PPT: P-N Junction & Diodes

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P-N Junction Diode
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P-N Junction Diode
Intrinsic Semiconductor- 
The electrical characteristics of intrinsic semiconductor (Si or Ge) can be 
improved by adding impurity in a process called doping. 
External (doped) Semiconductor- 
N-type Semiconductor - Semiconductor doped with Pentavalent material (P, As, 
Sb etc.) contains an excess of free electrons. 
P-type Semiconductor - Semiconductor doped with Trivalent material (Al, Ga 
etc.) contains an excess of holes.
P-N junction diode-
One end of a semiconductor bar (Si or Ge) crystal is doped as a p-type material 
and the other end as a n-type material.
Biasing of  P-N junction diode-
Unbiased - No external voltage is applied.
Forward Biased- P-terminal of diode connected to positive terminal and N-
terminal of diode connected to negative terminal of the battery.
Reverse Biased - P-terminal of diode connected to negative terminal and N-
terminal of diode connected to positive terminal of the battery.
P-N Junction Diode: Introduction
Block Diagram
P-N Junction diode
Circuit Symbol
Reverse Biased
Forward Biased
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P-N Junction Diode
Intrinsic Semiconductor- 
The electrical characteristics of intrinsic semiconductor (Si or Ge) can be 
improved by adding impurity in a process called doping. 
External (doped) Semiconductor- 
N-type Semiconductor - Semiconductor doped with Pentavalent material (P, As, 
Sb etc.) contains an excess of free electrons. 
P-type Semiconductor - Semiconductor doped with Trivalent material (Al, Ga 
etc.) contains an excess of holes.
P-N junction diode-
One end of a semiconductor bar (Si or Ge) crystal is doped as a p-type material 
and the other end as a n-type material.
Biasing of  P-N junction diode-
Unbiased - No external voltage is applied.
Forward Biased- P-terminal of diode connected to positive terminal and N-
terminal of diode connected to negative terminal of the battery.
Reverse Biased - P-terminal of diode connected to negative terminal and N-
terminal of diode connected to positive terminal of the battery.
P-N Junction Diode: Introduction
Block Diagram
P-N Junction diode
Circuit Symbol
Reverse Biased
Forward Biased
Unbiased P-N Junction Diode
As soon as junction is formed, the electrons in the N-type 
material diffuse across the junction to the P-type material 
and the holes in the P-type material diffuse across the 
junction to the N-type material. In this process they 
recombine each other. 
After a few recombination of electrons and holes, there is 
depletion of mobile charge carriers in the region near the 
junction on the both sides. Such region is known as 
depletion or space charge region.
Width of depletion region  is inversely proportional to 
doping level and is directly proportional to reverse bias.
Due to presence of opposite immobile impurity ions on both 
sides of the junction, a potential is developed which stopped 
further diffusion of electrons and holes. Such potential is 
known as barrier potential or built in potential. Barrier 
potential for Ge is 0.3 V and that for Si is 0.7 V .
Formation of a depletion  region 
around the junction.
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P-N Junction Diode
Intrinsic Semiconductor- 
The electrical characteristics of intrinsic semiconductor (Si or Ge) can be 
improved by adding impurity in a process called doping. 
External (doped) Semiconductor- 
N-type Semiconductor - Semiconductor doped with Pentavalent material (P, As, 
Sb etc.) contains an excess of free electrons. 
P-type Semiconductor - Semiconductor doped with Trivalent material (Al, Ga 
etc.) contains an excess of holes.
P-N junction diode-
One end of a semiconductor bar (Si or Ge) crystal is doped as a p-type material 
and the other end as a n-type material.
Biasing of  P-N junction diode-
Unbiased - No external voltage is applied.
Forward Biased- P-terminal of diode connected to positive terminal and N-
terminal of diode connected to negative terminal of the battery.
Reverse Biased - P-terminal of diode connected to negative terminal and N-
terminal of diode connected to positive terminal of the battery.
P-N Junction Diode: Introduction
Block Diagram
P-N Junction diode
Circuit Symbol
Reverse Biased
Forward Biased
Unbiased P-N Junction Diode
As soon as junction is formed, the electrons in the N-type 
material diffuse across the junction to the P-type material 
and the holes in the P-type material diffuse across the 
junction to the N-type material. In this process they 
recombine each other. 
After a few recombination of electrons and holes, there is 
depletion of mobile charge carriers in the region near the 
junction on the both sides. Such region is known as 
depletion or space charge region.
