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Organic Light Emitting Diodes
1
What is OLED?
A organic light emitting diode(OLED) is a display
having a flat light emitting technology is made by
placing a series of organic thin films between two
conductors.
They are extremely thin, lightweight and energy-
efficient.
When electricity is passed, light is emitted from
organic layer.
The main importance of OLED is that it is
decomposable after use.
Well, What is the Symbol of OLED?
OLEDs are same symbol as of LEDs.
3
But How OLED operates?
OLEDs have a simple structure. They consist of organic
semiconductor molecules deposited on a substrate of glass
or flexible film between conducting electrodes. When a
current flows between the electrodes, pairs of electrons and
holes are formed, which generates excitons. They return
from the excited state to the ground state by emitting light.
The molecular structure of the semiconductors used
determines the colour of the emitted light. An OLED stack
consists of different layers of OLED materials; each OLED
material layer has its own characteristic function.
4
But what is the applications of this OLED?
5
1. Definition
2. Symbol
3. Working Principle
4. Application
Varactor Diode or Varicap Diode
Well, what are the meaning of the words ‘Varactor’ and ‘Varicap’?
Varactor or Varicap = Variable capacitor
i.e.
The diode whose internal capacitance varies with the variation of the
reverse voltage such type of diode is known as the Varactor diode. It is
used for storing the charge. The varactor diode always works in reverse
bias, and it is a voltage-dependent semiconductor device.
The Varactor diode is used for storing the charge not for flowing the
charge.
What is Varactor Diode?
7
Hey, what is the symbol of Varactor
Diode?
This pic is taken from circuitglobe
8
OR
9
Working Principle of Varactor Diode
The Varactor diode is made up of n-type
and p-type semiconductor material.
The varactor diode operates only in
reverse bias. Because of reverse bias, the
current does not flow. It creates a
depletion region. The depletion region
does not allow the ions to move from one
place to another. This region acts as a
capacitor.
10
Why reverse bias of Varactor diode is very
much relatable to variable capacitor?
Whenever voltage is applied in a reverse bias, it creates a depletion region
through which a current cannot pass. This is quiet relatable to a capacitor
where the dielectric constant is acting as a region through which the current
can not pass. As the voltage increases, we can find that the depletion region
in the varactor diode also increases which means that it will decrease the
capacitance of the diode. The same thing happens when the distance of the
dielectric constant increases. This can be mathematically expressed by:-
where ε – Permittivity of the semiconductor material.
A – area of PN-junction W – width of depletion region
11
Applications of Varactor Diodes
Voltage
controlled
oscillators, VCOs
RF filters
Frequency &
phase
modulators.
Light emitting diode (LED)
symbol
The symbol of LED is similar to the normal p-n junction
diode except that it contains arrows pointing away from
the diode indicating that light is being emitted by the
diode.
LEDs are available in different colors. The most common
colors of LEDs are orange, yellow, green and red.
The schematic symbol of LED does not represent the
color of light. The schematic symbol is same for all colors
of LEDs. Hence, it is not possible to identify the color of
LED by seeing its symbol.
13
LED OPERATIONA light-emitting diode is a two-lead semiconductor light source. It
is a p–n junction diode that emits light when activated. When a
suitable voltage is applied to the leads, electrons are able to
recombine with electron holes within the device, releasing energy
in the form of photons. This effect is called electroluminescence,
and the color of the light (corresponding to the energy of the
photon) is determined by the energy band gap of the
semiconductor.
Different wavelengths involved in the process
determine the different colors produced from the
LEDs. Hence, light emitted by the device depends
on the type of semiconductor material used.
Infrared light is produced by using Gallium Arsenide
(GaAs) as a semiconductor. Red or yellow light is
produced by using Gallium-Arsenide-Phosphorus
(GaAsP) as a semiconductor. Red or green light is
produced by using Gallium-Phosphorus (GaP) as a
semiconductor.
