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Introduction to Solids

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Introduction to Solids 3 Classes of Solids Amorphous No long range order Polycrystalline Order within grains Single Crystal Regular, repeated pattern Crystal Solid ... – PowerPoint PPT presentation

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Title: Introduction to Solids


1
Introduction to Solids
2
3 Classes of Solids
  • Amorphous
  • No long range order
  • Polycrystalline
  • Order within grains
  • Single Crystal
  • Regular, repeated pattern

3
Crystal Solid
  • Single crystal repetition of a unit cell
  • Crystal lattice
  • Array of corners of unit cells
  • Symmetry
  • Used to classify the crystal
  • Ex. Cubic symmetry

4
3 Subclasses of Cubic Crystals
  • Simple
  • The sites for atoms are at the corners of the
    cubes
  • Body-Centered-Cubic (bcc)
  • The sites for the atoms are at the corners of
    the cubes
  • Face-Centered-Cubic (fcc)
  • The sites for the atoms are at the corners and at
    the centers of each face of the cube
  • Note Show figures

5
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6
Crystal Structures
  • Diamond structure
  • Zincblende structure
  • Knowing the crystal structure, chemical
    composition and density of material, the
    following can be calculated
  • the length of the side of the unit cell
  • distance between centers of nearest neighbor
    atoms
  • Note Show figures

Structures of Si and GaAs
7
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8
Crystal Structures
  • X-ray diffraction
  • Method used to determine the plane and direction
    of a crystal
  • The specification of particular planes and
    directions is made through the use of Miller
    indices

9
  • Finding Milles indices of a plane in a crystal
  • Choose coordinate access along the principal
    directions in the crystal (long the unit cell
    edges)
  • Take the 3 numbers that result as the
    intersection of a plane with the 3 axes
  • Take their reciprocals
  • Multiply the results by the smallest value that
    will give 3 integers
  • These 3 integers are the Mille indices of the
    plane

10
  • Finding Milles indices of a direction in a
    crystal
  • Take the 3 components of a vector in that
    direction along the 3 axes
  • Multiply these components by whatever is needed
    to reduce them to the smallest set of integers
  • These integers are the Miller indices of the
    direction

11
  • Miller indices of a plane
  • (101) ? 101
  • Miller indices of a direction
  • 101 ? lt100gt
  • If negative, minus sign is placed over the integer

12
Two Types of Imperfections
  • Defects
  • The ideal unit cell repetition is interrupted in
    some way
  • Impurity
  • Occasional atoms of types other than the ones
    that make up the defined crystals unit cell.
  • Sometimes, intentionally introduced

13
Impurity
  • Doping adding impurities
  • Dopant the added material

14
Energy Level
  • Single atoms
  • Only one electron can occupy a given state
  • (Pauli exclusion principle)
  • Different states ? different energies associated
  • Ground state ? electrons of an atom are in the
    lowest possible energy states
  • Excited state ? when an electron moves to the
    state of higher energy

15
Energy Level
Nucleus ? protons neutrons
16
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17
Energy Level
  • Principal energy level
  • 123456
  • Sublevel
  • 1s2s 2p3s 3p 3d4s 4p 4d 4f5s 5p 5d 5f 5g6s
    6p 6d 6f 6g 6h

18
Energy Level
  • the 1s energy level is always the lowest energy
    level of all principal energy levels
  • for each principal energy level, the s sublevel
    is also the lowest energy sublevel
  • The diagram at the right illustrates the
    determination of order of sublevels by increasing
    energy

Source http//library.thinkquest.org/15567/lesson
s/2.html
19
Orbital

No. of sublevels No. of orbitals (s, p, d, f) Total No. of orbitals Maximum no. of electrons
1234 (1)(1, 3)(1, 3, 5)(1, 3, 5, 7) 14916 281832
  • A region within a sublevel where electrons may be
    found
  • In each orbital, there can be a maximum of two
    electrons
  • Each s sublevel has a single orbital
  • Each p sublevel has 3 orbitals
  • Each d sublevel has 5 orbitals
  • Each f sublevel has 7 orbitals
  • Thus, any s sublevel can have two electrons,
    while any p sublevel can have 6 electrons, and so
    on

20
Band Gap
Source http//hyperphysics.phy-astr.gsu.edu/hbase
/solids/band.html
21
Fermi-Level
  • Extra levels have been added by the impurities
  • In n-type material there are electron energy
    levels near the top of the band gap so that they
    can be easily excited into the conduction band
  • In p-type material, extra holes in the band gap
    allow excitation of valence band electrons,
    leaving mobile holes in the valence band

22
Video Links
  •  
  • CLASSES OF SOLIDS
  • http//www.youtube.com/watch?vSJsckwYxfgYfeature
    related
  •  
  • CRYSTAL LATTICE
  •  
  • Lattice Structures Part 1
  • (Cubic, body-centered, Face centered --gt unit
    cell)
  • http//www.youtube.com/watch?vRm-i1c7zr6Qfeature
    related
  •  
  • SAND TO SILICON TO IC
  • http//www.youtube.com/watch?vQ5paWn7bFg4
  • SILICON RUN 1
  • http//www.youtube.com/watch?vATt5dwdKt9I
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