Technology & Engineering
Semiconductors
Semiconductors are materials with electrical conductivity between that of a conductor and an insulator. They are the foundation of modern electronics, serving as the basis for transistors, diodes, and integrated circuits. By controlling the flow of electrical current, semiconductors enable the functionality of electronic devices such as computers, smartphones, and solar cells.
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11 Key excerpts on "Semiconductors"
eBook - PDFNavigating the Materials World
A Guide to Understanding Materials Behavior
- Caroline Baillie, Linda Vanasupa(Authors)
- 2003(Publication Date)
- Academic Press(Publisher)
CHAPTER 9 An Electronic Trip Through Semiconductors E mily A llen and S usan A. A mbrose 0-12-073551-2 Copyright 2003, Elsevier Science (USA). All rights reserved. 195 Welcome Welcome to the land of Semiconductors . Until now, you’ve probably been traveling to places that were somewhat familiar to you, full of materials that you encounter in your everyday life. Metals and ceramics, for example, have been explored by humans for millennia. However, now you’re in a world of materials whose properties weren’t even known until late in the 20th century.To attain a deep understanding of semiconductor materials, you’ll probably need to visit the worlds of quantum mechanics and electrical engineering; those destinations might be later in your journey. On your visit here, though, we’ll show you the useful properties of semiconductor materials, and why they are so valuable to our modern world. Because you’re living in the 21st century, you know that semiconduc-tor materials are used all around you in advanced technology. Computers and communication equipment, sensors, transportation, automation, and entertainment devices all have at their hearts one or more semiconductor chips to provide functional control and data storage.These chips are actu-ally composed of small pieces of semiconductor material with electronic circuits embedded in them. The unique properties of Semiconductors allow us to make versatile components of electronic circuits, such as resis-tors, capacitors, diodes, and transistors, all on the same small piece of mate-rial. We won’t discuss those circuits here, or even the component devices that make up the circuits. Instead, we’ll focus only on the properties and behaviors of the semiconductor materials.Table 9.1 shows some common applications of semiconductor materials. Like all materials, the crystallographic and defect structure of the semi-conductor material determines its structural, mechanical, electrical, ther-modynamic, and other properties.
- Wei Gao, Nigel M Sammes;;;(Authors)
- 1999(Publication Date)
- WSPC(Publisher)
Five Semiconductor Properties and Materials 5.1. Introduction 5.1.1. Introduction and Brief History Semiconductors form the basis of the electronics industry. They have had a major impact on the development of the modern technological society in which we live in. Without semiconductor technology, we would not have modern electronic devices, instruments and equipment, including stereos, TVs, VCRs, automatic cameras, mobile phones, computers and telecom-munication systems. Research in the semiconductor field began in the middle of the 19th century. M. Faraday reported the first recorded observation in 1833 and showed that silver sulphide has a negative TCR. However, the research progress was very slow during those early years. During the interval be-tween the two World Wars, military and commercial applications such as radios, radar, power rectifiers, infra-red detectors and photoelectric devices developed rapidly. In 1947, the transistor was developed at Bell Labs USA, which later led to an extensive investigation in solid-state electronics called the solid integrated circuit (IC). Today, the largest ULSI (Ultra Large-Scale Integrated Circuits) contain > 10 7 components per chip. The modern 63 64 An Introduction to Electronic and Ionic Materials PC computer Pentium® 133 uses Intel's advanced 0.35 fim technology, re-sulting in a chip the size of a small child's fingernail, but containing 3.3 million transistors. The small chip size makes it possible for systems to deliver a high level of performance with very low power consumption, and makes them especially suitable for notebook-type computers. Since the 1980s, the semiconductor industry has become one of the largest industries in the world. 5.1.2. Energy Band Structure in Metals, Insulators and Semiconductors As described in Chapter 3, the electrons in a solid are constrained to have energies which lie in a number of energy bands. The band structure deter-mines the electrical properties of these materials (Fig. 5.1).