APPLICATION
TUNNEL DIODE
*Symbol of tunnel diode*
A Tunnel diode is a heavily doped p-n junction diode in which the electric current
decreases as the voltage increases.
In tunnel diode, electric current is caused by “Tunneling”. The tunnel diode is used as a very
fast switching device in computers. It is also used in high-frequency oscillators and
amplifiers.
The circuit symbol of tunnel diode is shown
in the below figure. In tunnel diode, the p-
type semiconductor act as an anode and
the n-type semiconductor act as a cathode
*OPERATION OF TUNNEL DIODE - In tunnel diode, the valence
band and conduction band energy levels in the n-type semiconductor are
lower than the valence band and conduction band energy levels in the p-
type semiconductor. Unlike the ordinary p-n junction diode, the difference
in energy levels is very high in tunnel diode. Because of this high
difference in energy levels, the conduction band of the n-type material
overlaps with the valence band of the p-type material.
Quantum mechanics says that the electrons will directly penetrate through
the depletion layer or barrier if the depletion width is very small.
The depletion layer of tunnel diode is very small. It is in nanometers. So the
electrons can directly tunnel across the small depletion region from n-side
conduction band into the p-side valence band.
In ordinary diodes, current is produced when the applied voltage is greater
than the built-in voltage of the depletion region. But in tunnel diodes, a small
voltage which is less than the built-in voltage of depletion region is enough
to produce electric current.
In tunnel diodes, the electrons need not overcome the opposing force from
the depletion layer to produce electric current. The electrons can directly
tunnel from the conduction band of n-region into the valence band of p-
region. Thus, electric current is produced in tunnel diode.
APPLICATION OF
TUNNEL DIODE
 Tunnel diodes are used as logic memory storage
devices.
 Tunnel diodes are used in relaxation oscillator
circuits.
 Tunnel diode is used as an ultra high-speed
switch.
 Tunnel diodes are used in FM receivers.
PHOTODIODE
A photodiode is a semiconductor device that
converts light into an electrical current. The
current is generated when photons are
absorbed in the photodiode. Photodiodes may
contain optical filters, built-in lenses, and may
have large or small surface areas.
SYMBOL OF
PHOTODIODE
They have two terminals coming from the end. The smaller
end of the diode is the cathode terminal, while the
longer end of the diode is the anode terminal.
⚫ TYPES OF PHOTODIODE
⚫ PN Photodiode
⚫ Schottky Photo Diode
⚫ PIN Photodiode
⚫ Avalanche Photodiode
Working of Photodiode
⚫ The working principle of a photodiode is, when a photon of ample energy strikes the
diode, it makes a couple of an electron-hole. This mechanism is also called as the
inner photoelectric effect. If the absorption arises in the depletion region junction,
then the carriers are removed from the junction by the inbuilt electric field of the
depletion region. Therefore, holes in the region move toward the anode, and
electrons move toward the cathode, and a photocurrent will be generated. The
entire current through the diode is the sum of the absence of light and the
photocurrent. So the absent current must be reduced to maximize the sensitivity of
the device.
V-I Characteristics of Photodiode
WHY ARE THEY USED???
⚫ These diodes are widely used in the applications where the
detection of the presence of light, color, position, intensity is
required. The main features of these diodes include the following.
⚫ The linearity of the diode is good with respect to incident light
⚫ Noise is low.
⚫ The response is wide spectral
⚫ Rugged mechanically
⚫ Light weight and compact
⚫ Long life
Applications of Photodiode
⚫ These diodes are used in consumer electronics devices like smoke detectors,
compact disc players, and televisions and remote controls in VCRs.
⚫ Photodiodes are frequently used for exact measurement of the intensity of
light in science & industry. Generally, they have an enhanced, more linear
response than photoconductors.
⚫ These diodes are much faster & more complex than normal PN junction
diodes and hence are frequently used for lighting regulation and in optical
communications.
