Springer Handbook of Electronic and Photonic Materials

This opening chapter will concentrate on the changes in the world of semiconducting materials materialmaterialsemiconductingand devices over the latter half of the twentieth century. Within this field we have chosen to concentrate on a few developments and cannot claim to cover all of the major areas. What we plan to do is give a sense of perspective of how the science and technology of these materials has come to its current state and to present a brief overview of why certain materials are chosen for particular semiconductordevice applicationsdevice applications. We start by identifying some of the earliest developments in our understanding of electronic materials; follow the development of silicon technology silicon technologyfrom the first demonstration of the transistor transistorthrough to todayʼs integrated circuit; track some of the key electronic and optoelectronic uses of the conventional III–V semiconductors; Group III–V semiconductorand end with a review of the last decadeʼs explosion of interest in the III–nitride materials. The band gaps of the semiconductors semiconductorencountered in this chapter are shown in Fig. 1.1 – a figure which will be frequently referred to in explaining the choice of materials for specific applications. Fig. 1.1Parameter perspective: band gaps and lattice parameters of selected semiconductors discussed in the text. The important wavelengths for optical storage (CD, DVD and Blu–Ray) and the 1.55 μm used for efficient data transmission through optical fibres are labelled

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 Matthiessenʼs 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 Nordheimʼs 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 materialʼs refractive refractive 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–Di Dominico. Examples are given of the applicability of the models to actual materials. We present various mechanisms of light light absorption absorption, including absorption by free free 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 to 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 of thin film thin films are outlined. Finally, we present a short technical classification of optical glass glasses and materials.

This work reviews basic concepts from both traditional macroscopic magnetism and unconventional magnetism, in order to understand current and future developments of submicronic spin-based electronics, where the interplay of spin-based electronics electronic and magnetic properties is crucial. Traditional magnetism is based on macroscopic magnetic properties observation and physical quantities are deduced from classical electromagnetism. Physical interpretations are usually made with reference to atomic magnetism, where localized magnetic 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 localised d electronic states). While this picture might be enough to understand some aspects of traditional storage and electromechanics, it is not sufficient when describing condensed matter systems with smaller length scales (progressing toward the nanometer range). In this case, the precise nature of the magnetism (localized, free or itinerant as in Fe, Co and Ni transition metals) should be accounted for, along with the simultaneous presence of charge and spin on carriers. In addition, when we deal with the thin films or multilayers found in conventional electronics, or with objects of reduced dimensionality (such as wires, pillars, dots or grains), the magnetic properties are expected to be different from conventional three-dimensional bulk systems. This chapter is organized as follows. We begin (in the Introduction) by highlighting the new era of submicronic spin-based electronics, and we present a table of papers on the topics we cover in the chapter, for the reader who wishes to learn more. The traditional elements of magnetism, such as the hysteresis loop, conventional types of magnetism and magnetic materials, are then presented (in Sect. 4.1). We then briefly describe (in Sect. 4.2) unconventional magnetism, which can be used to understand new high-tech materials that will be used in future devices based on spintronics and quantum information.

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 down to 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 immensely 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 brevityʼs 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 substance upon illumination. Photoconductivity is especially apparent for semiconductors and insulators, which have low conductivity in the dark. Significant information can be derived on the distribution of electronic states in the material and on carrier generation and recombination processes from the dependence of the photoconductivity on factors such as the exciting photon energy, the intensity of the illumination or the ambient temperature. These results can in turn be used to investigate optical absorption coefficients or concentrations and distributions of defects in the material. Methods involving either steady state currents under constant illumination or transient methods involving pulsed excitation can be used to study the electronic density of states as well as the recombination. The transient time-of-flight technique also allows carrier drift mobilities to be determined.

In this chapter we investigate the 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 the 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 (IFIGS). These intrinsic interface states are the wavefunction 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 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 vs. extrinsic disorder, amorphous vs. crystalline structure, bulk vs. interfacial control, cation vs. anion conduction and ionic vs. 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.