eBook - PDF- Michael R Fisch(Author)
- 2004(Publication Date)
- WSPC(Publisher)
Chapter 1 1 Semiconductors 11.1 Overview Almost all common electronic devices use Semiconductors. Yet, many read- ers might not be able to answer the question, “What is a semiconductor?” Similarly, they might not know the most basic science and technology of this important class of materials. In the spirit of trying to build understanding from the basics, this chapter introduces the reader to Semiconductors. The basic question, “What is a semiconductor?” will be addressed first. In practice, pure Semiconductors are not as technologically useful as “doped Semiconductors,” Semiconductors containing controlled amounts of impuri- ties. Thus, we will ask: (1) What is a semiconductor? (2) What is a doped semiconductor? (3) How are Semiconductors doped? (4) Why are Semiconductors doped? (5) How are Semiconductors used to make electronic devices? (6) What are some electronic devices? (7) How do semiconductor devices work? 11.2 Introduction Semiconductors are of great importance to our everyday life. Almost every appliance, electronic entertainment device, and automobile contains semi- conductors, in the form of transistors, that are part of integrated circuits that are part of more complex systems. While the details of semiconductor technology are very complex, a basic understanding of what semiconduc- 189 190 LIQUID CRYSTALS, LAPTOPS AND LIFE tors are and how they are used is not too complex and is vitally important to our later understanding of the computer. The macroscopic behavior of Semiconductors may be distinguished from metals and insulators in two ways. First, as the name implies, the (elec- trical) conductivity, or ability to conduct electricity, at room temperature is between that of metals (much higher electrical conductivity) and insula- tors (much lower conductivity). It is important to realize that this range of conductivity is quite large.
eBook - PDFMaterials Engineering
Proceedings of the First International Symposium, University of the Witwatersrand, Johannesburg, South Africa, November 1985
- J. V. Bee, G. G. Garrett, D M R Taplin, J. V. Bee, G. G. Garrett, D M R Taplin(Authors)
- 2013(Publication Date)
- Pergamon(Publisher)
It was this fundamental work on Ge which made possible the invention of the first transistor in 1947 (Pearson and Brattain, 1955). Semiconductors TODAY With the advent of the transistor in 1947 and PbS infrared detectors during the Second World War, (Smith, 1953) the field of semiconductor technology received a major impetus. Entire ranges of new Semiconductors have been developed and the diversity of applications has mushroomed. To lay the foundation for the rest of this paper we briefly review those parameters associated with Semiconductors which are generally adequate to appreciate the differences between the different materials. What is a semiconductor? The model for semiconductor behaviour is based on the energy band theory of solids. The generalized semiconductor is taken to have its valence band completely filled at 0 K and its conduction band completely empty, the two bands being separated by an amount of energy greater than zero known as the energy gap. As the temperature is increased above 0 K, electrons are statistically excited from the valence band to the conduction band, the den-sity of charge carriers thereby increasing exponentially with temperature as opposed to metals where the density of charge carriers remains essentially constant. The greater the bandgap, the greater the temperature required to significantly increase the free electron density. An insulator behaves in a similar fashion but its energy gap is very large. Both the conduction and valence bands are taken to be essentially parabolic in shape, leading to the definition of an effective mass for free electrons in the conduction band m e . The electrons excited to the conduction band leave behind them holes in the valence band which may be viewed as positively charged free particles with an effective mass m n . For a pure or so-called intrinsic semiconductor the density of free electrons n and free holes p is the same.