Width of depletion region  is inversely proportional to 
doping level and is directly proportional to reverse bias.
Due to presence of opposite immobile impurity ions on both 
sides of the junction, a potential is developed which stopped 
further diffusion of electrons and holes. Such potential is 
known as barrier potential or built in potential. Barrier 
potential for Ge is 0.3 V and that for Si is 0.7 V .
Formation of a depletion  region 
around the junction.
Forward biased P-N Junction Diode
In this case, two types of electric fields exit within the 
diode- External electric field across the diode terminals 
due to external bias voltage and Internal electric field 
across depletion region due to barrier potential.
Due to external electric field, holes in P type 
semiconductor region are repelled from the positive 
terminal and electrons in N type semiconductor region 
are repelled from the negative terminal of the source. 
Therefore width of depletion region is reduced compared 
to unbiased P-N junction diode.
The decreased barrier potential is helpful to the 
majority carriers in crossing the junction. Hence more 
majority carriers drift across the junction which results 
a current in forward biased diode. Such current is 
known as forward current and it is order of milli-ampere. 
The forward current increases with increasing the 
forward bias voltage.
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P-N Junction Diode
Intrinsic Semiconductor- 
The electrical characteristics of intrinsic semiconductor (Si or Ge) can be 
improved by adding impurity in a process called doping. 
External (doped) Semiconductor- 
N-type Semiconductor - Semiconductor doped with Pentavalent material (P, As, 
Sb etc.) contains an excess of free electrons. 
P-type Semiconductor - Semiconductor doped with Trivalent material (Al, Ga 
etc.) contains an excess of holes.
P-N junction diode-
One end of a semiconductor bar (Si or Ge) crystal is doped as a p-type material 
and the other end as a n-type material.
Biasing of  P-N junction diode-
Unbiased - No external voltage is applied.
Forward Biased- P-terminal of diode connected to positive terminal and N-
terminal of diode connected to negative terminal of the battery.
Reverse Biased - P-terminal of diode connected to negative terminal and N-
terminal of diode connected to positive terminal of the battery.
P-N Junction Diode: Introduction
Block Diagram
P-N Junction diode
Circuit Symbol
Reverse Biased
Forward Biased
Unbiased P-N Junction Diode
As soon as junction is formed, the electrons in the N-type 
material diffuse across the junction to the P-type material 
and the holes in the P-type material diffuse across the 
junction to the N-type material. In this process they 
recombine each other. 
After a few recombination of electrons and holes, there is 
depletion of mobile charge carriers in the region near the 
junction on the both sides. Such region is known as 
depletion or space charge region.
Width of depletion region  is inversely proportional to 
doping level and is directly proportional to reverse bias.
Due to presence of opposite immobile impurity ions on both 
sides of the junction, a potential is developed which stopped 
further diffusion of electrons and holes. Such potential is 
known as barrier potential or built in potential. Barrier 
potential for Ge is 0.3 V and that for Si is 0.7 V .
Formation of a depletion  region 
around the junction.
Forward biased P-N Junction Diode
In this case, two types of electric fields exit within the 
diode- External electric field across the diode terminals 
due to external bias voltage and Internal electric field 
across depletion region due to barrier potential.
Due to external electric field, holes in P type 
semiconductor region are repelled from the positive 
terminal and electrons in N type semiconductor region 
are repelled from the negative terminal of the source. 
Therefore width of depletion region is reduced compared 
to unbiased P-N junction diode.
The decreased barrier potential is helpful to the 
majority carriers in crossing the junction. Hence more 
majority carriers drift across the junction which results 
a current in forward biased diode. Such current is 
known as forward current and it is order of milli-ampere. 
The forward current increases with increasing the 
forward bias voltage.
Reverse biased P-N Junction Diode
Due to external electric field, holes in P type semiconductor region are attracted toward the 
negative terminal and electrons in N type semiconductor region are attracted toward the 
positive terminal of the source. Therefore depletion region becomes wider compared to 
unbiased P-N junction diode.
The increased barrier potential is helpful to the minority carriers in crossing the junction. 
Hence a current flows due to minority carries in reverse biased P-N junction diode. Such 
current is known as reverse saturation current. The reverse saturation current  is order of 
nano-ampere in case of Si and micro-ampere in case of Ge.
If the reverse bias voltage is made too high, the current through P-N junction diode 
increases abruptly. This phenomenon is known as breakdown of the diode and the voltage at 
which it occurs is known as breakdown voltage. There are two types of mechanism of 
breakdown- Avalanche breakdown and Zener breakdown.