Springer Handbook of Electronic and Photonic Materials

Electrical transport through materials is a large and complex field, and in this chapter we cover only a few aspects that are relevant to practical applications. We start with a review of the semi-classical approach that leads to the concepts of drift velocity, mobility and conductivity,mobilityconductivity from which Matthiessen’s Rule is derived. A more general approach based on the Boltzmann transport equation is also discussed. We review the conductivity of metals and include a useful collection of experimental data. The conductivity of nonuniform materials such as alloys, polycrystalline materials, composites and thin films is discussed in the context of Nordheim’s rule for alloys, effective medium theories for inhomogeneous materials, and theories of scattering for thin films. We also discuss some interesting aspects of conduction in the presence of a magnetic field (the Hall effect).Hall effect We present a simplified analysis of charge transport in semiconductors in a high electric field, including a modern avalanche theory (the theory of lucky drift). The properties of low-dimensional systems are briefly reviewed, including the quantum Hall effect.

Light interacts with materials in a variety of ways; this chapter focuses on refraction and absorption. Refraction is characterized by a material’s refractiverefractive index index. We discuss some of the most useful models for the frequency dependence of the refractive index, such as those due to Cauchy, Sellmeier, Gladstone–Dale, and Wemple–DiDominico. Examples are given of the applicability of the models to actual materials. We present various mechanisms of lightlightabsorption absorption, including absorption by freefree carrier carriers,phonon phonons,exciton excitons and impurities. Special attention is paid to fundamental and excitonic absorption in disordered semiconductors and to absorption by rare earth, trivalent ions due to their importance in modern photonics. We also discuss the effect of an external electric field on absorption, and the Faraday effect. Practical techniques for determining the optical parameters ofthin film thin films are outlined. Finally, we present a short technical classification of opticalglass glasses and materials.

This chapter reviews basic concepts used in the traditional macroscopic magnetism in order to understand current and future developments of submicronic spin-based electronics where interplay of electronic and magnetic properties is crucial. Traditional magnetism is based on macroscopic observation and physical quantities are deduced from classical electromagnetism. Physical interpretations are usually made with reference to atomic magnetism where localized magneticlocalized magnetism moments and atomic physics prevail, despite the fact that standard ferromagnetic materials such as Fe, Co, and Ni are not localized-type magnets (they have extended s and localized d electronic states). While this picture might be enough to understand some aspects of traditional storage and electromechanics, it is no longer sufficient for the description of condensed matter systems with smaller length scales progressing toward the nanometer range. The precise nature of magnetism (localized, free, or itinerantitinerant magnetism like Fe, Co, and Ni transition metals) with simultaneous presence of charge and spin of carriers should be considered. In addition, when we deal with thin films or multilayers as in conventional electronics or with reduced dimensionality objects such as wires, pillars, dots, or grains, magnetic properties are expected to be different from three-dimensional conventional bulk systems.

The aggregation of instrinsic point defects (vacancies and Si interstitials) in monocrystalline silicon has a major impact on the functioning of electronic devices. While agglomeration of vacancies results in the formation of tiny holes (so-called voids, around 100 nm in size, which have almost no stress field), the aggregation of Si interstitials exerts considerable stress on the Si matrix, which, beyond a critical size, generates a network of dislocation loops around the original defect. These dislocation loops are typically microns in size. Consequently, they are much more harmful to device functioning than vacancy clusters. However, the feature size in electronic devices has now shrunk below the 100 nm scale, meaning that vacancy aggregates are also no longer acceptable to many device manufacturers.This chapter is intended to give an introduction to the properties of intrinsic point defects in silicon and the nucleation and growth of their aggregates. Knowledge in this field has grown further over the last decade. It is now possible to accurately simulate the aggregation process so that the defect behavior of semiconductor silicon can be precisely tailored to the needs of the device manufacturer. Additionally, the impact of various impurities on the aggregation process is elucidated.

Atomic diffusion in semiconductors refers to the migration of atoms, including host, dopant and impurities. Diffusion occurs in all thermodynamic phases, but the solid phase is the most important in semiconductors. There are two types of semiconductor solid phase: amorphous (including organic) and crystalline. In this chapter we consider crystalline semiconductors and describe the processes by which atoms and defects move between lattice sites. The emphasis is on describing the various conditions under which diffusion can occur, as well as the atomic mechanisms that are involved, rather than on tabulating data. For brevity’s sake, we also focus on the general features found in the principal semiconductors from Groups IV, III–V and II–VI; IV–VI and oxide semiconductors are excluded from consideration. It is not surprising that most of the data available in this field relate to the semiconductors that are technologically important – they are used to fabricate electronic and optoelectronic devices. One unavoidable consequence of this technological need is that diffusion data tend to be acquired in a piecemeal fashion.

Photoconductivity is the incremental change in the electrical conductivity of a semiconductor or insulator upon illumination. The behavior of photoconductivityphotoconductivity (PC) with photon energy, light intensity and temperature, and its time evolution and frequency dependence, can reveal a great deal about carrier generation, transportcarriertransport and recombinationrecombination processes. Many of these processes now have a sound theoretical basis and so it is possible, with due caution, to use photoconductivity as a diagnostic tool in the study of new electronic materials and devices. This chapter describes the main steady-state and transient photoconductivity techniques applied in the investigation of semiconductors whose performance is limited by the presence of localized electronic states. These materials tend to be disordereddisordered semiconductoramorphous semiconductor, and possess low carrier mobilities and short free-carrier lifetimes in comparison with crystalline silicon. They are often prepared as thin filmsthin film, and are of interest for large-area applications, for example in solar cells, display backplane transistors, photoemissive devices such as organic light-emitting diodes (OLEDs) and medical imagers. However, examples of where these techniques have been useful in the study of defective crystalline semiconductors are also given. The approach followed here is by way of an introduction to the techniques, the physics supporting them, and their applications, it being understood that readers requiring more detailed information will consult the references provided.

In this chapter, we discuss electronic properties of semiconductor interfaces. Semiconductor devices contain metal–semiconductor, insulator–semiconductor, insulator–metal, and/or semiconductor–semiconductor interfaces. The electronic properties of these interfaces determine characteristics of the device. The band structure lineup at all these interfaces is determined by one unifying concept, the continuum of interface-induced gap states (IFIGSinterface-induced gap states (IFIGS)semiconductor heterostructure). These intrinsic interface states are the wave function tails of electron states that overlap the fundamental band gap of a semiconductor at the interface; in other words, they are caused by the quantum mechanical tunneling effect. IFIGS theory quantitatively explains the experimental barrier heights of well-characterized metal–semiconductor or Schottky contacts as well as the valence-band offsets of semiconductor–semiconductor interfaces or semiconductor heterostructures. Insulators are viewed as semiconductors with wide band gaps.

This chapter surveys general theoretical concepts developed to qualitatively understand and to quantitatively describe the electrical conduction properties of disordered organic and inorganic materials. In particular, these concepts are applied to describe charge transport in amorphous and microcrystalline semiconductors and in conjugated and molecularly doped polymers. Electrical conduction in such systems is achieved through incoherent transitions of charge carriers between spatially localized states. Basic theoretical ideas developed to describe this type of electrical conduction are considered in detail. Particular attention is given to the way the kinetic coefficients depend on temperature, the concentration of localized states, the strength of the applied electric field, and the charge carrier localization length. Charge transport via delocalized states in disordered systems and the relationships between kinetic coefficients under the nonequilibrium conditions are also briefly reviewed.