eBook - PDF- Fumio Shimura(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
Chapter 4 Basic Semiconductor Physics Although this b o o k aims to provide comprehensive a n d up-to-date k n o w l -edge of the semiconductor silicon crystal technology, the ultimate objective of this effort is not only to contribute to the p r o d u c t i o n of state-of-the-art V L S I / U L S I devices but also to create future electronic devices on the basis of silicon materials. T o this end, u n d e r s t a n d i n g semiconductor physics is unquestionably helpful to the further use of silicon materials. In this chapter, the basic semiconductor physics considered to be essential to develop an understanding of semiconductor crystals is described. T h e subjects emphasized in this chapter include (1) electrical conductivity a n d (2) basic electronic-device operation physics. F o r detailed consideration of Semiconductors a n d their device physics, the reader should consult the s t a n d a r d text b o o k s such as Refs. 1-5 listed at the end of this chapter. 4.1 Semiconductors 4.1.1 Properties of Semiconductors Definition of Semiconductor W h a t is a semiconductor? W h a t are its proper-ties? Although the term s e m i c o n d u c t o r is well k n o w n , it m a y n o t be easy to answer these questions quickly. A semiconductor is often defined simply from the viewpoint of electrical conductivity cr. T h a t is, Semiconductors are materials with values of the electrical resistivity p (= 1/a) at r o o m tempera-ture generally in the range of ~ 1 0 ~ 2 to 1 0 9 Q c m , intermediate between conductors ( ~ 1 0 ~ 6 Q cm) a n d insulators ( ~ 1 0 4 to ~ 1 0 22 Q cm). Indeed, the term s e m i c o n d u c t o r is from such an electrical conductive characteristic. Electrical Properties A semiconductor has been defined as a material that has intermediate conductivity. However, a pure a n d perfect crystal of m o s t 82
- Rolf Enderlein, Norman J Horing(Authors)
- 1997(Publication Date)
- World Scientific(Publisher)
With the introduction of silicon, the stage was set for the development of semiconduc- tor microelectronics. Later, a similar role was played by compounds involv- ing elements of the third and fifth groups of the periodic table, like gallium 1.2. Atornic structure of ideal mystah 5 arsenide or phosphide, making possible the development of semiconductor optoelectronirs. The broad technical application of its results distinguishes semiconduc- tor physics now from its early days. It is well established that semicondnc- tors arc exceptionally well-suited for necessary functions in electronics and electrical engineering. This is by no means accidental, but is due to the mi- croscopic nature of Semiconductors, which permits the controlled variation of characteristic matprial properties by external means over a wide range of parameters. The great technical importance of Semiconductors has made thorough physical investigation of these materials necessary, but it has also justified the high cost involved in their fabrication and study. Owing to both of these aspects Semiconductors are thc best explored and understood materials of condensrd matter today. Moreover, a multitude of physical phe- nomena which occur in other solid state materials may also be observed in Semiconductors, often in the most distinctive way. For this reason studies of Semiconductors can also provide knowledge of other solid state mattri- als. Semiconductors have in fact become model systems for basic research in condensed matter physics. The presentation of the microscopic principles of semiconductor physics will occupy most of this book. The introductory first chapter lies outside of this framework because it involves discussion of the results on a phe- nomenological basis. The characterization of Semiconductors by means of their unique macroscopic features, which we have touched upon above, will be continued in Chapter 1.
eBook - PDFPrinciples of Transistor Circuits
Introduction to the Design of Amplifiers, Receivers and Digital Circuits
- S W Amos, Mike James(Authors)
- 2013(Publication Date)
- Newnes(Publisher)
The principles described apply to circuits employing discrete transistors and those embodied in i.c.s. To explain the properties of transistors it is useful to begin with an account of the physics of 1 2 Principles of Transistor Circuits Semiconductors because all transistors, irrespective of type, depend on semiconducting material for their action. MECHANISM OF SEMICONDUCTION As the name suggests a semiconducting material is one with a conductivity lying between that of an insulator and that of a conductor: that is to say one for which the resistivity lies between, say 10 1 2 Q-cm (a value typical of glass) and 10~ 6 Ω-αη (approximately the value for copper). Typical values for the resistivity of a semiconduct-ing material lie between 1 and 100 Ω-cm. Such a value of resistivity could, of course, be obtained by mixing a conductor and an insulator in suitable proportions but the resulting material would not be a semiconductor. Another essential feature of a semiconducting material is that its electrical resistance TEMPERATURE Fig. 1.1. Resistance-temperature relationship for a conductor and a semiconductor decreases with increase in temperature over a particular tem-perature range which is characteristic of the semiconductor. This behaviour contrasts with that of elemental metallic conductors for which the resistance increases with rise in temperature. This is illustrated in Fig. 1.1, which gives curves for a conductor and a semiconductor. The resistance of the conductor increases linearly, whereas that of the semiconductor decreases exponentially, as temperature rises. Over the significant temperature range the relationship between resistance and temperature for a semiconductor could be written R ( = ae h T where R, is the resistance at an absolute temperature 7 a and b are constants characteristic of the semiconductor material and e is the Semiconductors and Junction Diodes 3 base of the natural logarithms, i.e.
