EE 362 Electric and Magnetic Properties of Materials

1
EE 362 Electric and Magnetic Properties of
Materials

• Dr. Brian T. Hemmelman
• Chapter 1 Slides

2
Types of Materials (2)

• Materials can be classified as
• Conductors Easily conduct current
• Insulators Do not conduct significant current
• Semiconductors Conductivity between conductors
  and insulators
• Superconductors Zero resistance below critical
  temperature

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Types of Materials (3)

• Specialty areas concerned with liquid, gaseous,
  and plasma states (LCDs, gas lasers, plasma
  hydrodynamics).
• Most current electronic materials though are
  solids.

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Types of Solids (4)

• Crystalline Have ordered atomic or molecular
  structure throughout.
• Polycrystalline Have order within grains, but
  grain orientation is random.
• Amorphous Have no order or very short range
  order.

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Types of Solids (5)
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Solid Electronic Materials (6)

• Conductors insulators, amorphous
  polycrystalline organic materials are all
  important.
• We will focus on crystalline semiconductors
  (diodes, transistors, CCDs, solar cells, etc.).

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Crystalline Semiconductors (7)

• Elemental Semiconductors Composed of only one
  element
• Silicon Si
• Germanium Ge
• Compound Semiconductors Composed of two or more
  different elements
• Gallium Arsenide GaAs
• Indium Phosphide - InP

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Crystal Structures (8)

• Unit Cell A small volume that can be used to
  reproduce the entire crystal (through translation
  only, no rotation).
• Primitive Cell Smallest unit cell that can be
  used to repeat (not always the most appropriate
  to visualize or describe a crystal structure).

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Primitive Unit Cell (9)
All equivalent lattice sites can be found with
where p, q, and s are integers.
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The 14 Bravais Lattices (10)
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The 14 Bravais Lattices (11)
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The 14 Bravais Lattices (12)
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The 14 Bravais Lattices (13)
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The 14 Bravais Lattices (14)
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Silicon A Diamond Lattice (15)
Two interpenetrating face-centered cubic lattices
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Gallium Arsenide Zincblende (16)
a is defined as the lattice constant (usually
in Angstroms)
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The Diamond/Zincblende Lattice (17)

• http//web.cecs.pdx.edu/vanhalen/courses/applets/
  silicon.html

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Miller Indices (18)

• We need to keep track of atomic planes and
  orientations inside the crystal.
• Miller indices are a way to reference these
  atomic planes and directions.
• We use the intercepts of the unit cell in terms
  of the integers p, q, and s.

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Typical Crystal Planes (19)
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Determining Miller Indices (20)

• Find x, y, z axis intercepts in terms of
  integer unit quantities (does not have to be in
  terms of lattice constant a).These intercepts
  are (d e f).
• Invert each member of the triplet

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Determining Miller Indices (21)

• Multiply through by smallest integer needed to
  make all values in the triplet into
  integers.The resulting integers are the Miller
  indices (h k l).

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Determining Miller Indices (22)

• Determine intercepts(1 3 1)
• Invert each of these(1/1 1/3 1/1)
• Multiply through by 3 to convert all values to
  integers(3 1 3)
• This is a (3 1 3) plane.

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Determining Miller Indices (23)

• Determine intercepts(4 2 4)
• Invert each of these(1/4 1/2 1/4)
• Multiply through by 4 to convert all values to
  integers(1 2 1)
• This is a (1 2 1) plane

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Crystal Directions (24)

• Crystal directions are also defined based on
  Miller indices.
• A crystal direction is defined by a vector that
  is normal (perpendicular) to the crystal plane
  defined by a particular set of Miller indices.

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Crystal Directions (25)
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Atomic Surface Density Example (26)
Total number of atoms in this area is 1 4(1/4)
2 atoms Surface area is (a1)(1.414a1)
1.414a12 If the lattice constant is a1 5
Angstroms 510-8 cm then Surface density is (2
atoms)/(1.414(510-8 cm)2) 5.661014 atoms/cm2
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Silicon Ingot Wafers (27)
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Atomic Bonds (28)

• Ionic Bonding Some atoms lose electrons
  (become ion) and some atoms gain electrons
  (become - ion).Usually atoms from opposite
  sides of the periodic chart form ionic bonds.
  For example, sodium chloride (NaCl).

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Atomic Bonds (29)

• Covalent Bonding Atoms share electrons to
  form complete outer shells.Usually atoms from
  middle groups of the periodic chart, e.g. Group
  III Group V, but also hydrogen molecule.

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Atomic Bonds (30)

• Metallic Bonds Many atoms with few valence
  electrons (Groups I, II, and III) cluster to
  share electrons and achieve a low energy
  state.Essentially becomes a bunch of nuclei
  surrounded by a sea of loosely bound electrons.

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Atomic Bonds (31)

• Van der Waals Some compounds may form through
  ionic bonds, but this can create an imbalance of
  charge in the molecule and establish a dipole
  (e.g. HF).There can then be electrostatic
  interactions between molecular dipoles that cause
  the molecules to cluster into a solid.