Nearly all materials are dielectrics, and the measurement of their dielectric response is a very common technique for their characterisation. This chapter is intended to guide scientists and engineers through the subject to the point where they can interpret their data in terms of the microscopic and atomistic dynamics responsible for the dielectric response, and hence derive useful information appropriate to their particular needs. The focus is on the physical concepts underlying the observed behaviour and is developed from material understandable by an undergraduate student. Emphasis is placed on the information content in the data, and the limits to be placed on its interpretation are clearly identified.Generic forms of behaviour are identified using examples typical of different classes of material, rather than an exhaustive review of the literature. Limited-range charge transport is included as a special item. The theoretical concepts are developed from a basic level up to the ideas current in the field, and the points where these are controversial have been noted so that the readers can choose for themselves how far to rely on them.

Solid state ionic conductors are crucial to a number of major technological developments, notably in the domains of energy storage and conversion and in environmental monitoring (such as battery, fuel cell and sensor technologies). Solid state ionic membranes based on fast ion conductors potentially provide important advantages over liquid electrolytes, including the elimination of sealing problems improved stability and the ability to miniaturize electrochemical devices using thin films. This chapter reviews methods of optimizing ionic conduction in solids and controlling the ratio of ionic to electronic conductivity in mixed conductors. Materials are distinguished based on whether they are characterized by intrinsic versus extrinsic disorder, amorphous versus crystalline structure, bulk versus interfacial control, cation versus anion conduction and ionic versus mixed ionic–electronic conduction. Data for representative conductors are tabulated.A number of applications that rely on solid state electrolytes and/or mixed ionic–electronic conductors are considered, and the criteria used to choose such materials are reviewed. Emphasis is placed on fuel cells, sensors and batteries, where there is strong scientific and technological interest. The chapter concludes by considering how solid state ionic materials are likely to be used in the future, particularly in light of the trend for miniaturizing sensors and power sources and the interest in alternative memory devices based on memristors.

This chapter covers the field of bulk single crystals of materials used in electronics and optoelectronics. These crystals are used in both active and passive modes, that is, to produce devices directly in/on bulk-grown slices of material, or as substrates in epitaxial growth, respectively. Single-crystal material usually provides superior properties to polycrystalline or amorphous equivalents. The various bulk growth techniques are outlined, together with specific critical features, and examples are given of the types of materials, and their current typical sizes, grown by these techniques. Materials covered range from group IVs (Si, Ge, SiGe, diamond, SiC), group III–Vs (e. g., such as GaAs, InP, nitrides, etc.) group II–IVs (e. g., CdTe, ZnSe, HgCdTe (MCT), etc.) through to a wide range of oxide/halide/phosphate/borate/tungstate materials. This chapter is to be treated as a snapshot only; the interested reader is referred to the remainder of the chapters in this handbook for more specific growth and characterization details on the various materials outlined in this chapter. Neither does this chapter cover the more fundamental aspects of the growth of the particular materials covered; again the reader is referred to relevant chapters within the handbook, or to other sources of information in the general literature.

It is clear that silicon, which has been the dominant material in the semiconductor industry for some time, will carry us into the comingultra-large-scale integration (ULSI) ultra-large-scale integration (ULSIultra-large-scale integration (ULSI)system-on-a-chip (SOC)) and system-on-a-chip (SOCsystem-on-a-chip (SOC)) eras, even though silicon is not the optimum choice for every electronic device. Semiconductor devices and circuits are fabricated through many mechanical, chemical, physical, and thermal processes. The preparation of silicon single-crystal substrates with mechanically and chemically polished surfaces is the first step in the long and complex device fabrication process. In this chapter, the approaches currently used to prepare silicon materials (from raw materials to single-crystalline silicon) are discussed.

Epitaxial growth of thin films of material for a wide range of applications in electronics, optoelectronics, and magneto-optics is a critical activity in many industries. The original technique, in most instances, was liquid-phase epitaxy (LPE) as this was the simplest and often the cheapest route to producing device-quality layers. While some production processes are still based on LPE, most of the research activities and, increasingly, much of the production of electronic and optoelectronic devices is now centered on metal organic chemical vapor deposition (MOCVDmetal-organic chemical vapor deposition (MOCVD)) and molecular beam epitaxy (MBEmolecularbeam epitaxy (MBE)). These latter techniques are more versatile, although the equipment is more expensive, and can readily produce multilayer structures with atomic-layer control, which is becoming more and more fundamental to the nanoscale engineering being called upon now to produce device structures in as-grown multilayers. This chapter covers these three basic techniques, including some of their more common variants, and outlines the relative advantages and disadvantages of each of them. Some examples of growth in various materials systems of importance are also outlined for each of the three techniques.

The field of narrow bandgap II-VI semiconductors is dominated by the compound Hg_1−xCd _x Te (MCTmercury cadmium telluride (MCT)), although some Hg-based alternatives to this ternary have also been suggested. The fact that MCT is still the preeminent infrared (IRinfrared (IR)) material stems, in part, from the fact that by varying the x value material can be made to cover all the IR regions of interest. In addition, the direct band transitions are responsible for large values of absorption coefficients, allowing quantum efficiencies to approach 100%. Long minority carrier lifetimes result in low thermal noise allowing high-performance detectors to be made at the highest operating temperatures of comparable wavelengths. This chapter covers the growth of MCT by various bulk growth techniques, used mainly for first-generation infrared detectors; by liquid phase epitaxy, used mainly for second-generation infrared detectors; and by metal-organic vapor phase and molecular beam epitaxies, used mainly for third-generation infrared detectors.

Wide-bandgap II–VI compounds are been applied to optoelectronic devices, especially light-emitting devices in the short-wavelength region of visible light, because of their direct gap and suitable bandgap energies. Many methods have been extensively applied to grow high-quality films and bulk single crystals from the vapor and liquid phases.This chapter firstly discusses the basic properties and phase diagrams of wide-bandgap II–VI compounds such as ZnS, ZnO, ZnSe, ZnTe, CdSe and CdTe. Then the growth methods and recent progress in films and bulk crystal growth are reviewed. In the epitaxial growth methods, the focus is on liquid-phase epitaxy (LPEliquid phase epitaxy (LPE)), vapor-phase epitaxy (VPEvaporphase epitaxy (VPE)) containing conventional VPE, hot-wall epitaxy (HWEhot-wall epitaxy (HWE)), metalorganic chemical vapor deposition (MOCVDmetal-organic chemical vapor deposition (MOCVD)) or metalorganic phase epitaxy (MOVPEmetal-organic vapor phase epitaxy (MOVPE)), molecular-beam epitaxy (MBEmolecularbeam epitaxy (MBE)) and atomic-layer epitaxy (ALEatomic layer epitaxy (ALE)). In bulk crystal growth, two typical growth methods, chemical/physical vapor transport (CVTchemicalvapor transport (CVT)/PVTphysical vapor transport (PVT)) and Bridgman techniques, are introduced.