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 (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 IV (Si, Ge, SiGe, diamond, SiC), Group III–V (such as GaAs, InP, nitrides) Group II–IV (including CdTe, ZnSe, MCT) through to a wide range of oxide/halide/phosphate/borate 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. This chapter also does not cover the more fundamental aspects of the growth of the particular materials covered; for these, the reader is again 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 coming ultra-large-scale integration (ULSI) ultra-large-scale integration (ULSI) and system-on-a-chip (SOC) system-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.

The epitaxial growth of thin films of material for a wide range of applications in electronics and optoelectronics is a critical activity in many industries. The original growth technique used, in most instances, was liquid-phase liquid-phase epitaxy (LPE) epitaxy (LPE), as this was the simplest and often the cheapest route to producing device-quality layers. These days, while some production processes are still based on LPE, most research into and (increasingly) much of the production of electronic and optoelectronic devices now centers on metalorganic chemical vapor deposition (MOCVD) metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) molecular beam epitaxy (MBE). These techniques are more versatile than LPE (although the equipment is more expensive), and they can readily produce multilayer structures with atomic-layer control, which has become more and more important in the type of nanoscale engineering used 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. Some examples of growth in various important systems are also outlined for each of the three techniques.

The field of narrow-bandgap Group II–VI semiconductor II–VI semiconductors is dominated by the compound Hg_1−x Cd _x Te (CMT), although some Hg-based alternatives to this ternary have been suggested. The fact that CMT is still the preeminent infrared (IR) infrared (IR) material stems, in part, from the fact that the material can be made to cover all IR regions of interest by varying the x value. In addition, the direct band transitions in this material result in large 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 reported for infrared detectors of comparable wavelengths. This chapter covers the growth of CMT 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 metalorganic vapor phase and molecular beam epitaxies (used mainly for third-generation infrared detectors, including two-color and hyperspectral detectors). Growth on silicon substrates is also discussed.

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 (LPE), vapor-phase epitaxy (VPE) containing conventional VPE, hot-wall epitaxy (HWE), metalorganic chemical vapor deposition (MOCVD) or metalorganic phase epitaxy (MOVPE), molecular-beam epitaxy (MBE) and atomic-layer epitaxy (ALE). In bulk crystal growth, two typical growth methods, chemical/physical vapor transport (CVT/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 of surface chemical analysis surface chemical analysis techniques are described in the context of semiconductor semiconductoranalysis analysis. Particular emphasis is placed on the SIMS (secondary ion mass spectrometry) technique, as this is one of the more useful tools for routine semiconductorcharacterization 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 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 theory Debye theoryof the heat capacity, which has been widely used for many decades for calculating the C_P of crystals. The thermal properties are interrelated through Grüneisenʼs theorem. Various useful empirical rules for calculating C_P and κ have been used, some of which are summarized. Conventional differential scanning differential scanning calorimeter (DSC)calorimetry (DSC) is a powerful and convenient thermal analysis thermal analysistechnique that allows various important physical and chemical transformations, such as the glass transition, glass transitiontemperaturecrystallization, 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 solid-state physics (e.g. [21.1,2]), semiconductor physics (e.g. [21.3]), semiconductor optics (e.g. [21.4]) and electronic devices (e.g. [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 (MOS) transistors for advanced complementary 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.

