Type of all_kind_of_diode.zenzer_diode_p-n_junction_diode_pin_diode_led_diode_tunnel_diode_vractor_diode_schottky_diode_photo_diode_avalanche_diode_laser_diode

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City University,Dhaka,Bangladesh
Assignment On,
Types of Diode……
Cource title:Electronic Circuit I
Cource Code: EEE301
Submission date:7-02-2017
Submitted by:
Robioul Awal
ID:153103022
Batch:10th
Facebookb.com/Robioul999

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What is a Diode………..?
A Diode is the simplest two-terminal unilateral semiconductor device. It allows current to
flow only in one direction and blocks the current that flows in the opposite direction. The two
terminals of the diode are called as anode and cathode. The symbol of diode is as shown
in the figure below.
characteristics of a diode:
How Diodes work…?
The diode operates when a voltage signal is applied across its terminals. The application of a DC voltage to
make the diode operate in a circuit is called as ‘Biasing’. As already mentioned above the diode resembles to that
of a one way switch so it can either be in a state of conduction or in a state of non conduction. The ‘ON’ state of a
diode is achieved by ‘Forward biasing’ which means that positive or higher potential is applied to the anode and
negative or lower potential is applied at the cathode of the diode. In other words, the ‘ON’ state of diode has the
applied current in the same direction of the arrow head. The ‘OFF’ state of a diode is achieved by ‘Reverse
biasing’ which means that positive or higher potential is applied to the cathode and negative or lower potential is
applied at the anode of the diode. In other words, the ‘OFF’ state of diode has the applied current in the opposite
direction of the arrow head.
During ‘ON’ state, the practical diode offers a resistance called as the ‘Forward resistance’. The diode requires a
forward bias voltage to switch to the ‘ON’ condition which is called Cut-in-voltage. The diode starts conducting in
reverse biased mode when the reverse bias voltage exceeds its limit which is called as the Breakdown voltage.
The diode remains in ‘OFF’ state when no voltage is applied across it.
A simple p-n juction diode is fabricated by doping p and n type layers on a silicon or germanium
wafer. The germanium and silicon materials are prefered for diode fabrication because:
· They are available in high purity. Slight doping like one atom per ten million atoms of a desired
impurity can change the conductivity to a considerable level. The properties of these materials
change on applying heat and light and hence it is important in the devlopment of heat and light
sensetive devices.

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Types of Diode:
The types of diode are as follow-
1. Zener diode
2. P-N junction diode
3. Tunnel diode
4. Varactor diode
5. Schottky diode
6. Photo diode
7. PIN diode
8. Laser diode
9. Avalanche diode
10.Light emitting diode
1.Zener diodes:
Zener diodes are semiconductor diodes which have been manufactured to have their
reverse breakdown occur at a specific, well-defined voltage (its “Zener voltage”), and
that are designed such that they can be operated continuously in that breakdown
mode. Commonly available Zener diodes are available with breakdown voltages
(“Zener voltages”) anywhere from 1.8 to 200 V.

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The schematic symbol for a Zener diode is shown above– it is very similar to that of
a regular diode, but with bent edges on the bar. The Zener still conducts electricity in
the forward direction like any other diode, but also conducts in the reverse direction,
if the voltage applied is reversed and larger than the Zener breakdown voltage
V-I characteristics:
The V-I Characteristics of a Zener Diode can be divided into two parts:
 Forward Characteristics
 Reverse Characteristics

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Advantages & Disadvantages:
Advantages:
 Control of flowing current
 Size and Expense
 Performance
 Compatibility and Obtainability
Disadvantages:
Zener diodes cancel out voltages by applying even larger voltages in the reverse
direction, wasting electricity in the process. Additionally, Zener diodes have a
relatively poor regulation ratio and are generally not as good as transistors.
2.Tunnel Diode:

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I/V Characteristics:
As forward bias is applied, significant I is produced.
After continuous increase of V, the current achieves its minimum value called as
Valley Current. After further increase in V, current start increasing as ordinary diode.