The aim of this chapter is to convey the basic principles of x-ray and electron diffraction, as used in the structural characterization of semiconductor heterostructures. A number of key concepts associated with radiation-material and particle-material interactions are introduced, with emphasis placed on the nature of the signal used for sample interrogation. Various modes of imaging and electron diffraction are then described, followed by a brief appraisal of the main techniques used to prepare electron-transparent membranes for TEM analysis. A number of case studies on electronic and photonic material systems are then presented in the context of a growth or device development program; these emphasize the need to use complementary techniques when characterizing a given heterostructure.

The physical bases ofsurface chemical analysis surface chemical analysis techniques are described in the context of semiconductorsemiconductoranalysis analysis. Particular emphasis is placed on the SIMSsecondaryion mass spectrometry (SIMS)semiconductorcharacterization (secondary ion mass spectrometry) technique, as this is one of the more useful tools for routine semiconductor characterization. The practical application of these methods is addressed in preference to describing the frontiers of current research.

The chapter provides a summary of the fundamental concepts that are needed to understand the heat capacity C_P, thermal conductivity κ, and thermal expansion coefficient α_L of materials. The C_P, κ, and α_L of various classes of materials, namely, semiconductors, polymers, and glasses, are reviewed, and various typical characteristics are summarized. A key concept in crystalline solids is the Debye theoryDebyetheory of the heat capacity, which has been widely used for many decades for calculating the C_P of crystals. The thermal properties are interrelated through Grüneisen’s theorem. Various useful empirical rules for calculating C_P and κ have been used, some of which are summarized. Conventional differential scanning calorimetry (DSCdifferential scanning calorimeter (DSC)thermalanalysisglass transitiontemperature) is a powerful and convenient thermal analysis technique that allows various important physical and chemical transformations, such as the glass transition, crystallization, oxidation, melting etc. to be studied. DSC can also be used to obtain information on the kinetics of the transformations, and some of these thermal analysis techniques are summarized. Temperature-modulated DSC, TMDSC, is a relatively recent innovation in which the sample temperature is ramped slowly and, at the same time, sinusoidally modulated. TMDSC has a number of distinct advantages compared with the conventional DSC since it measures the complex heat capacity. For example, the glass-transition temperature T_g measured by TMDSC has almost no dependence on the thermal history, and corresponds to an almost step life change in C_P.The new Tzero DSC has an additional thermocouple to calibrate better for thermal lags inherent in the DSC measurement, and allows more accurate thermal analysis.

Semiconductor materials and devices continue to occupy a preeminent technological position due to their importance when building integrated electronic systems used in a wide range of applications from computers, cell-phones, personal digital assistants, digital cameras and electronic entertainment systems, to electronic instrumentation for medical diagnositics and environmental monitoring. Key ingredients of this technological dominance have been the rapid advances made in the quality and processing of materials – semiconductors, conductors and dielectrics – which have given metal oxide semiconductor device technology its important characteristics of negligible standby power dissipation, good input–output isolation, surface potential control and reliable operation. However, when assessing material quality and device reliability, it is important to have fast, nondestructive, accurate and easy-to-use electrical characterization techniques available, so that important parameters such as carrier doping density, type and mobility of carriers, interface quality, oxide trap density, semiconductor bulk defect density, contact and other parasitic resistances and oxide electrical integrity can be determined. This chapter describes some of the more widely employed and popular techniques that are used to determine these important parameters. The techniques presented in this chapter range in both complexity and test structure requirements from simple current–voltage measurements to more sophisticated low-frequency noise, charge pumping and deep-level transient spectroscopy techniques.

Electrical and optical properties of crystalline semiconductors are important parts of pure physics and material science research. In addition, knowledge of parameters related to these properties, primarily for silicon and III–V semiconductors, has received a high priority in microelectronics and optoelectronics since the establishment of these industries. For control protocols, emphasis has recently been placed on novel optical measurement techniques, which have proved very promising as nondestructive and even non-contact methods. Earlier they required knowledge of the free-carrier-derived optical constants, related to the electrical conductivity at infrared frequencies, but interest in the optical constants of silicon in the visible, ultraviolet (UV) and soft-x-ray ranges has been revived since the critical dimensions in devices have become smaller.This chapter surveys the electrical (Sect. 21.2) and optical (Sect. 21.3) properties of crystalline silicon. Section 21.2 overviews the basic concepts. Though this section is bulky and its material is documented in textbooks, it seems worth including since the consideration here focuses primarily on silicon and is not spread over other semiconductors – this makes the present review self-contained. To avoid repeated citations we, in advance, refer the reader to stable courses on solidstate physics [21.1, 21.2], semiconductor physics [21.3], semiconductor optics [21.4] and electronic devices [21.5]; seminal papers are cited throughout Sect. 21.2.We realize how formidable our task is – publications on electrical and optical properties of silicon amount to a huge number of titles, most dating back to the 1980s and 1990s – so any review of this subject will inevitably be incomplete. Nevertheless, we hope that our work will serve as a useful shortcut into the silicon world for a wide audience of applied physics, electrical and optical engineering students.

Silicon-germanium is an important material that is used for the fabrication of SiGe heterojunction bipolar transistors and strained Si metal-oxide-semiconductor (MOSmetal–oxide–semiconductor (MOS)) transistors for advanced complementary metal-oxide-semiconductor (CMOScomplementary metal-oxide-semiconductor (CMOS)) and BiCMOS (bipolar CMOS) technologies. It also has interesting optical properties that are increasingly being applied in silicon-based photonic devices. The key benefit of silicon-germanium is its use in combination with silicon to produce a heterojunction. Strain is incorporated into the silicon-germanium or the silicon during growth, which also gives improved physical properties such as higher values of mobility. This chapter reviews the properties of silicon-germanium, beginning with the electronic properties and then progressing to the optical properties. The growth of silicon-germanium is considered, with particular emphasis on the chemical vapour deposition technique and selective epitaxy. Finally, the properties of polycrystalline silicon-germanium are discussed in the context of its use as a gate material for MOS transistors.

Thallium-containing III-V (Tl-III-V) and bismuth-containing III-V (III-V-Bi) alloy semiconductors were first proposed as novel functional semiconductors. They are alloys consisting of semiconductors (III-V) and semimetals (Tl-V, III-Bi), and are important materials for the fabrication of temperature-insensitive lasing wavelength laser diodes as well as long wavelength infrared (LWIR) optical devices. However, the growth conditions for alloys containing Tl and Bi are very strict and the growth windows are narrow. In this chapter, the expected properties of these semiconductors and the experimental results for the growth, characterization, and device applications are described.

