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1.5: Summary

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    25310

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    In this chapter we have examined the basic structure of atoms. This includes the concept of electron shells and permissible energy states. We have used both the Bohr model of the atom and the corresponding energy band diagrams.

    Crystals such as silicon show a very ordered three dimensional structure that relies on strong covalent bonds. The crystal tends to “fuzz” or broaden the permissible energy levels into thicker energy bands. Further, the crystal exhibits a modest energy gap, or band gap, between the valence band and conduction band. This gap is much smaller than the gap seen in insulators, and therefore the material is referred to as a semiconductor, being somewhere between a true conductor and a true insulator.

    The electrical characteristics of a pure, or intrinsic, semiconductor crystal can be altered by adding impurities or dopants. A doped crystal is referred to as an extrinsic crystal. If a pentavalent dopant is added, there will be a surplus of electrons and a raising of the Fermi level. The new crystal is called N-type material. In contrast, if a trivalent dopant is added, there will be a surplus of holes and a lowering of the Fermi level. The new crystal is called P-type material. In N-type material, electrons are the majority charge carrier and holes are the minority charge carrier. In P-type material, holes are the majority carrier while electrons serve as the minority carrier.

    1.5.1: Review Questions

    1. Describe the differences between a conductor, an insulator and a semiconductor.

    2. Define the terms Fermi level, valence band, conduction band and band gap.

    3. What is the fundamental difference between an intrinsic crystal and an extrinsic crystal?

    4. What is meant by the term doping?

    5. What is the effect of donor and acceptor impurities on the Fermi level?

    This page titled 1.5: Summary is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by James M. Fiore via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.