Technology & Engineering
n type Semiconductor
An n-type semiconductor is a type of material that has been doped with elements that provide an excess of negative charge carriers, typically electrons. This results in the semiconductor having an overall negative charge. N-type semiconductors are commonly used in electronic devices and integrated circuits, where they play a crucial role in the functioning of transistors and other components.
Written by Perlego with AI-assistance
Related key terms
1 of 5
7 Key excerpts on "n type Semiconductor"
eBook - PDF- Geoff Lewis(Author)
- 2013(Publication Date)
- Newnes(Publisher)
The basic materials that are employed have a con-ductivity about halfway between that of conductors and insulators, hence the term semiconductor. These include: germanium (Ge), silicon (Si) and the Group III/V elements, aluminium (Al), gallium (Ga), indium (In) / arsenic (As), antimony (Sb) Semiconductor devices and technology 285 Germanium is now less used than silicon because of its poorer temperature characteristics (typical operating temperature 75°C compared with 200°C for silicon). 32.1 Behaviour of PN junctions Just as controlled conduction can be achieved through doping intrinsically pure tetravalent semiconductor elements (I type material) with trivalent or pentavalent impurities in a precisely controlled way, pseudo-semiconduction can be produced by the careful combination of the Group III (trivalent) and Group V (pentavalent) elements to produce a new class of device with even more useful characteristics. By adding pentavalent impurity atoms to I type material, addi-tional electrons are donated to the crystal structure. This forms an Ν type semiconductor material in which electrons form the majority current carriers. In a similar way, the addition of trivalent impurities leaves spaces or holes in the crystal structure which represent energy levels where electrons could exist. This Ρ type material thus has the positive charges of the holes as majority carriers. A hole therefore has an equal but opposite polarity charge to that of an electron. In both Ρ and Ν type materials there will always be some thermally generated charges of the opposite polarity and these are known as minority carriers. In certain applications, the Ρ and Ν type impurity layers may be doped to a relatively higher or lower level than normal. By convention, these regions would be indicated as P + or N + ; or P~ or N, respectively.
eBook - PDFElectronics—From Theory Into Practice
Pergamon International Library of Science, Technology, Engineering and Social Studies
- J. E. Fisher, H. B. Gatland, P. Hammond(Authors)
- 2014(Publication Date)
- Pergamon(Publisher)
CHAPTER 1 The Semiconductor INTRODUCTION A semiconductor material is one having a specific resistance inter-mediate between that of an insulator and a conductor, the value of which increases rapidly with rising temperature. Considering the atomic structure of such material, if sufficient energy is provided, by heating for instance, electrons will be released from their nuclei, each leaving behind it a hole. Under the influence of an electric field, an electric current will flow, which may be regarded as a movement of electrons in one direction and a movement of holes in the opposite direction. In the case of a pure or intrinsic semiconductor the numbers of holes and free electrons are always equal. The two materials which have been most commonly used are germanium and silicon, both of which come from chemical Group IV. Gallium arsenide, however, is a material which is now being used in ever increasing fields of application. If a semiconductor is doped with an element from Group V, say arsenic, the equality of free electrons and holes will no longer exist, there being an excess of free electrons. An electric current through such a material will then consist mostly of a flow of electrons in one direction and relatively few holes moving in the opposite direction. In this case the electrons are called majority carriers and the holes, minority carriers. A semiconductor doped in this way is known as H-type material since the majority carriers possess negative charge. A similar state of affairs will occur if the semiconductor is doped with an element such as indium from Group III. However, in this case an excess of holes will exist and these are the majority carriers. Since the majority carrier possesses positive charge such a material is known as p type. In the production of semiconductor devices, it is often required that the level of doping be controlled. The more heavily doped a material is, the lower is its resistivity.
eBook - ePub- Geoff Lewis(Author)
- 2013(Publication Date)
- Routledge(Publisher)
intrinsically pure tetravalent semiconductor elements (I type material) with trivalent or pentavalent impurities in a precisely controlled way, pseudo-semi-conduction can be produced by the careful combination of the Group III (trivalent) and Group V (pentavalent) elements to produce a new class of device with even more useful characteristics. By adding pentavalent impurity atoms to I type material, additional electrons are donated to the crystal structure. This forms an n type Semiconductor material in which electrons form the majority current carriers.In a similar way, the addition of trivalent impurities leaves spaces or holes in the crystal structure which represent energy levels where electrons could exist. This P type material thus has the positive charges of the holes as majority carriers. A hole therefore has an equal but opposite polarity charge to that of an electron. In both P and N type materials there will always be some thermally generated charges of the opposite polarity and these are known as minority carriers.In certain applications, the P and N type impurity layers may be doped to a relatively higher or lower level than normal. By convention, these regions would be indicated as P+ or N+ ; or P– or N–, respectively.If a surface of a mono-crystalline P type material is heated to about 1100°C and exposed long enough to a gaseous atmosphere of N type impurity, the surface will be converted into N type. Therefore, somewhere below the surface, there will exist a junction on an atomic scale, between the P and N type materials. Holes and electrons will migrate across this junction to produce an electric field described as the barrier potential. When this reaches some particular level (about lOOmV for Ge and 600 mV for Si), the region becomes depleted of free current carriers to produce a barrier or depletion region as indicated in Fig. 32.1 . If an external voltage greater than the barrier potential, is now applied to this junction with a positive polarity on the P region (forward bias), current will flow through the junction and in the external circuit. If the applied voltage is reversed, the barrier potential is reinforced and very little current flows (reverse bias). This current would in fact fall to zero if it were not for the thermally generated hole-electron pairs that act as minority carriers. Operated in this way, the PN junction thus has diode characteristics which, in many cases, can conveniently be considered simply as a piecewise
