Callister - An introduction - 8th edition

720 • Chapter 18 / Electrical Properties
WHY STUDY the Electrical Properties of Materials?
Consideration of the electrical properties of materials
is often important when materials selection and processing
decisions are being made during the design of
a component or structure. For example, when we
consider an integrated circuit package, the electrical
behaviors of the various materials are diverse. Some need
to be highly electrically conductive (e.g., connecting
wires), whereas electrical insulativity is required of
others (e.g., the protective package encapsulation).
In the processing/structure/properties/performance
scheme for silicon semiconductors, reasons for studying
the electrical properties of materials are as follows:
• The electrical properties of semiconductors (e.g.,
silicon) are dependent on their electron band
structures—namely, electron energy states that are
occupied by electrons that are available to participate
in the conduction process. In this chapter we
introduce the concept of electrical conduction for
semiconductors from the perspective of their band
structures.
• We also discuss how the addition of atoms of specific
elements in minute concentrations affects the band
structure, and, in turn, the electrical characteristics
of a semiconductor.
• The electrical characteristics and mechanics of
operation of two different semiconducting devices
that are employed in integrated circuits are also
described and explained.
Learning Objectives
After studying this chapter you should be able to do the following:
1. Describe the four possible electron band structures
for solid materials.
2. Briefly describe electron excitation events that
produce free electrons/holes in (a) metals,
(b) semiconductors (intrinsic and extrinsic),
and (c) insulators.
3. Calculate the electrical conductivities of
metals, semiconductors (intrinsic and extrinsic),
and insulators given their charge carrier
density(s) and mobility(s).
4. Distinguish between intrinsic and extrinsic
semiconducting materials.
5. (a) On a plot of logarithm of carrier (electron,
hole) concentration versus absolute temperature,
draw schematic curves for both
intrinsic and extrinsic semiconducting
materials.
(b) On the extrinsic curve, note freeze-out,
extrinsic, and intrinsic regions.
6. For a p–n junction, explain the rectification
process in terms of electron and hole motions.
7. Calculate the capacitance of a parallel-plate
capacitor.
8. Define dielectric constant in terms of permittivities.
9. Briefly explain how the charge storing capacity
of a capacitor may be increased by the
insertion and polarization of a dielectric
material between its plates.
10. Name and describe the three types of
polarization.
11. Briefly describe the phenomena of ferroelectricity
and piezoelectricity.
18.1 INTRODUCTION
The prime objective of this chapter is to explore the electrical properties of materials,
that is, their responses to an applied electric field. We begin with the phenomenon
of electrical conduction: the parameters by which it is expressed, the mechanism of
conduction by electrons, and how the electron energy band structure of a material
influences its ability to conduct. These principles are extended to metals, semiconductors,
and insulators. Particular attention is given to the characteristics of semiconductors
and then to semiconducting devices. Also treated are the dielectric
characteristics of insulating materials. The final sections are devoted to the peculiar
phenomena of ferroelectricity and piezoelectricity.
720 •