Camellia Institute of

Technology

Name : Biswajit Kuila

Subject : Analog Electronics

PC-EE 302 (CA-1)

Topic : PN Junction

Sem- 3rd, Year - 2nd

 DIODE
 The name diode is derived from "di-ode" which means a device
that has two electrodes.
 A diode is defined as a two-terminal electronic component that
only conducts current in one direction (so long as it is operated
within a specified voltage level). An ideal diode will have zero
resistance in one direction, and infinite resistance in the
reverse direction.
 Semiconductor diodes are the most common type of diode.
These diodes begin conducting electricity only if a certain
threshold voltage is present in the forward direction (i.e. the
"low resistance" direction).
DIODE

 The basic symbol of p-n junction diode under forward bias and
reverse bias is shown in the below figure
PN Junction Diode

 PN junction diode is one of the fundamental elements in

electronics.
 In this type of diode, we dope one side of a semiconductor
piece with an acceptor impurity and another side with a donor
impurity.
 In ideal conditions, this PN junction behaves as a short circuit
when it is forward biased, and as an open circuit when it is in
the reverse biased.
PN Junction Diode

 In n-type semiconductors, free electrons are the majority

charge carriers whereas in p-type semiconductors, holes are the
majority charge carriers.
 When the n-type semiconductor is joined with the p-type
semiconductor, a p-n junction is formed.
 The p-n junction, which is formed when the p-type and n-type
semiconductors are joined, is called as p-n junction diode.
BIASING OF P-N JUNCTION
SEMICONDUCTOR DIODE
 The process of applying the external voltage to a p-n junction
semiconductor diode is called biasing.
 External voltage to the p-n junction diode is applied in any of
the two methods:
• forward biasing
• reverse biasing.
FORWARD BIASING OF P-N JUNCTION:

 If the p-n junction diode is forward biased, it allows the

electric current flow. Under forward biased condition, the p-
type semiconductor is connected to the positive terminal of
battery whereas; the n-type semiconductor is connected to the
negative terminal of battery.
REVERSE BIASING OF P-N JUNCTION:

 If the p-n junction diode is reverse biased, it blocks the electric

current flow. Under reverse biased condition, the p-type
semiconductor is connected to the negative terminal of battery
whereas; the n-type semiconductor is connected to the positive
terminal of battery.
SILICON SEMICONDUCTOR DIODES:

• For designing the diodes, silicon is more preferred over

germanium.
• The p-n junction diodes made from silicon semiconductors works
at high temperature than the germanium semiconductor diodes.
• Forward bias voltage for silicon semiconductor diode is
approximately 0.7 volts whereas for germanium semiconductor
diode is approximately 0.3 volts.
• Silicon semiconductor diodes do not allow the electric current
flow, if the voltage applied on the silicon diode is less than 0.7
volts.
• Silicon semiconductor diodes start allowing the current flow, if
the voltage applied on the diode reaches 0.7 volts.
GERMENIUM SEMICONDUCTOR DIODES:

• Germanium semiconductor diodes do not allow the electric

current flow, if the voltage applied on the germanium diode is less
than 0.3 volts.
• Germanium semiconductor diodes start allowing the current
flow, if the voltage applied on the germanium diode reaches 0.3
volts.
• The cost of silicon semiconductors is low when compared with
the germanium semiconductors.
 V-I Characteristics of PN Junction
Diode
 The V-I characteristics of the PN junction diode is a voltage Vs current
graph, that explains the relationship between voltage and current in a
Diode.
 When the PN junction diode is in forward bias, at zero voltage, zero
current will flow through the diode. If the applied voltage is less than the
barrier potential, a small current flows through the diode. But, when the
applied voltage exceeds the barrier potential, the current starts flowing
through the diode and increases rapidly. This applied voltage value that
will start the current flow through the diode is known as forward voltage
or VF of a diode. It is also called knee voltage.
 When the PN junction diode is in reverse bias, at the zero reverse voltage
no current flows through it. If the reverse voltage increases a very small
current starts flowing through the diode, that known as Reverse Leakage
Current. This reverse current is so small, its range of 0.000000001A or
1nA, that’s has no notable effects in a circuit, and it is considered almost
zero.
V-I Characteristics of PN Junction
Diode
 After a certain point when you
further increase the reverse
voltage, the diode starts
conducting heavily in the
reverse direction and the current
starts flowing rapidly through
the diode. This process
called Avalanche
Breakdown and this voltage is
known as Reverse breakdown
voltage.
APPLICATIONSOF P-N JUNCTION DIODE

• P-N junction diode can be used as a photodiode as the diode is

sensitive to the light when the configuration of the diode is
reverse-biased.
• It can be used as a solar cell.
• When the diode is forward-biased, it can be used in LED lighting
applications.
• It is used as rectifier in many electric circuits and as a voltage-
controlled oscillator in varactors.
SUMMARY OF P-N JUNCTION DIODE

• Semiconductors contain two types of mobile charge carriers, "Holes"

and "Electrons".
• The holes are positively charged while the electrons negatively
charged.
• A semiconductor may be doped with donor impurities such as Antimony
(N- type doping), so that it contains mobile charges which are primarily
electrons.
• A semiconductor may be doped with acceptor impurities such as Boron
(P- type doping), so that it contains mobile charges which are mainly
holes.
• The junction region itself has no charge carriers and is known as the
depletion region.
SUMMARY OF P-N JUNCTION DIODE

• The junction (depletion) region has a physical thickness that

varies with the applied voltage.
• When a diode is Zero Biased no external energy source is applied
and a natural Potential Barrier is developed across a depletion
layer which is approximately 0.5 to 0.7v for silicon diodes and
approximately 0.3 of a volt for germanium diodes.
• When a junction diode is Forward Biased the thickness of the
depletion region reduces and the diode acts like a short circuit
allowing full circuit current to flow.
SUMMARY OF P-N JUNCTION DIODE

• When a junction diode is Reverse Biased the thickness of the

depletion region increases and the diode acts like an open circuit
blocking any current flow, (only a very small leakage current will
flow).
Thank You