- Gabor L. Hornyak, H.F. Tibbals, Joydeep Dutta, John J. Moore(Authors)
- 2008(Publication Date)
- CRC Press(Publisher)
F IG . 17.8 p-Type substitutional doping with gallium (Ga) atoms in a silicon (Si) lattice. Three of the valence electrons of Ga bind to neigh-boring Si atoms leaving a hole for conduction. Si Si Si Si Ga Si Ga Si Si Si Si Ga Si Si Si Electron hole Electron hole Electron hole F IG . 17.7 Energy level diagram of a typical p-type semiconductor. Here E Fi is the Fermi level of an intrinsic semiconductor. CB E c E F i E a E v VB 942 Introduction to Nanoscience and Nanotechnology In the band structure picture, impurity states are created much closer to the valence band. These states are known as acceptors, since they can accept elec-trons from the valence band. Again, it is much easier to “liberate” the electron for conduction at lower thermal energy. A semiconductor doped with acceptors is known as a “p-type” semiconductor (p for positive charge carrier). Doping changes the resistivity of semiconductors drastically. A typical exam-ple of antimony-doped germanium with different antimony concentrations and its relative resistivity is shown in Table 17.6 above. A diode is created when a p-type material is joined to an n-type material to create a p/n-junction ( Fig. 17.1) . The p-type material will have a high concentration of holes and few electrons. The n-type material will have a high concentration of electrons and few holes. It is obvious that there will be a large concentration gradient of both free electrons and free holes. Therefore there must be a large electric field in the p/n-junction region, which will oppose the tendency of the electron and hole concentrations to even themselves out. As previously mentioned this electric field arises when the carriers diffuse down their concentration gradi-ents. As they do so they uncover (remove the screening carriers from) the fixed doping atoms, which have positive and negative charges for donors (n-type) and acceptors (p-type), respectively.
eBook - ePubFundamentals of Electroceramics
Materials, Devices, and Applications
- R. K. Pandey(Author)
- 2018(Publication Date)
- Wiley-American Ceramic Society(Publisher)
7 Elements of A Semiconductor Chapter Menu 7.1 Introduction 7.2 Nature of Electrical Conduction in Semiconductors 7.3 Energy Bands in Semiconductors 7.4 Origin of Holes and n‐ and p‐Type Conduction 7.5 Important Concepts of Semiconductor Materials 7.6 Experimental Determination of Semiconductor Properties Problems Science is not only a discipline of reason but, also, one of romance and passion. Stephen Hawking 7.1 Introduction Semiconductor materials dominate modern electronics and microelectronics technology and have greatly influenced our civilization. Their impact is second to none in each and every aspect of our lives. There is hardly any device that we use in our daily life that has remained immune from the impact of semiconductors be it a child's simple toy or a spaceship exploring the universe in quest of knowledge. We all are familiar with the words diode, transistors, electronic switches, amplifiers, etc. They are ubiquitous in our lives, and it is hard to imagine how the modern society could even function without these wonder devices. We use a block diagram shown in Figure 7.1 to introduce our readers to the essential elements of semiconductor materials and devices. It is nevertheless just a brief representation of the field and, by no means, can the vastness of semiconductor technology be encompassed in one single figure. We have tried to do justice to this subject in this chapter particularly in describing the theoretical aspect of the semiconductor phenomenon relevant to the understanding of the nature and properties of electroceramic semiconductors that we will cover in the next chapter
- 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).
- Wei Gao, Zhengwei Li;Nigel Sammes;;(Authors)
- 2011(Publication Date)
- WSPC(Publisher)
Fig. 5.5 Conductivity σ versus 1/T for Si and Ge (source: L.A.A. Warnes, “Electronic Materials”, Macmillan Education Ltd. 1990). 10 -4 10 -2 10 -0 10 2 10 4 0.8 1.6 2.4 3.2 4.0 σ (S/m) Si Ge 300K 1000 T -1 (K -1 ) 96 Introduction to Electronic Materials for Engineers Fig. 5.6 Schematics showing electron excitation in Si (a) and Ge (b). 5.4 Extrinsic Semiconductor One of the main reasons that semiconductors are useful in electronics is that their properties can be altered in a controllable way by adding small amounts of impurities. These impurities are called dopants. Heavily dop-ing a semiconductor can increase its conductivity by a factor greater than a billion. In modern integrated circuits, for instance, heavily-doped poly-crystalline silicon is often used as a replacement for metals. An extrinsic semiconductor is a semiconductor that has been doped with impurities to modify the number and type of free charge carriers present. 5.4.1 n-type extrinsic semiconductors The purpose of n -type doping is to produce an abundance of mobile or “carrier” electrons in the material. If an atom with five valence electrons, such as phosphorus (P), arsenic (As), or antimony (Sb), is incorporated into the crystal lattice in place of a Si atom, then that atom will have four covalent bonds and one unbonded electron. This • • • • • • ° ° • • ° ° • • • • • • • • • • • • ° • • • • • • • • • • • • 300 K E c E v • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • E f 1.12eV E c E v 0 K (a) • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • E f 0.6 7 eV E c E v 0 K • ° • • • • • ° ° • • ° ° • • ° • • • • • ° • • • ° • • • • • • • • • • • 300 K E c E v • • • (b) Semiconductor, Properties and Materials 97 extra electron is only weakly bound to the atom; and this new state of bonding energy is rather low, ~0.01 eV. It can then be easily excited into the conduction band. At room temperatures, virtually all such electrons are excited into the conduction band.
Index pages curate the most relevant extracts from our library of academic textbooks. They’ve been created using an in-house natural language model (NLM), each adding context and meaning to key research topics.
