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Callister - An introduction - 8th edition

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772 • Chapter 18 / Electrical Properties<br />

Processing/Structure/Properties/Performance Summary<br />

Relative to the processing, in Chapter 5 we discussed principles of diffusion as they<br />

apply to semiconductors (specifically silicon). In some instances, doping of impurity<br />

atoms (which makes the semiconductor extrinsic) is accomplished by diffusion.<br />

The following diagram illustrates these relationships.<br />

Nonsteady-state diffusion<br />

(Chapter 5)<br />

Silicon<br />

Semiconductors<br />

(Processing)<br />

Specification of composition<br />

(Chapter 4)<br />

Temperature dependence<br />

of diffusion coefficient<br />

(Chapter 5)<br />

Diffusion in<br />

semiconductors<br />

(Chapter 5)<br />

Doping of semiconductors<br />

(Chapter 18)<br />

One of the important structural elements of semiconductors is electron band<br />

structure. We discussed this concept as well as band structures for both intrinsic and<br />

extrinsic materials. Band structure, to some degree, is due to the covalent (or predominantly<br />

covalent) interatomic bonding, which, in turn, is a consequence of the<br />

electron configuration of the semiconductor (Chapter 2). These relationships are<br />

noted in the following diagram.<br />

Silicon<br />

Semiconductors<br />

(Structure)<br />

Electron configuration:<br />

Si<br />

(Chapter 2)<br />

Covalent interatomic<br />

bonding<br />

(Chapter 2)<br />

Intrinsic electron<br />

band structure<br />

(narrow band gap)<br />

(Chapter 18)<br />

Extrinsic electron<br />

band structure<br />

(donor/acceptor<br />

levels)<br />

(Chapter 18)<br />

For both intrinsic and extrinsic semiconduction, electrical conductivity is a function<br />

of both carrier concentration and mobility of the carriers (electrons and/or<br />

holes). Both carrier concentration and mobility depend on temperature and impurity<br />

content. We note these relationships in the following diagram.<br />

Temperature dependence,<br />

carrier concentration<br />

Silicon<br />

Semiconductors<br />

(Properties)<br />

Electrical conductivity<br />

(definitions)<br />

Intrinsic semiconduction<br />

Electron/hole mobilities,<br />

factors that affect<br />

Extrinsic semiconduction

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