higher IR detection performance compared with detectors using only HgCdTe material. The hetero-interface between the graphene and the HgCdTe absorber minimizes the recombination of photogenerated carriers in the detector. The graphene layer acts as a high mobility channel that drifts away photogenerated carriers before they recombine, further improving the detector’s performance. This chapter deals with the overview of the graphene/HgCdTe-based IR detectors, their fabrication, principles, and optimization procedures for the detection of IR regimes.

In this chapter we will show how much appreciated were the electro-optical characteristics of one of the most widely used semiconductors of the II-VI family, Cadmium Telluride or CdTe. High quality single crystals with industrially appreciable dimensions have been easily obtained since the beginning of the CdTe epopee. Exploiting its very high transparency in the mid-infrared it was firstly employed as window for i.r. laser applications. Its role, as a material for developing electro-optical modulators needed for the evolution of power CO₂-based lasers, was crucial. In more modern times, with the advent of nanotechnologies, CdTe has found considerable success as a UV-Vis photodetector if used in the form of dots, ribbons, belts and, more in general, when it is possible to exploit quantum confinement in reduced dimensions. But where CdTe has been most successful is in the photovoltaic field, where solar cells and photovoltaic modules, with conversion efficiency greater than 22% and 19% respectively, have been made. To date, among thin-film technologies, CdTe-based modules occupy the first place on the market and more than 8% globally.

We will talk about this and much more in the rest of this chapter by going into the detail of the photodetectors and, mainly, of the solar cells, revealing the smartest tricks normally used to make these devices sustainable, efficient and cost-effective.

This chapter focuses on the CdSe based photodetectors ranging from visible to near-infrared (NIR) regions. Detailed emphasis is given over the carrier dynamics of the CdSe and its impact over the photodetector properties. Further, different device structures namely photoconductors, Schottky diodes, heterojunction diodes and also recent advances in hybrid photodetector devices containing CdSe as an active material is discussed. Finally, we have also outlined some potential applications of CdSe based photodetectors.

Detector is a class of devices that is used to read, sense or notice something. Among variety of detectors, photodetector (PD) is a device which is used to sense the light signals and convert them into some observable/readable form (usually electrical signals). PD technology is gaining immense attention day by day due to their broad range of applications including from daily needs to medical diagnostic equipment’s, communication to security systems and food quality as well as environmental monitoring etc. The spectral region of electromagnetic radiation that can be sense by a particular PD is chiefly dependent on the band structure of the active material in PD device. CdS is one of such active materials that is extensively used in ultra violet (UV) and visible PDs owing to suitability of its band gap. This chapter intends to describe mainly CdS based all types of PDs, their applications, various design structures, suitability of materials for UV and visible PD and performance parameters of the device in introduction section. Next, this chapter introduces the researchers to the synthesis of multifarious forms of CdS used for PD followed by the various fabrication processes for the design of high performance PDs. This includes architectures, deposition methods, and choice of electrodes etc. The performance and figures of merit (FOM) of CdS based PDs are discussed in subsequent section. This section presents the latest literature (since 2011 only) of CdS based PDs and a comparison of FOM achieved by various groups followed by a summary of the content.

In the past few decades, the photoelectronic industry has been well developed to change the life in the world. As one of important photoelectronic devices, photodetectors has attracted scientists’ intensive attention based on their potential for light detection. Based on the different semiconductors, the photodetectors are restructured and used to detect the light from ultraviolet to terahertz region. ZnTe is an important II-VI group semiconductor with the band gap of 2.26 eV, which has been widely used for ultraviolet to visible region photoelectronic devices. Herein, we summarize the ZnTe-based photodetectors. ZnTe is produced by various methods to thin films, one-dimensional nanostructures, and two-dimensional nanostructures. The impurities are induced into ZnTe to improve its optoelectronic properties. Various inorganic compounds are selected to combine with ZnTe to form core/shell heterostructures, improving the performance of ZnTe-based photodetectors. Different types of ZnTe materials can be utilized in photodetectors for designed structure. ZnTe-based can be used to detect the light at ultraviolet and visible region. The influence of shape, size, amount of impurities and the structure of detector to the performance of ZnTe-based photodetectors are studied and clarified. Moreover, the applications of ZnTe for solar cells are also concluded. In the end, the problems for ZnTe-based photodetectors are summarized. We hope this review can give the new aspect for the development of ZnTe-based photodetectors, and promote the research on ZnTe-based optoelectronic devices.

This chapter provides a comprehensive overview of recent advances in the development and fabrication of solar-blind blue-UV photodetectors based on ZnSe in various forms such as single crystals, 1D nanomaterials, epitaxial and polycrystalline films, as well as heterostructures and hybrid materials. Solar-blind blue-UV photodetectors based on wide-gap ZnSe are attractive for many applications, including UV imaging in medicine, high-speed telecommunications in free air space, air pollution monitoring, and civil applications. A summary of the basic principles of operation of photodetectors, as well as the performances of photodetectors, is given. Particular attention is paid to various design schemes of photodetectors, and photodetection mechanisms. Also, the technological approaches and designs used to manufacture high-performance photodetectors based on ZnSe are considered in detail and critically.