The history of gallium arsenide is complicated because the technology required to produce GaAs gallium arsenide (GaAs) devices has been fraught with problems associated with the material itself and with difficulties in its fabrication. Thus, for many years, GaAs was labelled as “the semiconductor of the future, and it will always be that way.” Recently, however, advances in compact-disc (CD) technology, fibre-optic communications and mobile telephony have boosted investment in GaAs research and development. Consequently, there have been advances in materials and fabrication technology and, fabricationtechnology as a result, GaAs devices now enjoy stable niche markets. gallium arsenide (GaAs)device The specialised uses for GaAs in high-frequency and optoelectronic applications result from the physical processes of electron motion that allow high-speed and efficient light emission to take place. In this review, these advanced devices are shown to result from the physical properties of GaAs as a semiconducting material, the controlled growth of GaAs and its alloys and the semiconductionmaterial subsequent fabrication into devices. Extensive use is made of chapters from “Properties of Gallium Arsenide, 3rd edition” which I edited with the help of Prof. G. E. Stillman [23.1]. This book was written to reflect virtually all aspects of GaAs and its devices within a readable text. I believe that we succeeded in that aim and I make no apologies in referring to it. Readers who need specialised data, but not necessarily within an explanatory text, should refer to the Landolt-Börnstein, group III (condensed matter) data collection [23.2,3]. The sub-volumes A1α (lattice properties) and A2α (impurities and defects) within volume 41 are rich sources of data for all III–V compounds. Although there are no better sources than the original research papers, I have referred to textbooks where possible. This is because the presentation and discussion of scientific data is often clearer than in the original text, and these books are more accessible to students. Gallium arsenide (GaAs) is one of the most useful of the III–V semiconductors. In this Group III–V semiconductor chapter, the properties of GaAs are described and the ways in which these are exploited in devices are explained. The limitations of this material are presented in terms of both its physical and its electronic properties.

The physical and chemical properties of wide-band-gap semiconductors make these materials an ideal wide bandgapsemiconductor choice for device fabrication for applications in many different areas, e.g. light emitters, high-temperature and high-power electronics, high-power microwave devices, micro-electromechanical system (MEM) technology, and substrates for semiconductor preparation. These semiconductors have micro-electromechanical system (MEMS) been recognized for several decades as being suitable for these applications, but until recently the low material quality has not allowed the fabrication of high-quality devices. In this material quality chapter, we review the wide-band-gap semiconductors, silicon carbide and diamond. Silicon carbide electronics is advancing from the research stage to commercial production. The commercial availability of single-crystal SiC substrates during the early 1990s gave rise to intense activity in the development of silicon carbide devices. The commercialization started with the release of blue light-emitting diode (LED). The recent release of high-power Schottky diodes was a further demonstration of the progress made towards defect-free SiC substrates. Diamond has superior physical and chemical properties. Silicon-carbide- and diamond-based diamondsilicon carbide (SiC) electronics are at different stages of development. The preparation of high-quality single-crystal substrates of wafer size has allowed recent significant progress in the fabrication of several types of devices, and the development has reached many important milestones. However, high-temperature studies are still scarce, and diamond-based electronics is still in its infancy.

This chapter is devoted to a survey of the structural, optical optical properties and electrical properties electrical properties of amorphous semiconductors amorphous 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 semiconductors, amorphous semiconductor i.e., a-Si:H and related materials, and chalcogenide glasses 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-silicon solar 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 transistors and their electrical isolation, as well as passive devices, such as capacitors. 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 interconnect 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. Portions of the survey presented here are selected from work previously published by the author [28.1,2,3].

This chapter provides an extended introduction to the basic principles of thin-film technology, thin 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 methods deposition 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 films thin 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 the morphological characteristicsclassification 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 semiconductionthin film 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 film thick 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 the thick film fabrication 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 hybrid microelectronic circuits 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 parameters; (2) Mechanical, elastic, and lattice vibronic properties; (3) Thermal properties; (4) Energy band parameters; (5) Optical properties, and; (6) 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 and mechanical properties of group III nitrides, including of AlN, GaN, InN and their ternary and quaternary compounds are discussed. The driving force for semiconductor nitrides is device applications for emitters and detectors in the visible and ultraviolet (UV) portions of the optical spectrum and high-power amplifiers. Further advances in electronic and optoelectronic devices, which are imperative, require better understanding and precise measurements of the mechanical, thermal, electrical and optical properties of nitride semiconductors. Information available in the literature regarding many of the physical properties of nitrides, especially AlN and InN, is still in the process of evolution, and naturally in the subject of some controversy. This is, in part, a consequence of measurements having been performed on samples of widely varying quality. When possible, these spurious discrepancies have been disregarded. For other materials, too few measurements are available to yield a consensus, in which case the available data are simply reported. The aim of this work is to present the latest available data obtained by various experimental observations and theoretical calculations.