This chapter is devoted to a survey of the structural, opticaloptical property and electrical propertieselectrical properties of amorphous semiconductorsamorphous semiconductor on the basis of their fundamental understanding. These properties are important for various types of applications using amorphous semiconductors.First, we review general aspects of the electronic states and defects in amorphous semiconductorsamorphous semiconductor, i. e., a-Si:H and related materials, andchalcogenide glass chalcogenide glasses, and their structural, optical and electrical properties.Further, we survey the two types of phenomena associated with amorphous structure, i. e.,light-induced phenomena light-induced phenomena, and quantum phenomena associated with nanosized amorphous structure. The former are important from the viewpoint of amorphous-siliconsolar cell solar cells. The latter phenomena promise novel applications of amorphous semiconductors from the viewpoint of nanotechnology.nanotechnology

Processes used to grow hydrogenated amorphous silicon (a-Si : H) and microcrystalline silicon (μc-Si : H) from SiH₄ and H₂ ∕ SiH₄ glow discharge plasmas are reviewed. Differences and similarities between growth reactions of a-Si : H and μc-Si : H in a plasma and on a film-growing surface are discussed, and the process of nucleus formation followed by epitaxial-like crystal growth is explained as being unique to μc-Si : H. The application of a reaction used to determine the dangling-bond defect density in the resulting a-Si : H and μc-Si : H films is emphasized, since it can provide clues about how to improve the optoelectronic properties of those materials for device applications, especially thin-film silicon-based solar cells. solar cellMaterial issues related to the realization of low-cost and high-efficiency solar cells are described, and finally recent progress in this area is reviewed.

Ferroelectric materials offer a wide range of useful properties. These include ferroelectric hysteresis (used in nonvolatile memories), high permittivities (used in capacitors), high piezoelectric effects (used in sensors, actuators and resonant wave devices such as radio-frequency filters), high pyroelectric coefficients (used in infra-red detectors), strong electro-optic effects (used in optical switches) and anomalous temperature coefficients of resistivity (used in electric-motor overload-protection circuits). In addition, ferroelectrics can be made in a wide variety of forms, including ceramics, single crystals, polymers and thin films – increasing their exploitability. This chapter gives an account of the basic theories behind the ferroelectric effect and the main ferroelectric material classes, discussing how their properties are related to their composition and the different ways they are made. Finally, it reviews the major applications for this class of materials, relating the ways in which their key functional properties affect those of the devices in which they are exploited.

Dielectrics are an important class of thin-film electronic materials for microelectronics. Applications include a wide swathe of device applications, including active devices such as transistorsmicroelectronicstransistor and their electrical isolation, as well as passive devices, such as capacitorsmicroelectronicscapacitor. In a world dominated by Si-based device technologies, the properties of thin-film dielectric materials span several areas. Most recently, these include high-permittivity applications, such as transistor gate and capacitor dielectrics, as well as low-permittivity materials, such as inter-level metal dielectrics, operating at switching frequencies in the gigahertz regime for the most demanding applications.This chapter provides a survey of the various dielectric material systems employed to address the very substantial challenge associated with the scaling Si-based integrated circuit technology. A synopsis of the challenge of device scaling is followed by an examination of the dielectric materials employed for transistors, device isolation, memory and interconnectmicroelectronicsinterconnect technologies. This is presented in view of the industry roadmap which captures the consensus for device scaling (and the underlying economics) – the International Technology Roadmap for Semiconductors.

This chapter provides an extended introduction to the basic principles of thin-film technologythin filmtechnology, including deposition processes, structure, and some optical and electrical properties relevant to this volume. The material is accessible to scientists and engineers with no previous experience in this field, and contains extensive references to both the primary literature and earlier review articles. Although it is impossible to provide full coverage of all areas or of the most recent developments in this survey, references are included to enable the reader to access the information elsewhere, while the coverage of fundamentals will allow this to be appreciated.Deposition of thin films by the main physical deposition methodsdeposition method of vacuum evaporation, molecular-beam epitaxy and sputtering are described in some detail, as are those by the chemical deposition methods of electrodeposition, chemical vapour deposition and the Langmuir–Blodgett technique. Examples of structural features of some thin filmsthin film are given, including their crystallography, larger-scale structure and film morphology. The dependence of these features on the deposition conditions are stressed, including those required for the growth of epitaxial films and the use of zone models in themorphological characteristics classification of the morphological characteristics. The main optical properties of thin films are reviewed, including the use of Fresnel coefficients at media boundaries, reflectance and transmittance, matrix methods and the application of these techniques to the design of antireflection coatings, mirrors and filters. The dependence of electrical conductivity (or resistivity) and the temperature coefficient of resistivity in metallic thin films is discussed, in particular the models of Thomson, Fuchs–Sondheimer and the grain-boundary model of Mayadas–Shatzkes. For insulating and semiconducting thin films the origin and effects of several high-field conduction processes are examined, including space-charge-limited conductivity, the Poole–Frenkel effect, hopping, tunnelling and the Schottky effect. Finally, some speculations regarding future developments are made.

Thick filmthick filmsensormicroelectronics technology is an example of one of the earliest forms of microelectronics-enabling technologies and it has its origins in the 1950s. At that time it offered an alternative approach to printed circuit board technology and the ability to produce miniature, integrated, robust circuits. It has largely lived in the shadow of silicon technology since the 1960s. The films are deposited by screen printing (stenciling), a graphic reproduction technique that can be dated back to the great Chinese dynasties of around a thousand years ago. Indeed, there is evidence that even early Palaeolithic cave paintings from circa 15000 BC may have been created using primitive stenciling techniques. With the advent of surface-mounted electronic devices in the 1980s, thick film technology again became popular because it allowed the fabrication of circuits without through-hole components.This chapter will review the main stages of thethick filmfabrication thick film fabrication process and discuss some of the commonly used materials and substrates. It will highlight the way in which the technology can be used to manufacture hybridmicroelectronic circuit microelectronic circuits. The latter stages of the chapter will demonstrate how the technology has evolved over the past twenty years or so to become an important method in the production of solid state sensors.

III–V ternary and quaternary alloy systems are potentially of great importance for many high-speed electronic and optoelectronic devices, because they provide a natural means of tuning the magnitude of forbidden gaps so as to optimize and widen the applications of such semiconductor devices. Literature on the fundamental properties of these material systems is growing rapidly. Even though the basic semiconductor alloy concepts are understood at this time, some practical and device parameters in these material systems have been hampered by a lack of definite knowledge of many material parameters and properties.This chapter attempts to summarize, in graphical and tabular forms, most of the important theoretical and experimental data on the III–V ternary and quaternary alloy parameters and properties. They can be classified into six groups:1.Structural parameters2.Mechanical, elastic, and lattice vibronic properties3.Thermal properties4.Energy band parameters5.Optical properties6.Carrier transport properties.The III–V ternary and quaternary alloys considered here are those of Group III (Al, Ga, In) and V (N, P, As, Sb) atoms. The model used in some cases is based on an interpolation scheme and, therefore, requires that data on the material parameters for the related binaries (AlN, AlP, GaN, GaP, etc.) are known. These data have been taken mainly from the Landolt-Börnstein collection, Vol. III/41, and from the Handbook on Physical Properties of SemiconductorsVolume 2: III–V Compound Semiconductors, published by Springer in 2004. The material parameters and properties derived here are used with wide success to obtain the general properties of these alloy semiconductors.

