Si as a Semiconductor Material
UC San Diego Jacobs School of Engineering
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N-type Semiconductor Materials
UC San Diego Jacobs School of Engineering
N-type Si has an extra electron for each dopant atom,
This electron is mobile
2
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P-type Semiconductor Materials
UC San Diego Jacobs School of Engineering
P-type Si has a “hole” (i.e a missing electron) that acts like
A mobile positive charge
3
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P-N Junction formed by joining p & n type
materials
UC San Diego Jacobs School of Engineering
Concentration gradient
Of n and p densities
Leads to diffusion of
N into the p-region, and
P into the n-type region.
This leaves behind positive
Donor ion in N-region
And Negative Donor ion
In P-region
Process steps when
Sufficiently large
Potential gradient develops
4
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Equilbrium potential develops across
the p-n junction
UC San Diego Jacobs School of Engineering
Key: e and p now
require a minimum
amount of energy
to cross the
Junction!
Q: How to get
This energy?
5
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Now connect p and n regions via external circuit
UC San Diego Jacobs School of Engineering
6
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Adding to natural bias (i.e. “Reverse” bias)
widens depletion zone
UC San Diego Jacobs School of Engineering
7
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Adding to natural bias (i.e. “Reverse” bias)
widens depletion zone
UC San Diego Jacobs School of Engineering
8
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Current-voltage response for reverse bias
UC San Diego Jacobs School of Engineering
9
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Canceling out natural bias (i.e. “Forward Bias”)
Causes current to flow!
UC San Diego Jacobs School of Engineering
Forward bias reduces width of depletion zone &
“injects” minority carriers (i.e. holes in N-region,
Electrons in P-region) which can then diffuse thru that zone
10
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Current-voltage response forward bias
UC San Diego Jacobs School of Engineering
When forward bias voltage reaches or exceeds the
Natural bias of the p-n junction, large current can
Begin to flow
11
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Diode current-voltage characteristics
UC San Diego Jacobs School of Engineering
12
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