《材料科学与工程基础》英文影印版习题及思考(19)

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12.23 Define the following terms as they pertain to semiconducting materials:

intrinsic, extrinsic, compound, elemental. Now provide an example of each. 12.24 Is it possible for compound semiconductors to exhibit intrinsic behavior?

Explain your answer.

12.25 For each of the following pairs of semiconductors, decide which will have the

smaller band gap energy Eg and then cite the reason for your choice: (a) ZnS and CdSe, (b) Si and C (diamond), (c) Al2O3 and ZnTe, (d) InSb and ZnSe, and (e) GaAs and AlP.

12.26 (a) In your own words, explain how donor impurities in semiconductors give

rise to free electrons in numbers in excess of those generated by valence

band–conduction band excitations. (b) Also explain how acceptor impurities give rise to holes in numbers in excess of those generated by valence

band–conduction band excitations.

12.27 (a) Explain why no hole is generated by the electron excitation involving a

donor impurity atom.

(b) Explain why no free electron is generated by the

electron excitation involving an acceptor impurity atom.

12.28 Will each of the following elements act as a donor or an acceptor when added

to the indicated semiconducting material? Assume that the impurity elements are substitutional.

12.29 (a) At approximately what position is the Fermi energy for an intrinsic

semiconductor?

(b) At approximately what position is the Fermi energy for an n-type

semiconductor?

(c) Make a schematic plot of Fermi energy versus temperature for an n-type semiconductor up to a temperature at which it becomes intrinsic. Also note on this plot energy positions corresponding to

the top of the valence band and the bottom of the conduction band.

The room-temperature electrical conductivity of a silicon specimen is 103

(_- m)_1. The hole concentration is known to be 1.0 _ 1023 m_3. Using the electron and hole mobilities for silicon in Table 12.2, compute the electron concentration. (b) On the basis of the result in part a, is the specimen intrinsic,