The III–V nitride semiconductor semiconductors, gallium nitride, aluminium 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 underlying electronic material electronic materials, the electron transport that occurs within these III–V nitridesemiconductor 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 current literature. In order to narrow the scope of this chapter, we will primarily focus on electron transport within bulk wurtzite gallium nitride, aluminium nitride, and indium nitride for this analysis. Most of our discussion will focus on results obtained from our ensemble semi-classical three-valley Monte Carlo simulations Monte Carlo simulations of the electron 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 present Chapter deals with the wide-band-gap (defined here as greater than 2 eV) Zn chalcogenides, i.e. ZnSe, ZnS, and ZnO (mainly in bulk form). However, since recent literature on ZnS is minimal, the main coverage is of ZnSe and ZnO. In addition Zn_1−x Be _x Se (x ≤0.5) is included, since Be is expected to reduce degradation (from light irradiation/emission) in ZnSe. The main emphasis for all these materials is on doping, in particular p-type doping, which has been a problem in all cases. In addition, the origin of light emission in ZnO is not yet well established, so this aspect is also briefly covered.

The field of narrow-gap II–VI materials is dominated by the compound semiconductor mercury cadmium telluride, (Hg_1–x Cd _x Te or MCT), which supports a large industry in infrared detectors, detectorinfraredcameras and infrared systems. It is probably true to say that HgCdTe is the third most studied semiconductor after silicon and gallium arsenide. Hg_1–x Cd _x Te is the material most widely used in high-performance infrared detectors at present. By changing the composition x the spectral response of the detector can be made to cover the range from 1 μm to beyond 17 μm. The advantages of this system arise from a number of features, notably: close lattice matching, high optical absorption coefficient, low carrier generation rate, high electron mobility and readily available doping techniques. These advantages mean that very sensitive infrared detectors can be produced at relatively high operating temperatures. Hg_1–x Cd _x Te multilayers can be readily grown in vapor-phase epitaxial processes. This provides the device engineer with complex doping and composition profiles that can be used to further enhance the electro-optic performance, leading to low-cost, large-area detectors in the future. The main purpose of this chapter is to describe the applications, device physics and technology of II–VI narrow-bandgap devices, focusing on HgCdTe but also including Hg_1–x Mn _x Te and Hg_1–x Zn _x Te. It concludes with a review of the research and development programs into third-generation infrared detector technology detectortechnology(so-called GEN III detectors) being performed in centers around the world.

Unlike 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-fibre 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 the most important optoelectronic devices. The influence of carrier–photon interactions is discussed in the context of producing efficient 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 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 crystals liquid crystal 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 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. electrophotographyIncluded in the discussion are the materials (polymers, pigments, charge-transport molecules, etc.), device architecture, photoreceptordevice architecturefabrication methods, and device electrical characteristics photoreceptororganicphotoreceptorelectrical characteristicthat 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 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 stimulated luminescencephosphortelevision screensX-ray storage current applications, including plasma television screens, long-term persistent phosphors, X-ray storage phosphors, scintillators, and phosphors for white LEDs.

Photonic nanoengineeringcrystals offer a well-recognized ability to control the propagation of modes of light in an analogous fashion to the way in which nanostructures nanostructurehave 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 photonic device with applications in areas including communications, computing and sensing, for example. In such applications, photonic crystals photonic crystal (PC)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 to the near-infrared (≈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, telecommunicationwhere it offers mechanisms for selective switching, for example. This review discusses alternative proposals for tuning of such photonic crystals.