Optical, electrical, mechanical, and thermal properties of group III nitrides, inclusive of AlN, GaN, InN and their ternary and quaternary alloys, are discussed. The driving force for group III nitride semiconductors is their important applications in optoelectronics, microwave amplifiers, and high voltage power switches. Owing to the aforementioned applications, the fundamental properties of each III nitride binary, as well as the alloys that have been acquired, are discussed in this chapter. In general, an appropriate assessment of the material properties for any material is not straightforward to begin with and the nitride family is no exception, particularly considering that group III nitrides are prepared on foreign substrates as low-cost native substrates are not yet available. Understandably, precise measurements of the mechanical, thermal, electrical and optical properties of the semiconductor nitride family are imperative for further advances. Notwithstanding the great progress that has already been made to further understand and exploit group III nitrides, especially GaN, reliable data for AlN and InN are still in the state of evolution, and naturally the subject of some controversy. This is, in part, a consequence of measurements having been performed on samples of widely varying quality. When possible, the spurious discrepancies have been disregarded. For some materials, too few measurements are available to yield a consensus, in which case the available data are simply reported. Defects in group III nitrides as well as GaN-based nanostructures are also discussed.

The III-V nitridesemiconductor semiconductors, gallium nitride, aluminum nitride, and indium nitride, have been recognized as promising materials for novel electronic and optoelectronic device applications for some time now. Since informed device design requires a firm grasp of the material properties of the underlyingelectronic material electronic materials, the electron transport that occurs within these III–Vnitridesemiconductor nitride semiconductors has been the focus of considerable study over the years. In an effort to provide some perspective on this rapidly evolving field, in this paper we review analyses of the electron transport within these III–V nitride semiconductors. In particular, we discuss the evolution of the field, compare and contrast results obtained by different researchers, and survey the more recent literature. In order to narrow the scope of this chapter, we will primarily focus on the electron transport within bulk wurtzite gallium nitride, aluminum nitride, and indium nitride for the purposes of this review. Most of our discussion will focus on results obtained from our ensemble semi-classical three-valleyMonte Carlo (MC) simulation Monte Carlo simulations of theelectron transport electron transport within these materials, our results conforming with state-of-the-art III–V nitride semiconductor orthodoxy. Steady-state and transient electron transport results are presented. We conclude our discussion by presenting some recent developments on the electron transport within these materials.

Owing to their suitable band gaps and high absorption coefficients, Cd-based compounds such as CdTe and CdS are the most promising photovoltaic materials available for low-cost high-efficiency solar cells. Additionally, because of their large atomic number, Cd-based compounds such as CdTe and CdZnTe, have been applied to radiation detectors. For these reasons, preparation techniques for these materials in the polycrystalline films and bulk single crystals demanded by these devices have advanced significantly in recent decades, and practical applications have been realized in optoelectronic devices. This chapter mainly describes the application of these materials in solar cells and radiation detectors and introduces recent progress.

The main purpose of this chapter is to describe the applications and technology of II–VI narrow bandgap semiconductors, focussing on HgCdTe for infrared sensors. It provides a historical record of the development HgCdTe through photoconductors and photodiode arrays. The solid-state physics of HgCdTe is described to provide a foundation to explain the main crystal growth processes and device technologies. It concludes with a review of the research and development programs in centers around the world on third-generation infrared detector technology (so-called GEN III detectors). These include small pixel technology, higher operating temperature (HOThigher operating temperature (HOT)) device structures, two-color array technology, electron avalanche photodiodes (e-APDelectron avalanche photodiode (e-APD)s), multifunctional HgCdTe detectors, retina level processing, and future trends for HgCdTe infrared detector arrays.

Unlikesemiconductorlasermodulatordetector the majority of electronic devices, which are silicon based, optoelectronic devices are predominantly made using III–V semiconductor compounds such as GaAs, InP, GaN, and GaSb, and their alloys due to their direct-band gap. Understanding the properties of these materials has been of vital importance in the development of optoelectronic devices. Since the first demonstration of a semiconductor laser in the early 1960s, optoelectronic devices have been produced in their millions, pervading our everyday lives in communications, computing, entertainment, lighting, and medicine. It is perhaps their use in optical-fiber communications that has had the greatest impact on humankind, enabling high-quality and inexpensive voice and data transmission across the globe. Optical communications spawned a number of developments in optoelectronics, leading to devices such as vertical-cavity surface-emitting lasers, semiconductor optical amplifiers, optical modulators, and avalanche photodiodes. In this chapter, we discuss the underlying theory of operation of some important optoelectronic devices. The influence of carrier–photon interactions is discussed in the context of producing efficient and high-performance emitters and detectors. Finally, we discuss how the semiconductor band structure can be manipulated to enhance device properties using quantum confinement and strain effects, and how the addition of dilute amounts of elements such as nitrogen and bismuth is having a profound effect on the next generation of optoelectronic devices.

This chapter outlines the basic physics, chemical nature and properties of liquid crystals. These materials are important in the electronics industry as the electro-optic component of flat-panel liquid-crystal displays, which increasingly dominate the information display market.Liquid crystalsliquid crystal (LC) are intermediate states of matter which flow like liquids, but have anisotropic properties like solid crystals. The formation of a liquid-crystal phase and its properties are determined by the shape of the constituent molecules and the interactions between them. While many types of liquid-crystal phase have been identified, this Chapter focuses on those liquid crystals which are important for modern displays.The electro-optical response of a liquid crystal display (LCDliquid crystal display (LCD)liquid crystal display (LCD)) depends on the alignment of a liquid-crystal film, its material properties and the cell configuration. Fundamentals of the physics of liquid crystals are explained and a number of different displays are described.In the context of materials, the relationship between the physical properties of liquid crystals and their chemical composition is of vital importance. Materials for displays are mixtures of many liquid-crystal compounds carefully tailored to optimise the operational behaviour of the display. Our current understanding of how chemical structure determines the physical properties is outlined, and data for typical liquid-crystal compounds are tabulated. Some key references are given, but reference is also made to more extensive reviews where additional data are available.

This Chapter surveys organic photoreceptor devices used in electrophotography.electrophotography Included in the discussion are the materials (polymers, pigments, charge-transport molecules, etc.), device architecture,photoreceptordevice architecture fabrication methods, and device electrical characteristicsphotoreceptororganicphotoreceptorelectrical characteristic that are critical to the successful functioning of an electrophotographic device (printer).The Chapter is organized as follows. A brief discussion of the history of xerography and the contributions of Chester Carlson is followed by operational considerations and critical materials properties. The latter includes dark conductivity, photodischarge–charge transport, and photogeneration. Organic photoreceptor characterizations of dark decay, photosensitivity, and electrical-only cycling are discussed in detail. This is followed by discussions of photoreceptor architecture, coating technologies, substrate, conductive layer, and coated layers which carry out specific functions such as smoothing, charge blocking, charge transport, backing, and surface protection.

This chapter surveys the field of solid-state luminescent materials, beginning with a discussion of the different ways in which luminescence can be excited. The internal energy-level structures of luminescent ions and centres, particularly rare-earth ions, are then discussed before the effects of the vibrating host lattice are included. Having set the theoretical framework in place, the chapter then proceeds to discuss the specific excitation process for photo-stimulated luminescence and thermally stimulated luminescence before concluding by surveying current applications, including phosphors for compact fluorescent and LED lighting, long-term persistent phosphors, x-ray storage phosphors, and scintillators.

