Schottky barrier diode Zener diode Varactor diode Tunnel diode Gallium Arsenide device LASER diode LDR

1. UNIT 4
SPECIAL
SEMICONDUCTOR
DEVICES
Dr.S.Muthumanickam, BE., ME., Ph.D.,
Associate Professor
Department of Electronics and Communication
Engineering
DATE: 9.06.2021

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3. TOPICS
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 Schottky barrier diode
 Zener diode
 Varactor diode
 Tunnel diode
 Gallium Arsenide device
 LASER diode
 LDR

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SCHOTTKY BARRIER
DIODE

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Molybdenum
Palladium.
Platinum.
Chromium
The Ohmic contact is also a metal-
semiconductor junction when the N-
region of the junction is highly doped
the junction does not acts as the
rectifier and becomes the Ohmic which
enables the current flow in either
direction just like the conductor.

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Applications of the
Schottky Diode:
Due to the fast response of the
Schottky diode it finds
application in high speed
circuits.
• AC to DC converter.
• High current power
supplies.
• In mixers.
• In radar systems.
• voltage clamper circuits.

7. ZENER DIODE
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9. ZENER DIODE
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 A zener diode is a heavily doped p-n junction
semiconductor device designed to operate in the
reverse breakdown region.
 The breakdown voltage of a zener diode is
carefully set by controlling the doping level
during manufacture.
 The name zener diode was named after the
American physicist Clarance Melvin Zener who
discovered the zener effect.
 Zener diodes are mainly used to protect
electronic circuits from over voltage.

10. Avalanche Breakdown
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 When high reverse voltage is applied to the p-n
junction diode, the free electrons (minority
carriers) gains large amount of energy and
accelerated to greater velocities.
 The free electrons moving at high speed will
collides with the atoms and knock off more
electrons.
 These electrons are again accelerated and
collide with other atoms. Because of this
continuous collision with the atoms, a large
number of free electrons are generated.
 As a result, electric current in the diode
increases rapidly. This sudden increase in
electric current may permanently destroys the
normal diode.
 However, avalanche diodes may not be
destroyed because they are carefully designed
to operate in avalanche breakdown region.
 Avalanche breakdown occurs in zener diodes
with zener voltage (Vz) greater than 6V.

11. ZENER BREAKDOWN
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 The zener breakdown occurs in heavily
doped p-n junction diodes because of their
narrow depletion region.
 When reverse biased voltage applied to the
diode is increased, the narrow depletion
region generates strong electric field.
 The valance electrons which break bonding
with parent atom will become free electrons.
 This free electrons carry electric current from
one place to another place.
 At zener breakdown region, a small increase
in voltage will rapidly increases the electric
current.

12. ZENER DIODE…points to remember
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 Zener breakdown occurs at low reverse voltage
whereas avalanche breakdown occurs at high reverse
voltage.
 Zener breakdown occurs in zener diodes because
they have very thin depletion region.
 Breakdown region is the normal operating region for
a zener diode.
 Zener breakdown occurs in zener diodes with zener
voltage (Vz) less than 6V.

13. VI CHARACTERISTICS
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16. ZENER DIODE
⬢
Advantages of zener diode
 Power dissipation capacity
is very high
 High accuracy
 Small size
 Low cost
⬢
Applications of zener diode
 It is normally used as voltage reference
 Zener diodes are used in voltage
stabilizers or shunt regulators.
 Zener diodes are used in switching
operations
 Zener diodes are used in clipping and
clamping circuits.
 Zener diodes are used in various
protection circuits 16

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ZENER Diode
as
Voltage Regulator
Provides a stable power supply to drive
the circuits

18. ZENER Diode as Voltage Regulator
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Find out the Zener parameters
IL, Is, Iz, Vth, Pz

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POWER

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29. Find out the Min and Max Value of
RL, Rs and Vs
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50. VARACTOR DIODE
VARICAP
VARIABLE REACTANCE
VARIABLE CAPACITANCE
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These varactor diodes are advantageous
compact in size, economical, reliable and less prone to noise
when compared to other diodes.
Applications
1.Tuning circuits to replace the old style variable capacitor
tuning of FM radio
2. Small remote control circuits
3.Tank circuits of receiver or transmitter for auto-tuning as
case of TV
4.Signal modulation and demodulation.
5.Microwave frequency multipliers as a component of LC
resonant circuit
6.Very low noise microwave parametric amplifiers
7.AFC circuits
8.Adjusting bridge circuits
9.Adjustable bandpass filters
10.Voltage Controlled Oscillators (VCOs)
11.RF phase shifters
12.Frequency multipliers