⚫ In other consumer devices like clock radios, camera light meters, and street
lights, photoconductors are more frequently used rather than photodiodes.
26
27
THANKS
28

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Diodes // LED // OLED

  • 2. What is OLED? A organic light emitting diode(OLED) is a display having a flat light emitting technology is made by placing a series of organic thin films between two conductors. They are extremely thin, lightweight and energy- efficient. When electricity is passed, light is emitted from organic layer. The main importance of OLED is that it is decomposable after use.
  • 3. Well, What is the Symbol of OLED? OLEDs are same symbol as of LEDs. 3
  • 4. But How OLED operates? OLEDs have a simple structure. They consist of organic semiconductor molecules deposited on a substrate of glass or flexible film between conducting electrodes. When a current flows between the electrodes, pairs of electrons and holes are formed, which generates excitons. They return from the excited state to the ground state by emitting light. The molecular structure of the semiconductors used determines the colour of the emitted light. An OLED stack consists of different layers of OLED materials; each OLED material layer has its own characteristic function. 4
  • 5. But what is the applications of this OLED? 5
  • 6. 1. Definition 2. Symbol 3. Working Principle 4. Application Varactor Diode or Varicap Diode
  • 7. Well, what are the meaning of the words ‘Varactor’ and ‘Varicap’? Varactor or Varicap = Variable capacitor i.e. The diode whose internal capacitance varies with the variation of the reverse voltage such type of diode is known as the Varactor diode. It is used for storing the charge. The varactor diode always works in reverse bias, and it is a voltage-dependent semiconductor device. The Varactor diode is used for storing the charge not for flowing the charge. What is Varactor Diode? 7
  • 8. Hey, what is the symbol of Varactor Diode? This pic is taken from circuitglobe 8 OR
  • 9. 9 Working Principle of Varactor Diode The Varactor diode is made up of n-type and p-type semiconductor material. The varactor diode operates only in reverse bias. Because of reverse bias, the current does not flow. It creates a depletion region. The depletion region does not allow the ions to move from one place to another. This region acts as a capacitor.
  • 10. 10 Why reverse bias of Varactor diode is very much relatable to variable capacitor? Whenever voltage is applied in a reverse bias, it creates a depletion region through which a current cannot pass. This is quiet relatable to a capacitor where the dielectric constant is acting as a region through which the current can not pass. As the voltage increases, we can find that the depletion region in the varactor diode also increases which means that it will decrease the capacitance of the diode. The same thing happens when the distance of the dielectric constant increases. This can be mathematically expressed by:- where ε – Permittivity of the semiconductor material. A – area of PN-junction W – width of depletion region
  • 11. 11 Applications of Varactor Diodes Voltage controlled oscillators, VCOs RF filters Frequency & phase modulators.
  • 12. Light emitting diode (LED) symbol The symbol of LED is similar to the normal p-n junction diode except that it contains arrows pointing away from the diode indicating that light is being emitted by the diode. LEDs are available in different colors. The most common colors of LEDs are orange, yellow, green and red. The schematic symbol of LED does not represent the color of light. The schematic symbol is same for all colors of LEDs. Hence, it is not possible to identify the color of LED by seeing its symbol.
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  • 15. LED OPERATIONA light-emitting diode is a two-lead semiconductor light source. It is a p–n junction diode that emits light when activated. When a suitable voltage is applied to the leads, electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. This effect is called electroluminescence, and the color of the light (corresponding to the energy of the photon) is determined by the energy band gap of the semiconductor. Different wavelengths involved in the process determine the different colors produced from the LEDs. Hence, light emitted by the device depends on the type of semiconductor material used. Infrared light is produced by using Gallium Arsenide (GaAs) as a semiconductor. Red or yellow light is produced by using Gallium-Arsenide-Phosphorus (GaAsP) as a semiconductor. Red or green light is produced by using Gallium-Phosphorus (GaP) as a semiconductor.
