Lundstrom ECE 305 S16
ECE-305: Spring 2015
Week 1 Recap
Professor Mark Lundstrom Electrical and Computer Engineering
Purdue University, West Lafayette, IN USA [email protected]
1/19/16
Pierret, Semiconductor Device Fundamentals (SDF) pp. 23-32
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Announcements
Lundstrom ECE 305 S16
1. Exam 1: Thurs, 1/28 PHYS 112 6:30 – 7:30 PM see the class homepage for info https://nanohub.org/groups/ece305S16
2. Do the homework!
3. Review the quizzes.
4. Ask questions on Piazza and/or in office hours
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silicon energy levels
1S2
2S2
2P6
3S2
3P2
4S0
Si atom (At. no. 14)
4 valence electrons 8 valence states
“core levels”
Lundstrom ECE 305 S16
ener
gy
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silicon energy levels / energy bands
Natoms ≈ 5×1022 cm-3
5.43 A
4 nearest neighbors
Lundstrom ECE 305 S16
In a solid, energy levels become energy bands.
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silicon energy levels à energy bands
Si crystal
Lundstrom ECE 305 S16
3S2
3P2
Si atom (At. no. 14)
ener
gy
4Natoms states conduction “band”
valence “band” 4Natoms states
“forbidden gap”
• • • • • • • • •
• • • • • • • • •
E = 3
2kBT = 0.026 eV
T = 300 K
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optical generation
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EC
EV
EG = 1.1eV Eph = hf >> EG
KEe
KEh
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“energy band diagrams”
Lundstrom ECE 305 S16
conduction “band”
valence “band”
“forbidden gap”
• • • • • • • • •
• • • • • • • • • EC
EV
EG
n0 = p0 = ni cm-3
“intrinsic semiconductor”
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energy band diagrams
Lundstrom ECE 305 S16
“Whenever I teach my semiconductor device physics course, one of the central messages I try to get across early is the importance of energy band diagrams. I often put this in the form of “Kroemer’s lemma of proven ignorance”:
If, in discussing a semiconductor problem, you cannot draw an Energy Band Diagram, this shows that you don’t know what you are talking about.
If you can draw one, but don’t, then your audience won’t know what you are talking about.
corollary:
(Nobel Lecture, 2000)
EG Si( ) = 1.1eV
EG GaAs( ) = 1.4 eV
EG Ge( ) = 0.66 eV
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Bandgap in intrinsic carrier concentration
Lundstrom ECE 305 S16
Intrinsic Si
EC
EV
EG = 1.1eV
n = ni = 1010cm−3
p = ni = 1010cm−3
n = p = ni
ni Si( ) = 1×1010 cm−3 T = 300 K( )
ni GaAs( ) = 2×106 cm−3 T = 300 K( )
ni Ge( ) = 2×1013 cm−3 T = 300 K( )
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Electrons and holes
Lundstrom ECE 305 S16
The first semiconductor textbook. (1950)
another view
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1) Electrons in the conduction band can move 2) Holes in the valence and can move 3) Electrons and holes can recombine
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Recombination: energy band diagrams
Lundstrom ECE 305 S16
Intrinsic Si
EC
EV
EG = 1.1eV
Question: If an electron and hole recombine in GaAs, what color light is emitted?
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outline
✔ 1. Quantization of energy levels
2. Energy bands
3. Electrons and holes
4. Insulators, metals, and semiconductors
✔ ✔
metals insulators and semiconductors
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metals: conduct electricity (and heat) well. insulators: don’t conduct electricity well
usually don’t conduct heat well semiconductors: in-between, but
their properties can be controlled
Lundstrom ECE 305 S16
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insulators metals semiconductors
Lundstrom ECE 305 S16
EV
filled states
EC
empty states
EG ≈ 9 eV (SiO2 )
kBT ≈ 0.026 eV (300K)
empty states
filled states
EBOT
ETOP
filled states
EC
empty states
EG ≈1.1eV (Si)
EV
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outline
✔ 1. Quantization of energy levels
2. Energy bands
3. Electrons and holes
4. Insulators, metals, and semiconductors
✔ ✔ ✔
Lundstrom ECE 305 S16 17
vocabulary
1) Crystalline 2) Amorphous 3) Polycrystalline 4) Bravais lattices 5) Unit cell 6) Primitive unit cell 7) Diamond lattice 8) Zinc blende lattice 9) Miller indices
10) Energy levels 11) Energy bands 12) Forbidden gap (bandgap) 13) Conduction band 14) Valence band 15) Electrons (in the conduction band) 16) Holes (in the valence band) 17) Optical generation 18) Thermal generation 19) Metal 20) Insulator 21) Semiconductor