This quantum well (QW)superlattice (SL)band gapengineeringchapter reviews the principles of band-gap engineering and quantum confinement quantum confinement in semiconductors, with a particular emphasis on their optoelectronic properties. The chapter begins with a review of the fundamental principles of band-gap engineering and quantum confinement. It then describes the optical and electronic properties of semiconductor quantum wells semiconductorquantum well and superlattices at a tutorial level, before describing the principal optoelectronic devices. The topics covered include edge-emitting lasers edge-emitting laser and light-emitting diodes light emitting diode (LED) (LEDs), resonant cavity LEDs and vertical-cavity surface-emitting lasers (VCSELs), vertical-cavity surface-emitting laser (VCSEL) quantum cascade lasers, quantum cascade laser (QCL) quantum-well solar cells, superlattice avalanche photodiodes, inter-sub-band detectors, and quantum-well light modulators. The chapter concludes with a brief review of current research topics, including a discussion of quantum-dot structures.

Inorganic glasses are the workhorse materials of optics and photonics. In addition to offering a range of transparency windows, glasses provide flexibility of processing for the realization of fibers, films, and shaped optical elements. Traditionally, the main role of glass has been as a passive material. However, a significant attribute of glasses is their ability to incorporate dopants such as nanoparticles or active ions. Hence, glasses promise to play an increasingly important role in active photonics, as laser, amplification, switching, and nonlinear 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 viscosity of a glass during processing can be exploited in the 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 implemention of 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 are also introduced. Prominent resonant-type nonlinearity in particle-embedded glasses is described. For second-order nonlinearity, a variety of poling methods are summarized. Finally, it is pointed out that various photoinduced changes can appear when excited by linear and nonlinear optical processes, and this is related to glass structure.

In a nonlinear optical material, intense light alters the real and imaginary components of the refractive index. The nonlinear response of the real part of refractive index modifies the phase of propagating light, while the imaginary part describes the change in absorption. These illumination-dependent properties of nonlinear materials provide the basis for all-optical switching—the ability to manipulate optical signals without the need for optical–electronic–optical conversion. In this chapter we review the physical processes underlying the illumination-dependent refractive index. We review the real and imaginary nonlinear response of representative groups of materials: crystalline semiconductors, organic materials, and nanostructures, and we examine the practical applicability of these groups of materials to all-optical optical switching. We identify the spectral regions which offer the most favorable nonlinear response as characterized using engineering figures of merit.

Photovoltaic solar cells solar cellphotovoltaic 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 cells photovoltaic solar cellsolar cell photovoltaic and the challenge of extracting the maximum amount of electrical energy electrical energy from the available solar energy. 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 five very different materials systems, from crystalline silicon crystalline silicon through to polycrystalline thin films. polycrystallinethin films These materials have been chosen because they are all in production, although some are only in the early stages of production. Many more materials are being considered in research and some of the more exciting, polymer and dye-sensitised cells are mentioned in the conclusions. 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 filmsemiconductor thin-film semiconductors and dielectrics are critical requirements for large-area electronics, including displays and imagers. Despite the presence of structural disorder, these materials show promising electronic transport properties that are vital for devices such as thin filmtransistor (TFT) thin-film transistors (TFTs). This chapter presents an overview of material and transport properties pertinent to large area electronic large-area electronics on mechanically flexible substrate 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 amorphoussemiconducting film amorphous semiconducting films, along with their influence on TFT characteristics. The TFTs must maintain electrical integrity under mechanical stress, induced by bending of the flexible substrates. Bending-induced changes are not limited to alteration of device dimensions and involve modulation of electronic transport of the active semiconducting layer.

Recent flat-panel X-ray imaging detectors have been shown to be able to replace present-day X-ray film/screen cassettes; 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 detectorimaging 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, quantum efficiencyresolution in terms of the modulation transfer function, modulation transfer function (MTF)image lagimage lag and ghosting; and examines how these metrics depend on the photoconductor, and detector structure and design.

The present chapter takes the reader from the basics of phase-change recording recording up to the latest achievements in the field. It discusses in detail the specific features of Te-based compounds that made them the best materials for phase-change data storage. phase-change data storage It is demonstrated that the essence of phase-change recording does not consist of simple disordering of the medium through melting and subsequent quenching as previously believed but is due to a switch of Ge atoms between octahedral and tetrahedral symmetry positions within the Te face-centered cubic lattice. It is this nature of the transition that makes the Te-based media fast and stable. The chapter is concluded by the introduction of a concept of the super-resolution near-field structure (super-RENS) super-resolution near-field structure (super-RENS) disc that allows the reduction of the bit size well below the diffraction limit diffractionlimit and makes 100 GB/disc storage a reality.

