p42_040.pdf

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Chapter 42 - 42.40

40. (a) n -type, since each phosphorous atom has one more valence electron than a silicon atom.

(b) The added charge carrier density is n P =10 − 7 n Si =10 − 7 (5

10 28 m − 3 )=5

10 21 m − 3 .

10 5 . Here the factor of 2in the denominator

reﬂects the contribution to the charge carrier density from both the electrons in the conduction

band and the holes in the valence band.

10 21 m − 3 ) / [2(5

10 15 m − 3 )] = 5