Solid State Physics I: Chap. 8

JAEJUN YUSEOUL NATIONAL UNIVERSITY

jyu@phya.snu.ac.kr

c©2001 JAEJUN YU

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Contents8 Semiconductors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

8.1 Band gaps. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68.2 Electrons and holes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .108.3 Intrinsic Carriers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .158.4 Impurity Conductivity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .218.5 Diodes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30

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8. SemiconductorsIn the previous chapter, it was shown that the Fermi level can lie at the bandgap depending on the number of electrons in the unit cell, where the fullyoccupied valence bands are separated from the fully unoccupied conductionbands by a finite band gap. Thus, at absolute zero temperature, a pure perfectcrystal of most semiconductors will be an insulator.

However, in a class of materials called “semiconductors”, the size of the bandgap Eg is relatively small compared to the energy scale of room temperatureTr = 200 K so that even a highly purified semiconductor exhibits intrinsic con-ductivity due to the sufficiently high thermal population of electrons-and-holescarriers in the conduction-and-valence bands.

In addition, when doped, the semiconductors show interesting physical charac-teristics which are useful for device applications such as transistors, switches,diodes, phtovoltaic, detectors, thermistors, and lasers. In this chapter, webriefly the basic physical features of semiconductors.

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The topics to be discussed in this chapter include:

• Band gaps

• Electrons and holes

• Intrinsic Carriers

• Impurity conductivity

• Diode

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Suggestions for further readings

• Ashcroft/Mermin, Chap. 28 and 29

• Kittel, Chap. 8

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8.1. Band gaps

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8.2. Electrons and holes

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8.3. Intrinsic Carriers

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8.4. Impurity Conductivity

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8.5. Diodes

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