Photonic crystals offer a well-recognized ability to control the propagation of modes of light in an analogous fashion to the way in which nanostructures have been harnessed to control electron-based phenomena. This has led to proposals and indeed demonstrations of a wide variety of photonic-crystal-based photonic devices with applications in areas including communications, computing and sensing, for example. In such applications, photonic crystals can offer both a unique performance advantage, as well as the potential for substantial miniaturization of photonic systems. However, as this review outlines, two-dimensional (2-D) and three-dimensional (3-D) structures for the spectral region covering frequencies from the ultraviolet (UV) to the near-infrared (near-IRnear-infrared (near-IR)) (≈ 2 μm) are challenging to fabricate with appropriate precision, and in a cost-effective and also flexible way, using traditional methods. Naturally, a key concern is how amenable a given approach is to the intentional incorporation of selected defects into a particular structure. Beyond passive structures, attention turns to so-called active photonic crystals, in which the response of the photonic crystal to light can be externally changed or tuned. This capability has widespread potential in planar lightwave circuits for telecommunications, where it offers mechanisms for selective switching, for example. This review discusses alternative proposals for tuning of such photonic crystals.

This chapter reviews the principles of bandgap engineering and quantum confinement in semiconductors, with a particular emphasis on the optoelectronic properties of quantum wells. The chapter begins with a review of the fundamental principles of bandgap engineering and quantum confinement. It then describes the optical and electronic properties of semiconductor quantum wells and superlattices at a tutorial level, before describing the principal optoelectronic devices. The topics covered include edge-emitting lasers and light-emitting diodes (LEDlight-emitting diode (LED)s), resonant cavity LEDs and vertical-cavity surface-emitting lasers (VCSELvertical cavitysurface emitting laser (VCSEL)quantumcascade laser (QCL)quantum well (QW)solar cellsuperlattice (SL)avalanche photodiode (SL-APD)quantum well (QW)light modulators), quantum cascade lasers, quantum well solar cells, superlattice avalanche photodiodes, infrared detectors, and quantum well light modulators. The chapter concludes with a brief discussion of new research directions on quantum dot and nanowire structures.

Inorganic glasses form the backbone of dielectric materials in optics and photonic applications. In addition to offering a range of transparency windows, intrinsic physical properties of glass materials also offer flexibility of processing for the realization of fibers, films, and shaped optical elements. Traditionally, the main role of glass has been as an optically passive material. However, a significant attribute of glass as an optical medium is to host dopants such as nanoparticles or active ions in a unique chemical environment, which can be engineered via processing, by controlling the geometry to develop active and passive photonic devices, such as laser, amplification, storage media, optical switching, frequency conversion, and sensor media.For photonic integration, many of the attributes of glasses are particularly compelling. Glasses allow numerous options for thin film deposition and integration on arbitrary platforms. The possibility of controlling the thermal and flow properties, e. g., expansion coefficient, crystallization, and viscosity during film deposition of a glass may allow realization of extremely low-loss microphotonic waveguides, photonic crystals, and microcavities. The metastable nature of glass can enable the direct patterning of photonic elements by energetic beams.This chapter provides an overview of these unique properties of glasses, from the perspectives of the technology options they afford and the practical limitations they present. Further, an overview is provided of the main families of glassy inorganic films studied for integrated optics. Finally, the main features of rare-earth doped glasses are reviewed, with an emphasis on their potential for implementation in compact integrated light sources and amplifiers.

A brief review of optical nonlinearity in photonic glasses is given. For third-order nonlinearity, the relationship between two-photon absorption and nonlinear refractive index is considered using a formalism developed for crystalline semiconductors. Stimulated light scattering and supercontinuum generation in optical fibers and waveguides are introduced. Prominent resonant-type nonlinearity in particle-embedded glasses is described. For second-order nonlinearity, a variety of poling methods are summarized. The nonlinearity also appears in crystallized and ceramic glasses. Finally, it is pointed out that various photoinduced changes can appear when excited by linear and nonlinear optical processes.

Photovoltaic solar cells are gaining wide acceptance for producing clean, renewable electricity. This has been based on more than 40 years of research that has benefited from the revolution in silicon electronics and compound semiconductors in optoelectronics. This chapter gives an introduction into the basic science of photovoltaic solar cellssolar cell and the challenge of extracting the maximum amount of electrical energy from the available solar energy. In addition to the constraints of the basic physics of these devices, there are considerable challenges in materials synthesis. The latter has become more prominent with the need to reduce the cost of solar module manufacture as it enters mainstream energy production. The chapter is divided into sections dealing with the fundamentals of solar cells and then considering six very different materials systems, from crystalline silicon through to polycrystalline thin films and perovskites. These materials have been chosen because they are all either in production or have the prospect of being in production over the next few years. Many more materials are being considered in research and some of the more exciting, excitonic cells and nanomaterials are mentioned. However, there is insufficient space to give these very active areas of research the justice they deserve. I hope the reader will feel sufficiently inspired by this topic to read further and explore one of the most exciting areas of semiconductor science. The need for high-volume production at low cost has taken the researcher along paths not normally considered in semiconductor devices and it is this that provides an exciting challenge.

Low-temperature-thin-film semiconductorsthin filmsemiconductor and dielectrics are critical for large-area flexible electronics, including displays, smart skins and imagers. Despite the presence of structural disorder, these materials show promising electronic transport properties that are vital for devices such asthin filmtransistor (TFT) thin-film transistors (TFTthin filmtransistor (TFT)large area electronicflexible substrateamorphoussemiconducting films) and sensors. This chapter presents an overview of material and transport properties pertinent to large-area electronics on mechanically flexible substrates. We begin with a summary of process challenges for low-temperature fabrication of a-Si:H TFTs on plastic substrates, followed by a description of transport properties of amorphous semiconducting films, along with their influence on TFT characteristics. The TFTs must maintain electrical integrity under mechanical stress induced by bending of the substrates. Bending-induced changes are not limited to alteration of device dimensions and involve modulation of electronic transport of the active semiconducting layer.

Modern flat-panel x-ray imaging detectors have played an important role in the transition from analog to digital x-ray imaging. They capture an x-ray image electronically and hence enable a clinical transition to digital radiography. This chapter critically discusses the material, transport and imaging detector properties (e. g., dark current) of several potential x-ray photoconductors and compares them with an ideal photoconductor for use in direct-conversion imaging detectors. The present chapter also considers various metrics of detector performances including sensitivity, detective quantum efficiency, resolution in terms of the modulation transfer function, image lag and ghosting; and examines how these metrics depend on the photoconductor material, and detector structure and design.

Phase-change materials are Te-containing alloys, typically lying along the GeTe-Sb₂Te₃ quasibinary tie line. Their ability to switch, reversibly and extremely quickly, between the crystalline and amorphous phases, combined with the high stability of both phases, makes them ideally suitable for memory applications. They have been long used in optical data storage in the form of DVD and Blu-Ray disks and recently have also emerged as a leading candidate for electronic nonvolatile memory devices. In this chapter, a detailed description of these materials is provided starting with the global and local structures of the two phases, which were extensively studied both experimentally and using ab initio computer simulations, and followed by the discussion of possible atomistic mechanisms of the phase-change process, with special accent on the role of electronic excitation. The chapter is concluded by a brief description of the present and emerging applications of this class of chalcogenide materials.

