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Figure 16.31: Two-dimensional representations of (a) a quartz crystal and (b) a quartz glass.
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Figure 16.28: The p orbitals (a) perpendicular to the plane of th carbon ring system in graphite can combine to form
(b) an extensive pie bonding network.
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The Electronic Configuration of a Magnesium Atom
n l ml ms
3 0 0 +1/2
3 0 0 -1/2
Mg: (Ne)3s2
1s
2s
3s2p
3p
Empty 3p orbitals in Mg valence shell
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Orbital energy levels
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Figure 16.24: A representation of the energy levels (bands) in a magnesium crystal
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Figure 16.27: Partial representation of the MO energies in (a) diamond and (b) a typical metal
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Electron sea model for metals
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Bonding in SolidsBonding in SolidsMetallic SolidsMetallic Solids
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Band structure of Semiconductors
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Band Diagram: Semiconductor with No Doping
• At T = 0, lower valence band is filled with electrons and upper conduction band is empty, leading to zero conductivity.– Fermi energy EF is at midpoint of small energy gap (<1 eV)
between conduction and valence bands.
• At T > 0, electrons thermally “excited” from valence to conduction band, leading to measurable conductivity.
EF
EC
EV
Conduction band(Partially Filled)
Valence band(Partially Empty)
T > 0
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Silicon Crystal Doped with (a) Arsenic and (b)
Boron
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Figure 16.33: Energy-level diagrams for (a) an n-type semiconductor and (b) a p-type semiconductor.
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pn junction
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Figure 16.34: The p-n junction involves the contact of a p-type and an n-type semiconductor.
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PN Junction - 7
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PN Junction with Applied Potential
No current, Barrier Larger Current Flows, Barrier Smaller
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A schematic of two circuitsconnected by a transistor.
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Photolithography to make semiconductorintegrated circuits
http://britneyspears.ac/physics/fabrication/photolithography.htm
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(a)-(h) The steps for forming a transistor in a crystal of initially pure silicon.
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(a)-(h) The steps for forming a transistor in a crystal of initially pure silicon. (cont’d)
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Solar Cells
n-typep-type
Photons
Electron
Hole
Load
p-n Junction under Illumination
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Solar Panels – Photovoltaic Cells
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Schematic of a Photovoltaic (solar) cell
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Herbert Kroemer
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Light Amplification by Stimulated Emission Radiation
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Semiconductors – key points to remember
• Band structure: Valence band – gap – conduction band
•DOPING: Group V n type, Group III p type
•n-p junctions
•Devices: (LED, laser, transistor, solar cell)
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Ionic liquids
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