eBook - PDFPrinciples of Transistor Circuits
Introduction to the Design of Amplifiers, Receivers and Digital Circuits
- S W Amos(Author)
- 2013(Publication Date)
- Butterworth-Heinemann(Publisher)
The principles described apply to circuits employing discrete transistors and those embodied in i.c.s. To explain the properties of transistors it is useful to begin with an account of the physics of 1 2 Principles of Transistor Circuits Semiconductors because all transistors, irrespective of type, depend on semiconducting material for their action. MECHANISM OF SEMICONDUCTION As the name suggests a semiconducting material is one with a conductivity lying between that of an insulator and that of a conductor: that is to say one for which the resistivity lies between, say 10 12 Ω-αη (a value typical of glass) and 10~ 6 Q-cm (approximately the value for copper). Typical values for the resistivity of a semiconduct-ing material lie between 1 and ΙΟΟΩ-cm. Such a value of resistivity could, of course, be obtained by mixing a conductor and an insulator in suitable proportions but the resulting material would not be a semiconductor. Another essential feature of a semiconducting material is that its electrical resistance i Ul o z < UJ TEMPERATURE ► Fig. 1.1. Resistance-temperature relationship for a conductor and a semiconductor decreases with increase in temperature over a particular tem-perature range which is characteristic of the semiconductor. This behaviour contrasts with that of elemental metallic conductors for which the resistance increases with rise in temperature. This is illustrated in Fig. 1.1, which gives curves for a conductor and a semiconductor. The resistance of the conductor increases linearly, whereas that of the semiconductor decreases exponentially, as temperature rises. Over the significant temperature range the relationship between resistance and temperature for a semiconductor could be written R t = ae blT where R t is the resistance at an absolute temperature T, a and b are constants characteristic of the semiconductor material and e is the Semiconductors and Junction Diodes 3 base of the natural logarithms, i.e.
eBook - PDF- Ron Graham(Author)
- 2005(Publication Date)
- Whittles Publishing(Publisher)
In between these two types of material we have the Semiconductors. 4.2 Semiconductors Those elements with four electrons in the valence bands of their atoms, and com- pounds made up of one element with three valence electrons and another with five valence electrons, may be Semiconductors. Semiconductors are used to make solid-state electronic components, and some of these are light-sensitive devices that employ the photoelectric effect. One such photo- cell is the cadmium sulphide (CdS) photoresistor, which has a resistance that can vary from millions of ohms in total darkness to a few tens of ohms when illuminated. Another device is the metal oxide semiconductor (MOS) employed in CCDs. Semiconductors have an energy band diagram similar to that of an insulator, but the gap between the valence and conduction bands is very narrow, as shown in Fig. 4.1(b). At absolute zero (zero degrees Kelvin) a pure semiconductor is an insulator, Fig. 4.1 Typical energy bands for (a) an insulator, and (b) a semiconductor but at room temperature (about 20 °C, or 290 K) the mean thermal energy of an elec- tron follows the expression: E t = 3kT/2 (4.3) where: E t is the mean energy of translation of a molecule, k is Boltzmann’s constant, 1.38 10 –23 JK –1 (joules per Kelvin), T is the absolute temperature of the molecule (in degrees Kelvin). If we take a value for T as 290 K, and since 1 eV = 1.6 10 –19 joules we can calcu- late the mean thermal energy of an electron at room temperature to be in the region of 0.04 eV. However, some of the valence electrons will have much more thermal energy than this, and can easily overcome the 0.75 eV forbidden energy gap of a ger- manium semiconductor, or the 1.1 eV forbidden gap of a silicon semiconductor. Semiconductors are often ‘doped’ with controlled amounts of impurities so that the dopant lowers the resistance of the semiconductor to allow more current to flow through the device.