The chapter details the underlying phenomena that underpin electronic applications that have followed from the discoveries of C₆₀ and carbon nanotubes. The reduced dimensionality of these self-organised structures, high electron mobility, weak electromigration, and the plethora of quantum electronic effects exhibited by these structures suggest they are serious candidates for molecular electronics. The detail of the surface chemistry and conditions of synthesis assume greater importance than for conventional electronic materials since all atoms are on the exterior of these structures, as is outlined with references to the wider literature. Essential electronic structure information is given with reference to the transport measurements that have contributed greatly to the evolution of the field with emphasis on the Coulomb blockade and ballistic transport phenomena. The major electronic applications are then outlined, giving the state-of-the-art figures of merit for performance and comments on prospects for realisation.

More than a decade has passed since the graphene was synthesized for the first time but still there are many applications that have not been explored. The first intended application for graphene was its high mobility property for high-speed electronics. This task became more difficult when the problem with zero bandgap of graphene made an obstacle to close the current flow of transistor. Different remedies, for example, downscaling the dimensions to nano-ribbons and bilayer structures were proposed to create a reasonable bandgap in graphene for electronic applications. The main idea was to improve the figure of merit I_on ∕ I_off for RF devices. Although many important achievements were made, but later graphene was considered as a better choice for photonic applications. For example, graphene was used as light absorber in the lateral direction for modulators, or sensitive to light in photodetectors when it is vertically illuminated. Nowadays the graphene has inaugurated a new platform in flexible and transparent electronics. As example, electronics giant producers have already integrated graphene for flexible screens.During recent years, many research efforts have been spent on other two-dimensional (2-D) crystals (transition metal dichalcogenides, silicene, and germanene) as competitors to graphene but it is still a long way to integrate such materials for industrial applications.

The purpose of this chapter is to review the current status of magnetic materials used in data storage. The emphasis is on magnetic materials used in disk drives and in the magnetic random-access memory (MRAMmagneticrandom-access memory (MRAM)) technology. A wide range of magnetic materials is essential for the advance of magnetic recording both for heads and media, including high-magnetization soft-magnetic materials for write heads, antiferromagnetic alloys with high blocking temperatures and low corrosion propensity for pinning films in giant-magnetoresistive (GMRgiant magnetoresistance (GMR)) sensors and ferromagnetic alloys with large values of giant magnetoresistance. For magnetic recording media, the advances are in high-magnetization metal alloys with large values of switching coercivity. A significant limitation to magnetic recording is found to be the superparamagnetic effect and advances have been made in multilayer ferromagnetic films to reduce the impact of the effect, but also to allow high-density recording have been developed. Perpendicular recording as compared to longitudinal recording is reviewed and it is shown that this technology will soon be replaced first by heat-assisted and later by bit-patterned magnetic recording in order to progress steadily toward areal densities well above 1012 bit ∕ in2 (1 Tbit ∕ in2 or 1000 Gbit ∕ in2). While an MRAM cell exploits some of the materials used in GMR sensors, its basic component is the magnetic tunneling junction in which magnetic films are coupled by a thin insulating film and conduction occurs by quantum mechanical tunneling. The status of MRAM cell technology and some closely related key problems are reviewed.

The discovery by J. G. Bednorz and K. A. Müller in 1986 that the superconducting state can exist in oxides at temperatures above 30 K stimulated research in the field of superconductivity and opened a new field of research. Within a few years a large number of cuprate superconductors with transition temperatures well above the boiling point of liquid nitrogen have been found. In this chapter, an overview of the major families of high-temperature superconductors and their physical properties is presented.Starting from the well-known characteristics of conventional superconductors, described in Sect. 50.1, the new phenomena observed in high-temperature superconductors are considered. The complexity of the physical properties of the cuprate superconductors is closely related to the fact that these materials are close to a metal–insulator transition. In Sects. 50.2 and 50.3, the crystal structures, the general trends for the critical temperatures, the anisotropy of the physical properties, and the factors limiting the transport critical current density are discussed. Because of their importance in the field of electronics some features of thin films are presented in Sect. 50.4.Strictly speaking, the binary compound MgB₂ is not a high-temperature superconductor. Nevertheless, an overview of the physical properties of this interesting metallic superconductor, characterized by a transition temperature as high as 39 K, has been included in the present chapter (Sect. 50.5).In 2008, H. Hosono et al. discovered that the layered superconductor La ( O_1−xF _x  ) FeAs (x = 0.11) superconducts at a temperature as high as 26 K. A maximum critical temperature of 58 K has been reported for the iron-pnictide superconductor Sm ( O_0.74F_0.26 ) FeAs. The iron-based superconductors are therefore considered as a second class of high-temperature superconductors. Their properties are described in Sect. 50.6.

The prospects of using organic materials in electronics and optoelectronics applications have attracted scientists and technologists since the 1970s. This field has become known as molecular electronics. Some successes have already been achieved, for example, the liquid-crystal display, organic light-emitting displays, and photoreceptors in electrophotography. Other products such as organic photovoltaic devices, chemical sensors and plastic transistors are developing fast. There is also a keen interest in exploiting technologies at the molecular scale that might eventually replace silicon devices. This chapter provides some of the background physics and chemistry to the interdisciplinary subject of molecular electronics. A review of some of the possible application areas for organic materials is presented and some speculation is provided regarding future directions.

Organic materials for chemical sensing are broadly classified into three categories: (i) macrocyclic compounds, (ii) conducting polymers, and (iii) cavitand molecules. A short review of current progress in inorganic sensing materials including graphene is given, pointing out their strengths and limitations. Principal wet techniques for depositing organic thin films are described and electrical, optical, and structural properties of all three types of organic materials are analyzed in relation to their importance in chemical sensing. Examples of recent advances in chemical sensing of different analytes and pollutants are presented.

This chapter is a high-level overview of the materials used in an electronic package including: metals used as conductors in the package; ceramics and glasses used as dielectrics or insulators; and polymers used as insulators and, in a composite form, as conductors. There is a need for new materials to meet the ever-changing requirements for high-speed digital and radio frequency (RFradio frequency (RF)) applications. There are different requirements for digital and RF packages that translate into the need for unique materials for each application. The interconnecting and dielectric (insulating) requirements are presented for each application and the relevant material properties and characteristics are discussed. The fundamental material characteristics of materials are: dielectric constant, dielectric loss, thermal and electric conductivity, resistivity, moisture absorption, glass transition temperature, strength, time-dependent deformation (creep), and fracture toughness. The material characteristics and properties are dependent upon how they are processed to form the electronic package, so the fundamentals of electronic packaging processes are discussed including wirebonding, solder interconnects, flip chip interconnects, underfill for flip chip and overmolding. The relevant material properties are given along with requirements (including environmentally friendly Pb-free packages) that require new materials to be developed to meet future electronics needs for both digital and RF applications.