55. TUNNEL DIODE
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57.  The tunnel diode is a heavily doped PN-
junction diode.
 The concentration of impurity in the norma
PN-junction diode is about 1 part in 10^8
and in the tunnel diode, the concentration o
the impurity is about 1 part in 10^3.
 Because of the heavy doping, the diode
conducts current both in the forward as wel
as in the reverse direction.
 It is a fast switching device; thereby it is
used in high-frequency oscillators,
computers and amplifiers.
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Construction of
Tunnel Diode
• The device is constructed by
using the two terminals namely
anode and cathode.
• The p-type semiconductor acts
as an anode, and the n-type
semiconductor material acts as a
cathode.
• The gallium arsenide,
germanium and gallium
antimonide are used for
manufacturing the tunnel diode.

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60. Volt-Amp Characteristic
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Tunnel diode

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Advantages & Disadvantages of Tunnel Diode
 The tunnel diode has low cost.
 It produces low noise, and their fabrication is very simple.
 The diode gives a fast response, and it is moderate in operation.
 The tunnel diode works on low power.
 The disadvantage of the tunnel diode is that output voltage of the
diode swings.
 It is a two terminal device, but their input and output circuits are
not isolated from each other.
Applications of Tunnel Diode
 The tunnel diode can be used as an amplifier and as an oscillator
for detecting small high-frequency or as a switch.
 It is a high-frequency component because it gives the very fast
responses to the inputs.
 The tunnel diode is not widely used because it is a low current
device.

70. GALLIUM ARSENIDE
(GaAs) DEVICES
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Gallium arsenide - electrons race through its
crystalline structure faster than they can
move through silicon.

71. Energy Band Diagram of GaAs device
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Gallium arsenide (GaAs) is a
compound built from the
elements gallium and
arsenic. It is often referred to
as a III-V compound because
gallium and arsenic are in the
III group and V group of the
periodic table, respectively.

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The applications of gallium arsenide are
listed below:
1. Gallium arsenide can be used to manufacture devices such as monolithic
microwave integrated circuits, microwave frequency integrated circuits,
infrared light-emitting diodes, solar cells, laser diodes and optical windows.
2. GaAs have a direct bandgap unlike many other semiconductors implying it
can emit light with high efficiency. Being a direct bandgap material, it is
resistant to radiation damage enabling its use in optical windows and space
electronics in high power applications.
3. It is also used as an electrical substrate and offers natural isolation between
circuits and devices. This makes it suitable for millimeter-wave and
microwave ICs.
4. Solar cells based on GaAs power the Opportunity and Spirit rovers that are
exploring the surface of Mars. A number of solar cars make use of GaAs in
solar arrays.
5. GaAs diodes are used to detect X-rays.

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LASER DIODE SYMBOL
LASER V-I CHARACTERISTICS
L∞ƛ
Construction of

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Applications of Laser Diode
 CD and DVD players
 Barcode scanners
 Cable and High Definition (HD) TV transmission
 Medical applications including surgical instruments and to heal retina and brain.
 Intrusion detection systems
 Remote control applications
 Industrial applications including welding, precision cutting of metals, heat treating, cladding, etc.
 Fibre Optic Communication (using various types of fibre optical cables)
 High speed, Long distance communication
 Spectroscopic sensing
 Range finders
 Laser pointers
 Printing
 Integrated Circuits

77. LASER APPLICATION IN
MEDIA…
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LDR -
Light
Dependent
Resistor

79. LDR Characteristics
Applications:
 The LDR is used in the infrared astronom
 The LDR is used in light failure alarm
circuits and used in light meter.
 The LDR used in smoke detectors.
 It is used for automatic contrast and
brightness control in television receivers.
 It is used in photosensitive relay.
 It is used in optical coding.
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