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.

The purpose of this chapter to review the current status of magnetic materials used in data storage. The emphasis is on magnetic materials magnetic materialmaterialmagneticused in disk drives disk drivesand in the emerging technology of the magnetic random-access memory (MRAM). A wide range of magnetic materials is essential for the advance of magnetic recording both for magnetic recording heads and media, including high-magnetization soft-magnetic materials for write heads, new antiferromagnetic alloys alloyswith high blocking temperatures and low susceptibility to corrosion for pinning films in giant-magnetoresistive (GMR) sensors sensorand new ferromagnetic alloys with large values of giant magnetoresistance. For magnetic recording media, the advances are in high-magnetization metal alloys with large values of the switching coercivity. A significant limitation to magnetic recording is found to be the superparamagnetic effect and new advances 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 be the dominant recording technology in the future. The MRAM device uses some of the same materials as used in the GMR sensor, but the key technology is the magnetic tunneling junction in which soft-magnetic films magnetic filmare coupled by a thin insulating film and conduction is by quantum-mechanical tunneling. The status of the MRAM technology MRAM technologyand some of the 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 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 superconductorsuperconductorhigh-temperature high-temperature superconductors and their physical properties is presented. Starting from the well-known characteristics of conventional superconductors, described in Sect. 52.1, the new phenomena observed in high-temperature superconductors are considered. The complexity of the physical properties of the cuprate superconductor cuprate superconductors is closely related to the fact that these materials are close to a metal–insulator metal–insulator transition transition. In Sects. 52.2 and 52.3 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. 52.4. The binary compound MgB₂ is strictly speaking not a high-temperature superconductor. Nevertheless, an overview of the physical properties of this interesting metallic superconductor metallic superconductor, characterised by a transition transition temperature temperature as high as 39 K, has been included in the present chapter (Sect. 52.5).

The prospects of using organic materials organic material in electronics electronics and optoelectronics applications have attracted scientists and technologists since the 1970s. This field has become known as molecular electronics. molecular electronics Some successes have already been achieved, for example the liquid-crystal display. Other products such as organic light-emitting displays, organic light emitting display chemical sensors chemical sensor and plastic transistors plastic transistor 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 organic materialfor chemical sensing are broadly classified into three categories: (i) macrocyclic compounds, macrocylic compound(ii) conducting polymers conducting polymerpolymerconductingand (iii) cavitand molecules. cavitand compundA short review of current progress in semiconductor oxide sensing semiconductoroxide sensingsensingmaterialmaterials is given, pointing out their strengths and limitations. Principal wet techniques for depositing organic thin films thin filmorganicare described and electrical, optical and structural properties of all three types of organic materials are analysed 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 dielectric or insulators insulatorand polymers used as insulators and, in a composite form, as conductors. conductorThere is a need for new materials to meet the ever-changing requirements for high-speed digital and radio-frequency (RF) applications. There are different requirements for digital and RF packages that translate into the need for unique materials for each application. The interconnect and dielectric (insulating) requirements are presented for each application and the relevant materials properties and characteristics are discussed. The fundamental materials characteristics are: dielectric constant, dielectric loss, thermal and electric conductivity, resistivity, moisture absorption, glass-transition temperature, strength, time-dependent deformation (creep), and fracture toughness. The materials characteristics and properties are dependant on how they are processed to form the electronic package electronic packagingmaterialso the fundamentals of electronic packaging processes are discussed including wirebonding, solder interconnects, flip-chip interconnects, underfill for flip chip and overmolding. The relevant materials properties are given along with requirements (including environmentally friendly Pb-free packages) that require new materials to be developed to meet future electronics electronic materialneeds for both digital and RF applications.