One of the responsibilities of scientists is to help develop new ways in which we can generate energy, since gaining control over energy resources such as petroleum has been one of the main reasons for conflict between nations. Renewable energy generated by solar cells is one of the potential solutions to the problem of maintaining our energy supply and these have been studied intensively for about half-century. Today, silicon solar cells have already been commercialized and have become an indispensable source of electricity. However, the price of electricity produced by silicon solar cells is still higher than that produced by petroleum. In order to increase the production of energy by solar cells, the price of electricity produced by solar cells needs to be lower than that produced by petroleum. Organic solar cells have the potential to be part of the next generation of low-cost solar cells. There was a steep increase in the power-conversion efficiency of organic solar cells around the year 2000, indicating that the technology needed to bring them to a commercial level would be established by around 2020, taking into consideration the example of organic electroluminescent devices for which scientific breakthroughs were made in 1987 and commercialization occurred around 2010. Now, in 2015, the power-conversion efficiency of organic solar cells has reached 12%.Organic solar cells have many advantages; they are flexible, printable, light weight, and low cost, can be fashionably designed, and can be fabricated by roll-to-roll production, etc. Printed organic solar cells can be attached to the roofs, windows, and walls of houses and buildings. Automobiles wrapped with colorfully printed organic solar cells can be fabricated. Moreover, they are suitable for constructing solar power plants in space, since their light weight allows them to be easily put into orbit. In this section, the history, fundamental principles, and recent progress in organic solar cells are summarized.The most essential factor for organic solar cells is the existence of excitons, that is, strongly bound electron–hole pairs. To efficiently generate photocarriers from excitons, donor–acceptor sensitization is used. Fullerenes acting as acceptors are used in present organic solar cells. Since the diffusion length of excitons is extremely small, blended junctions are used. Route formation both for photogenerated electrons and holes to the respective electrodes by phase separation is required for organic blended junctions. The magnitude of the photovoltage that can be obtained is determined by the difference between the lowest unoccupied molecular orbital (LUMOlowest unoccupied molecular orbital (LUMO)) of the acceptor molecules and the highest occupied molecular orbital (HOMOhighest occupied molecular orbital (HOMO)organic semiconductorfilm) of the donor molecules. Utilization of tandem cells has been effective in increasing the power-conversion efficiency. Today, the power-conversion efficiency of organic solar cells has reached 12%. For the organic semiconductor films used in organic solar cells, both small molecule films deposited by the dry process of vacuum evaporation and polymer films deposited by the wet process of spin coating are used.

Metals reflect, plastics transmit, and water absorbs terahertz-frequency electromagnetic radiation. Such diverse terahertz (THz)frequencyresponses open up a vast range of applications for terahertz materials spanning art, science, engineering, and medicine. The three main components of terahertz devices are sources, detectors, and the intervening optics. Sources include solid-state emitters, typically involving in their operation either the lattice (nonlinear optics) or the charge carriers (transient dipoles). Quantum cascade lasers, built of multiple semiconductor layers, represent a rapidly developing solid-state terahertz source. Detectors typically depend on either the crystal lattice (electro-optical detection) or the charge carrier reservoir (electronic detection) being sensitive to terahertz radiation. Terahertz terahertz (THz)radiationcomponents encompass metal-coated mirrors, plastic (machined, molded, or three-dimensional (3-D) printed) lenses, and waveguides, filters, and polarizers of many different materials and designs. An emerging class of components are the terahertz metamaterialsmetamaterial.

Metamaterials is a new field of interdisciplinary research, which deals with artificial material composites engineered to display physical properties that surpass (or complement) those available in nature. Originally proposed as a way of tailoring media’s electromagnetic and optical properties, the metamaterial concept has recently extended its reach to also include elastic, acoustic, and thermal properties. Since 1999, with the emergence of the field, metamaterials has attracted a lot of attention from the scientific community all over the globe, offering immediate applications in antenna and waveguide engineering, imaging, microscopy, sensing, and light manipulation. Metamaterial research has brought together electrical engineers, material and optical scientists, chemists, and mathematicians; it has also advanced our understanding of electrodynamics, pushed the boundaries of nanofabrication, and stimulated the development of novel characterization techniques. Metamaterial research continues to expand quite rapidly, making it almost impossible to faithfully cover the field even with a reasonably sized book. This chapter attempts to give a brief overview of the history of electromagnetic (photonic) metamaterials, important developments, and main concepts in the field. Also, it aims to provide a basic understanding of the principles, design rules, and tricks routinely exploited by the researchers to achieve the desired material behavior. The chapter is divided into two parts, which are devoted to bulk metamaterials and their two-dimensional counterparts, the so-called planar metamaterials or metasurfaces.

Thermoelectricitythermoelectricity is one of the oldest phenomena to be observed in semiconductors, with discovery of the various thermoelectric effects dating back to the early part of the 19th century. These effects manifest themselves as the appearance of a voltage in a circuit comprised of two different conductors due to a temperature difference (Seebeck effectSeebeck effect), or as the absorption and evolution of heat at the junction of two different materials under electrical current excitation (Peltier effectPeltier effect). These effects can be utilized in devices to generate electrical power from waste heat or to provide solid state cooling, respectively.This chapter reviews the main factors governing thermoelectric effects in solids, and how these factors may be manipulated to produce materials with high thermoelectric figure of merit. The first portion of the chapter covers the main features that determine electrical and thermal transport in crystalline semiconductors, while the latter portion discusses several new approaches to this old problem that hold promise for highly efficient thermoelectric materials in the future.

Transparent conducting oxides (TCOtransparentconducting oxide (TCO)s) such as doped ZnO, In₂O₃ and SnO₂ play important roles as transparent electrodes in commercial applications such as display and lighting devices. Although transparency and electrical conductivity are inherently conflicting, TCOs possess both properties simultaneously. To understand the fundamentals of TCOs, the essetials of the transparency and electrical conductivity are reviewed simply. Comprehension of the essentials enables us to develop novel TCOs following the principles of the materials design that carrier conduction paths should be constructed in wide-gap oxides. Because the electronic structure of oxides is considerably different between the conduction band and the valence band, procedures to form the conduction paths for electrons are in contrast to those for holes. In n-type TCOs, only isotropically spread ns0 orbitals of heavy cations such as Zn2+, In3+ and Sn4+ are necessary to form conduction paths for electrons at the bottom of the conduction band. In p-type TCOs, however, hybridization of orbitals between oxygen 2p6 orbitals and other orbitals such as Cu 3d10, Sn 5s2 and S 3p6 orbitals is essential to shape conduction paths for holes at the top of the valence band.

Crystal structure and important functions of inorganic perovskite oxides are introduced. Perovskite oxides comprise large families among the structures of oxide compounds, and several perovskite-related structures are currently recognized. Typical structures (ABO₃) consist of large-sized 12-coordinated cations at the A-site and small-sized 6-coordinated cations at the B-site. Several complex halides and sulfides and many complex oxides have a perovskite structure. From a variety of compositions and structures, a variety of functions are observed in perovskite oxides. In particular high electronic conductivity, which is at a similar level as metal, and surface activity to oxygen dissociation, are highly attractive in this oxide. Perovskite oxide is now widely used for solid oxide fuel cells.