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Callister - An introduction - 8th edition

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780 • Chapter 18 / Electrical Properties<br />

comparing the properties and applications<br />

(and/or potential applications) of silicon<br />

and gallium arsenide.<br />

Conduction in Ionic Materials<br />

18.D8 Problem 18.47 noted that FeO (wüstite)<br />

may behave as a semiconductor by virtue of<br />

the transformation of Fe 2 to Fe 3 and the<br />

creation of Fe 2 vacancies; the maintenance<br />

of electroneutrality requires that for every<br />

two Fe 3 ions, one vacancy is formed. The<br />

existence of these vacancies is reflected in<br />

the chemical formula of this nonstoichiometric<br />

wüstite as Fe (1x) O, where x is a small<br />

number having a value less than unity. The<br />

degree of nonstoichiometry (i.e., the value<br />

of x) may be varied by changing temperature<br />

and oxygen partial pressure. Compute<br />

the value of x that is required to produce an<br />

Fe (1x) O material having a p-type electrical<br />

conductivity of 2000 ( # m) 1 ; assume that<br />

the hole mobility is 1.0 10 5 m 2 /V#<br />

s, the<br />

crystal structure for FeO is sodium chloride<br />

(with a unit cell edge length of 0.437 nm),<br />

and the acceptor states are saturated.

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