EE 105 Semiconductors - University of California, Berkeley 105 Lecture 2: Semiconductors B. E. Boser...
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B. E. Boser 1
EE 105
Semiconductors
Bernhard E. Boser
University of California, Berkeley
Copyright © 2012 by Bernhard Boser
EE 105 Lecture 2: Semiconductors
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Active Devices
• Control (current) flow
• Cascadeable:
– Compatible inputs and outputs including
– Same physical domain, e.g.
• Electrical
• Pneumatic
• Chemical
• Mechanical
– Compatible signal levels, e.g.
• Switch with 5V control signal must be able to switch 5V at output
• Examples:
– Transistor
– Relays
– Vacuum tube
EE 105 Lecture 2: Semiconductors
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Semiconductors
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Electrical Conduction
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Atom Shells
EE 105 Lecture 2: Semiconductors
Si
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Semiconductors
EE 105 Lecture 2: Semiconductors
III IV V
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Silicon Crystal
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Silicon Crystal
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Density:
5 x 1022 atoms / cm3
Distance between atoms:
0.235 nm
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2D Representation for Simplicity
EE 105 Lecture 2: Semiconductors
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Bandgap
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Intrinsic Carrier Concentration ni
EE 105 Lecture 2: Semiconductors
40 20 0 20 40 60 801 10
6
1 107
1 108
1 109
1 1010
1 1011
1 1012
1012
106
n i T x T 0
cm3
8555 T x
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Semiconductors Summary
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Drift Current
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Current Flow
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Mobility
EE 105 Lecture 2: Semiconductors
Electron drift velocity in Si
Jacoboni, C., C. Canali, G. Ottaviani, and A. A. Quaranta,
Solid State Electron. 20, 2(1977) 77-89.
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Drift Current Example
EE 105 Lecture 2: Semiconductors
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Holes
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“Semi” Conductor?
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Donors
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Question
Is a doped semiconductor charge neutral?
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Uniform Semiconductors Summary
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pn Junction
(Diode)
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pn Junction
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n = ND p = NA
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Depletion Region
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Drift and Diffusion Currents
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+ Idrift,n = 0A
Idiffusion,n
n = ND p = NA
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Junction Potential
EE 105 Lecture 2: Semiconductors
http://en.wikipedia.org/wiki/P-n_junction
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Reverse Bias
EE 105 Lecture 2: Semiconductors
Ref: R. Howe, Prentice Hall.
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Forward Bias
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Putting it all Together
EE 105 Lecture 2: Semiconductors