eBook - PDF- Md Nazoor Khan, Simanchala Panigrahi(Authors)
- 2017(Publication Date)
- Cambridge University Press(Publisher)
12 Semiconductors 12.1 Introduction No property of solids varies as widely as their ability to conduct electric current. Copper, a good conductor, has a resistivity of 1.7 × 10 –8 W m at room temperature, whereas quartz, a good insulator, has a resistivity of 7.5 × 10 17 W m, more than 25 powers of ten greater. Thus, based on the ability of solids to carry electric currents, solids are classified into three categories: i. Conductors ii. Insulators iii. Semiconductors Materials which conduct electric current when a small potential difference is applied across them are known as good conductors. At room temperatures the resistivity of a good conductor is of the order of 10 –8 W m. The valence band in conductors is completely filled, while the conduction band is partially filled. Therefore, when a small potential difference is applied to a conductor, it provides sufficient energy to the electrons in the valence band to jump to the conduction band where they result in currents in the conductor. The energy band diagrams of conductors have been discussed in chapter 11. Materials which do not conduct electric current under ordinary potential difference under normal conditions are known as insulators. At room temperature, the resistivity of an insulator is of the order of 10 17 W m . In case of insulators, the valence band is completely filled, the conduction band is completely empty and the forbidden energy band is very large. In case of diamond, a good insulator, the forbidden energy gap is ª 7 eV and an enormous electric field of 10 8 V/m is required to make it conduct current. The energy band diagrams of insulators have already been discussed in chapter 11. 430 Principles of Engineering Physics 2 12.2 Semiconductors Generally, the term semiconductor is applied to a class of materials having conductivity in between a conductor and an insulator. The forbidden energy band in Semiconductors lies roughly in between 0.2 eV to 2.5 eV.
- Dale R. Patrick, Stephen W. Fardo(Authors)
- 2020(Publication Date)
- River Publishers(Publisher)
Chapter 3 Semiconductor Devices INTRODUCTION Nearly any study of semiconductor devices begins with an investigation of atomic theory. This is purposely done to familiarize the reader with a number of ideas re- lated to semiconductor operation. Chapter 1 examined electrons, protons, and neutrons. Each of these parts had a specific role in the construction of an atom. Elements are classified according to the number of particles they possess. No two elements have the same physical struc- ture. OBJECTIVES Upon completion of this chapter, you will be able to: 1. Explain how semiconductor devices functionally operate. 2. Distinguish between conductors, Semiconductors, and insulators. 3. Describe the crystal structure of representative semiconductor diodes and amplifying devices. 4. Describe the operation of devices in a circuit. 5. Be familiar with semiconductor device packaging and symbol representations. 6. Recognize the functional operation of diodes and amplifying semiconductor devices. 7. Describe how to test semiconductor devices and evaluate their status. 8. Describe forward and reverse bias characteristics of diodes. 9. Explain voltage-current characteristics of semicon- ductor devices. 10. Describe the operation of zener diodes, light-emit- ting diodes (LEDs), photovoltaic cells, photodi- odes, and varactor diodes. 11. Recognize NPN and PNP transistors. 12. Explain transistor biasing. 13. Describe transistor Alpha and Beta characteristics. 14. Explain the operation of JFET, MOSFET, and UJTs. SEMICONDUCTOR THEORY Chapter 1 pointed out that the electrons of a particu- lar atom are not an equal distance from the nucleus. They rotate in well-defined orbits. Each shell or orbit can hold only a certain number of electrons. Outer-shell electrons have a great deal to do with the electrical conductivity of an atom. Uncontrolled movement of these electrons causes certain atoms to be good electrical conductors.
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