  • 17. TUNNEL DIODE *Symbol of tunnel diode* A Tunnel diode is a heavily doped p-n junction diode in which the electric current decreases as the voltage increases. In tunnel diode, electric current is caused by “Tunneling”. The tunnel diode is used as a very fast switching device in computers. It is also used in high-frequency oscillators and amplifiers. The circuit symbol of tunnel diode is shown in the below figure. In tunnel diode, the p- type semiconductor act as an anode and the n-type semiconductor act as a cathode
  • 18. *OPERATION OF TUNNEL DIODE - In tunnel diode, the valence band and conduction band energy levels in the n-type semiconductor are lower than the valence band and conduction band energy levels in the p- type semiconductor. Unlike the ordinary p-n junction diode, the difference in energy levels is very high in tunnel diode. Because of this high difference in energy levels, the conduction band of the n-type material overlaps with the valence band of the p-type material. Quantum mechanics says that the electrons will directly penetrate through the depletion layer or barrier if the depletion width is very small. The depletion layer of tunnel diode is very small. It is in nanometers. So the electrons can directly tunnel across the small depletion region from n-side conduction band into the p-side valence band. In ordinary diodes, current is produced when the applied voltage is greater than the built-in voltage of the depletion region. But in tunnel diodes, a small voltage which is less than the built-in voltage of depletion region is enough to produce electric current. In tunnel diodes, the electrons need not overcome the opposing force from the depletion layer to produce electric current. The electrons can directly tunnel from the conduction band of n-region into the valence band of p- region. Thus, electric current is produced in tunnel diode.
  • 19. APPLICATION OF TUNNEL DIODE  Tunnel diodes are used as logic memory storage devices.  Tunnel diodes are used in relaxation oscillator circuits.  Tunnel diode is used as an ultra high-speed switch.  Tunnel diodes are used in FM receivers.
  • 20. PHOTODIODE A photodiode is a semiconductor device that converts light into an electrical current. The current is generated when photons are absorbed in the photodiode. Photodiodes may contain optical filters, built-in lenses, and may have large or small surface areas.
  • 21. SYMBOL OF PHOTODIODE They have two terminals coming from the end. The smaller end of the diode is the cathode terminal, while the longer end of the diode is the anode terminal. ⚫ TYPES OF PHOTODIODE ⚫ PN Photodiode ⚫ Schottky Photo Diode ⚫ PIN Photodiode ⚫ Avalanche Photodiode
  • 22. Working of Photodiode ⚫ The working principle of a photodiode is, when a photon of ample energy strikes the diode, it makes a couple of an electron-hole. This mechanism is also called as the inner photoelectric effect. If the absorption arises in the depletion region junction, then the carriers are removed from the junction by the inbuilt electric field of the depletion region. Therefore, holes in the region move toward the anode, and electrons move toward the cathode, and a photocurrent will be generated. The entire current through the diode is the sum of the absence of light and the photocurrent. So the absent current must be reduced to maximize the sensitivity of the device.
  • 24. WHY ARE THEY USED??? ⚫ These diodes are widely used in the applications where the detection of the presence of light, color, position, intensity is required. The main features of these diodes include the following. ⚫ The linearity of the diode is good with respect to incident light ⚫ Noise is low. ⚫ The response is wide spectral ⚫ Rugged mechanically ⚫ Light weight and compact ⚫ Long life
  • 25. Applications of Photodiode ⚫ These diodes are used in consumer electronics devices like smoke detectors, compact disc players, and televisions and remote controls in VCRs. ⚫ Photodiodes are frequently used for exact measurement of the intensity of light in science & industry. Generally, they have an enhanced, more linear response than photoconductors. ⚫ These diodes are much faster & more complex than normal PN junction diodes and hence are frequently used for lighting regulation and in optical communications. ⚫ In other consumer devices like clock radios, camera light meters, and street lights, photoconductors are more frequently used rather than photodiodes.
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