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Chapter 11: Problem 54

Explain why the electrical conductivity of a semiconductor is significantly increased if trace amounts of either donor or acceptor atoms are present, but is unchanged if both are present in equal number.

Short Answer

Expert verified
Trace amounts of either donor or acceptor atoms in a semiconductor can significantly increase its conductivity as these can respectively donate electrons to the conduction band or accept electrons from the valence band, effectively increasing the number of charge carriers. However, if both donor and acceptor atoms are equally present, they neutralize each other's effects, thus leaving the conductivity unchanged.

Step by step solution

01

Understanding Semiconductors and Conductivity

In a pure semiconductor, the number of free charge carriers (electrons and holes) is determined by the intrinsic properties of the material, including the temperature. Electrons can move from the valence band to the conduction band, and this movement increases the electrical conductivity of the semiconductor.
02

Role of Donor and Acceptor Atoms

Impurities can alter the number of free charge carriers. A donor atom, with one more valence electron, can supply an extra electron to the conduction band when sufficiently energized. This increases the amount of free charge carriers and thus the conductivity. Acceptor atoms, with one less valence electron, are able to accept an electron from the valence band, leaving a hole. This hole behaves as a positive charge carrier and also increases the conductivity.
03

Equal Numbers of Donor and Acceptor Atoms

If there are an equal amounts of donor and acceptor atoms, an electron donated by a donor atom can be accepted by an acceptor atom. This transfer neutralises the effect of each type of dopant atom and the number of free charge carriers (and therefore the conductivity) remains the same as in the intrinsic semiconductor.

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Most popular questions from this chapter

102\. Which of the following species are paramagnetic? (a) \(\mathrm{B}_{2} ;\) (b) \(\mathrm{B}_{2}^{-} ;\) (c) \(\mathrm{B}_{2}^{+}\). Which species has the strongest bond?

The bond angle in \(\mathrm{H}_{2} \mathrm{Se}\) is best described as (a) between \(109^{\circ}\) and \(120^{\circ} ;\) (b) less than in \(\mathrm{H}_{2} \mathrm{S} ;\) (c) less than in \(\mathrm{H}_{2} \mathrm{S},\) but not less than \(90^{\circ} ;(\mathrm{d})\) less than \(90^{\circ}\)

In what type of material is the energy gap between the valence band and the conduction band greatest: metal, semiconductor, or insulator? Explain.

Represent bonding in the carbon dioxide molecule, \(\mathrm{CO}_{2},\) by \((\mathrm{a})\) a Lewis structure and \((\mathrm{b})\) the valencebond method. Identify \(\sigma\) and \(\pi\) bonds, the necessary hybridization scheme, and orbital overlap.

Construct a concept map that embodies the ideas of valence bond theory.
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