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Chapter 1
Part 2
p-n Junction
Chapter 1, Part 2, p-n Junction
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Objectives:
¾Discuss zero biasing of a p-n junction
In this Part I, we will:
Determine the properties of a p-n junction
Chapter 1, Part 2, p-n Junction
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p-n junction
When p-type material and n-type material are “joined” the electrons and
holes in the region of the junction will combine, resulting in a lack of
carriers in the region near the junction.
n-type
p-type
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Depletion region
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Electron diffusion
Hole diffusion
This region is called
Depletion region due
to the depletion of
Chapter 1, Part 2, p-n Junction
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carriers in this region
Semiconductor single crystal (wafer)
doping
doping
n-type
p-type
Forming of p-n Junction
Metallurgical junction
The flow of holes from the p-
region uncovers negatively
charged acceptor ions, and
the flow of electrons from the
Built-in Potential Barrier or
n-region uncovers positively
charged donor ions.
An electric field oriented in
the direction from the (+)
charge to the (-) charge will be
created.
Built-in Voltage (Vbi) is a
potential difference across
the depletion region
Chapter 1, Part 2, p-n Junction
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Built-in Potential Barrier or Built-in Voltage (Vbi)
VT: Thermal voltage
k: Boltzman’s constant
T: absolute temperature(K)
e: electronic charge
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ln
ln
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kT
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Example: Calculate the Vbi of a p-n junction.
Consider a silicon p-n junction at T=300K, doped at
Na = 1016cm-3 in the p-region and Nd=1017cm-3 in the n-region.
Na: acceptor concentration
Nd: donor concentration
VT =kT/e; VT =0.026V at 300K
Here, ni =