Chapter 2 Characteristics of Semiconductor Materials

1
Chapter 2 Characteristics of Semiconductor
Materials

2
Objectives

• After studying the material in this chapter, you
  will be able to
• 1. Describe the atom, including valence shell,
  band theory and ions.
• 2. Interpret the periodic table with regards to
  main group elements and explain how ionic and
  covalent bonds are formed.
• 3. State the three classes of materials and
  describe each one with regards to current flow.
• 4. Explain resistivity, resistance, capacitance
  and discuss their importance to wafer
  fabrication.
• 5. Describe pure silicon and give four reasons
  why it is the most common semiconductor material.
• 6. Explain doping and how the trivalent and
  pentavalent dopant elements make silicon a useful
  semiconductor material.
• 7. Explain p-type (acceptor) silicon and n-type
  (donor) silicon, how silicon resistivity changes
  with the addition of a dopant, and the PN
  junction.
• 8. Discuss alternative semiconductor materials,
  with emphasis on gallium arsenide.

3
Atomic Structure

• Matter
• Element
• Nucleus
• Proton
• Neutron
• Orbital Shell
• Electron
• Molecule
• Compound

• Electrons
• Electron Energy
• Valence Shells
• Energy-Band Theory
• Ions

4
Elementary Model of the Carbon Atom
Figure 2.1
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Electron Shells in Atoms
Figure 2.2
6
Electron Shells for Sodium and Chlorine Atoms
Figure 2.3
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Energy Band Gaps
Figure 2.4
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Sodium Chloride
Figure 2.5
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The Periodic Table

• Characteristics of Commonly Used Elements
• Ionic Bonds
• Covalent Bonds

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The Periodic Table of the Elements
Figure 2.6
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Element Box of the Periodic Table
Figure 2.7
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Characteristics of Chemicals used in Wafer
Fabrication
Continued on next slide
Table 2.1
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Characteristics of Chemicals used in Wafer
Fabrication(continued)
Table 2.1
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Ionic Bond for NaCl
Figure 2.8
15
Covalent Bond for HCl
Figure 2.9
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Classifying Materials

• Conductors
• Insulators
• Semiconductors

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Electrical Current Flow
Figure 2.10
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Flow of Free Electrons in Copper
Copper atom
Figure 2.11
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How Sizes Affect Resistance
Figure 2.12
20
Adding an Impurity to Water to Improve its
Conductivity
Figure 2.13
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Basic Capacitor Structure

• K, dielectric constant in farads/cm
• A, plate area in cm2
• S, spacing between plates in cm

Figure 2.14
22
Battery Charges a Capacitor
Figure 2.15
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Capacitor Holds a Charge
Figure 2.16
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Low-k Dielectric Material
Figure 2.17
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Silicon

• Pure Silicon
• Why Use Silicon?
• Doped Silicon
• Dopant Materials
• n-type Silicon
• p-type Silicon
• Resistivity of Doped Silicon
• pn Junctions

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Group IVA Elemental Semiconductors
Figure 2.18
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Covalent Bonding of Pure Silicon
Figure 2.19
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SiO2 on Silicon Wafer
Figure 2.20
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Doping of Silicon
Figure 2.21
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Silicon Dopants
Figure 2.22
31
Electrons in N-Type Silicon with Phosphorus Dopant
Figure 2.23
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Conduction in n-Type Silicon
Figure 2.24
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Holes in p-Type Silicon with Boron Dopant
Figure 2.25
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Conduction in p-Type Silicon
Figure 2.26
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Silicon Resistivity Versus Dopant Concentration
Redrawn from VLSI Fabrication Principles, Silicon
and Gallium Arsenide, John Wiley Sons, Inc.
Figure 2.27
36
Cross Section of Planar pn Junction
Figure 2.28
37
Alternative Semiconductor Materials
Table 2.3
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Chapter 2 Review

• Summary 41
• Key Terms 41
• Review Questions 42
• References 42