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semiconductor material
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      During the recent decades, advances in semiconductor materials resulted in the development of a wide range of electronic and optoelectronic devices that affected many aspects of the technological society. From semiconductors to microelectronic and optoelectronic devices (i.e., integrated circuits and devices for the generation and detection of light) for information applications (i.e., computing, memory storage, and communication), these advances and applications were catalyzed by an improved understanding of the interrelationship between different aspects (i.e., structure, properties, synthesis and processing, performance, and characterization of materials) of this multidisciplinary field.
      The main objective of this book is to provide an overview of the basic properties, applications, and major types of semiconductors, as well as characterization methods that are routinely employed in the analysis of semiconductor materials. For details on a wide variety of specific topics, a reader is encouraged to refer to the provided Bibliography section. 
     At this juncture, it would be useful to define a semiconductor. However, without the basic details related to the electronic energy band structure of solids, any definition would be incomplete. Thus, although a more adequate definition and description of semiconductors are given in the following chapters, we can now only say that (i) semiconductors have electrical resistivity in the range between those of typical metals and typical insulators (i.e., between about and (ii) they usually have negative temperature coefficient of resistance, and (iii) the electrical conductivity of semiconductors can be varied (in both sign and magnitude) widely as a function of, e.g., impurity content (e.g., doping), temperature, excess charge carrier injection, and optical excitation. (Note that in all these cases it is implied that charge is carried by electronic particles; this is to differentiate from materials that have high ionic conductivity.) These factors may affect the electrical conductivity of a given semiconductor to vary by several orders of magnitude. Such a capability of varying (or controlling) the electrical conductivity over orders of magnitude in semiconductors offers unique applications of these materials in various electronic devices, such as transistors, and various optoelectronic devices for generation and detection of electromagnetic radiation, including data transmission through fiber-optic networks (i.e., photonics). The present computer
     technology is essentially based on the ability of transistors to act as fast “on” or “off” switches, whereas lightwave communication systems rely on semiconductormaterial-based (i) lasers as the source for photons on the one end and (ii) photodetectors on the other end. An important (and distinctive) property of a semiconductor is its temperature dependence of conductivity, i.e., the fact that the conductivity in semiconductors increases with increasing temperature, whereas the conductivity in metals decreases with increasing temperature. One of the important parameters that often determine the range of applications of a given semiconductor is the fundamental energy band gap, or as it is referred to in the subsequent description, the energy gap, (i.e., the energy separation between the valence and conduction bands), which is typically in the range between 0 and about 4 eV for semiconductors. It should be noted, however, that for semiconductors the boundaries for both the resistivity (between about and and the upper limit of the energy gap (of about 4 eV) are only approximate. For example, some materials (e.g., diamond, having the energy gap of about 5.5 eV) also exhibit semiconducting properties if properly processed (e.g., doped) for applications in semiconductor devices. Some examples of common semiconductors that are widely used in electronic and optoelectronic applications are group IV elemental semiconductors (e.g., Si and Ge), group III–V semiconductor compounds (e.g., AlAs, GaAs, GaP, GaN, InP, InAs, and InSb), group II–VI compounds (e.g., ZnS, ZnSe, ZnTe, CdS, CdSe, and CdTe), and group IV–VI compounds (e.g., PbS, PbSe, and PbTe). In addition to these elemental and binary semiconductors, materials such as ternary (e.g., and and quaternary (e.g., alloys with “tunable” (adjustable) properties are also used in specific device applications. Among these semiconductors, Si is one of the most important materials for electronicdevices (e.g., integrated circuits), since Si-related fabrication technology is most advanced and a nearly defect-free material is readily obtainable. Another important semiconductor for (high-speed) electronic and optoelectronic device applications is GaAs, which has superior electron mobility. A wide variety of semiconductor compounds, mentioned earlier, are commonly used in optoelectronic applications, such as light-emitting devices and radiation detectors. It should be noted that it is the energy gap of a semiconductor that determines the energy (or wavelength) of the emitted or absorbed electromagnetic radiation (in the ultraviolet, visible, or infrared ranges); the availability of a wide variety of semiconductors with appropriate energy gaps makes various semiconductor devices suitable for the detection and emission of electromagnetic radiation in these ranges. In addition, in the ternary and quaternary alloys, the energy gap is tunable by alloying various semiconductors, and that allows the flexibility of producing materials with desired properties by varying the composition (i.e., x and y in the chemical formulas). The topics covered in this book are organized in chapters as follows. Chapter 2 presents a brief description of interatomic bonding, crystal structure, and defects. These concepts are important in understanding semiconductors as threedimensional structures that are composed of assemblies of atoms, which are held together by the interatomic forces and which inevitably contain one or more types
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