In recent years, zinc sulfide (ZnS), a well-known wide bandgap II-VI semiconductor, has become a promising material for optoelectronic devices. To improve optical properties, ZnS nanostructures have been synthesized with different morphologies, having a high surface-to-volume ratio and unique optical properties. Due to the wide bandgap, low cost, strong radiation hardness, and high chemical stability, ZnS is considered as one of the most promising candidate for UV detectors. Additionally, doping in ZnS lattice with different elements such as Mn and Sn can adjust the optical parameters including optical density, optical band gap energy, Urbach energy, steepness parameter, and electron-phonon interactions which make it feasible to prepare tunable and high-performance UV detectors with different cut-off wavelengths. This chapter presents a review on the state-of-art research activities in the ZnS-based photoconductors, Schottky junctions, and metal-semiconductor-metal photodetectors, discussing recent achievements and characteristics of the various ZnS-based UV detectors developed to date.

This chapter is devoted to the consideration of the specifics of using II-VI-based multicomponent alloys in the development of photodetectors of various types. It is shown that usage of multicomponent alloys gives the possibility to significantly improve the parameters of both solar cells and detectors of visible and ultraviolet radiation. In particular, based on this approach, it was possible to significantly increase the solar cells efficiency and develop selective detectors that are sensitive in the required spectral region. The use of ternary and quaternary II-VI-based alloys allows to match the lattice parameters of II-VI and III-V compounds, which is necessary for the manufacture of monolithic optoelectronic devices which use the advantages of both types of semiconductor materials. Optimization of the electrophysical and physical properties of II-VI compounds, or giving them new properties via introduction of additional components, is another direction in the study of multicomponent II-VI compounds. Implementation examples are given and advantages of various II-VI-based multicomponent alloys for specific applications are analyzed.

In recent decades, there has been great interest in the development of various devices based on 1D nanostructures, such as nanowires (NWs), nanotubes (NTs), nanoribbons (NRs) and nanobelts (NBs). Such devices also include photodetectors for the visual and UV spectral range, developed on the basis of II-VI compounds such as CdTe, CdSe, CdS, ZnSe, ZnTe, ZnS. The analysis carried out in this chapter shows that the use of 1D nanostructures instead of bulk and thin-film materials in the manufacture of photodetectors can indeed lead to an improvement in their parameters. Individual NWs photoconductive detectors, phototransistors, detectors based on heterostructures, such as core-shells, 1D axial, crossed nanowire structures, and Schottky barrier-based photodetectors were used as objects for consideration in this analysis. The photosensitivity mechanism of 1D nanostructures and the manufacturing features of 1D nanostructures-based photodetectors are also discussed in this chapter. Problems that arise during the development of photodetectors based on 1D nanostructures are also considered in this chapter.

This chapter deals with II–VI ZnS, ZnSe, and CdS quantum dots (QD) photodiodes (PDs), specializing in the ultraviolet-visible range. It covers their synthesis methods, including those for increasing transfer, QD solids, extending synthesis through microwave-assisted, and so on. It deals with passivating QDs to extend the spectrum, reducing environmental effects. Doping QDs also extend the spectrum and give more controllability. The hybrid QD PDs, including nanorod, nanowire, and nanobelt, also organic/inorganic QDs are also studied. The two-dimensional hybrid PDs such as graphene and MXene are also covered. Most of these structures are of type II heterostructures that advise the charge separation and give the best device performance. Flexible devices are also discussed.

Solution processed semiconductors are a matter of research interest due to low fabrication cost, simplicity and evolution of interesting properties during the formation of thin film. Here, we explore recent design approaches of II-VI semiconductor materials like CdS, CdTe, CdSe, ZnS, ZnTe and ZnSe. We further include some recent established applications of solution processed thin films constructed from those materials especially for the purpose of photodetection. Recent studies have been found to get interested with direct synthesis of the materials while other techniques are also being considered for different applications. The constructed film is then further studied for photodetection properties and opportunities.

Infrared imaging has been confined to a black-and-white output format in the traditional systems. Human color perception is an extremely powerful image-recognition tool which has now been made accessible in the infrared with the development of multicolor photodetectors. The HgCdTe alloy is an unique material for producing multicolor IR structures. It exhibits a wavelength cut-off proportional to the alloy composition and offer multicolor capability covering whole infrared range. As molecular beam epitaxy (MBE) and metal-organic chemical vapour deposition (MOCVD) techniques developed, considerable efforts have been directed to fabricate compound multilayer heterostructures dedicated for multicolor photodetectors.

The simplest form of the photodetectors is a p-n junction device operated under reverse bias condition. Thus, requirement of a power supply source is essential for the operation of photodetectors. Self-powered photodetectors are a class of devices which requires no external power supply for their operation. Such type of photodetectors may play crucial roles in the Internet of Things (IoTs) and optical sensor networks. Therefore, the present chapter is dedicated to present some recent developments in II-VI group semiconductor-based self-powered photodetectors. Different types of photodetector structures with their working principles have been discussed.