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Advantage:
1. environmental immunity.
2. Low cost
3. Simplicity
4. Low noise
5. High speed
6. Low power consumption.
Disadvantage:
Only disadvantage of tunnel diode are its low output voltage swing and it is a
two terminal device . hence there is no isolation between input and output . hence
transistor is used along with a tunnel diode for frequencies below 1 GHz.
3.Varactor diode:
Varactor Diode is a reverse biased p-n junction diode, whose
capacitance can be varied electrically. As a result these diodes
are also referred to as varicaps, tuning diodes, voltage variable
capacitor diodes, parametric diodes and variable capacitor diodes.
Characteristics:
1.Low-noise characteristic : produce much less noise than most conventional amplifiers.
2.Low Cost
3.High Realibity
4.Light Weath
5.Small Size

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Advantage:
It is basically an electrically controlled variable capacitor no moving parts need.
a monitored voltage source to hold the value temperature sensitive Si based
Disadvantage:
dont work over 100C variable capacitors in the mechanical adjusted variety work
with higher voltages arent voltage spike sensitive and are far more rugged are in
picofarad to micro farad range can handle many kilowatts set and forget dont need
controls to maintain capacitance arent temperature sensitive can be motor. driven for
electric control.
4. Schottky diode:
Schottky diode: it is also referred to as Schottky barrier diode or as
hot carrier diode. This is a diode with semiconductor-metal junction.
This device can simply rectify frequencies greater than 300 MHz. Its
forward voltage drop is also very low (0.15 to 0.45 V). This results in
higher switching speed and improved system efficiency. The junction in
the diode is formed by the metal (such as gold, tungsten, chromium,
platinum, molybdenum or certain silicides) and N-type doped silicon
semiconductor.
V-I characteristics of Schottky Diode:

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Schottky diode I-V characteristics:
Schottky diode is a metal-semiconductor (MS) diode
Historically, Schottky diodes are the oldest diodes
MS diode electrostatics and the general shape of the MS diode I-V characteristics are similar
to p+n diodes, but the details of current flow are different.
Dominant currents in a p+n diode
arise from recombination in the depletion layer under small forward bias.
arise from hole injection from p+ side under larger forward bias.
Dominant currents in a MS Schottky diodes
Electron injection from the semiconductor to the metal.
Advantages:
Disadvantages…
Limitations: The most evident limitations of Schottky diodes are the relatively low reverse
voltage ratings for silicon-metal Schottky diodes, typically 50 V and below, and a relatively
high reverse leakage current. Some higher-voltage designs are available; 200V is considered
a high reverse voltage.
Reverse leakage current, because it increases with temperature, leads to a thermal
instability issue. This often limits the useful reverse voltage to well below the actual rating.
While higher reverse voltages are achievable, they would be accompanied by higher
forward voltage drops, comparable to other types; such a Schottky diode would have no
advantage.

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5.Photodiode:
 A photodiode is one type of light detector, used to convert the light
into current or voltage based on the mode of operation of the
device.
 It comprises of optical filters, built-in lenses and also surface areas.
 These diodes have a slow response time when the surface area of
the photodiode increases.
 Photodiodes are alike to regular semiconductor diodes
V-I Characteristics of Photodiode:
V-I characteristics: The voltage-current equation for photodiode is given by following equation. P
I = I (eV / ηVT −1) − I
0 (1)
Here I0 : reverse saturation current, V: applied potential to diode, VT: voltage equivalent to
temperature=KT/e, η:constant (=1 for Ge and 2 for Si), IP: photo current. The photocurrent is
product of responsivity of photo diode and power of incident light. i.e. IP=RλP. The ,responsivity of a
photodiode is a measure of the sensitivity to light, and it is defined as the ratio of the photocurrent
IP to the incident light power P at a given wavelength. In the forward biased condition, the current
through diode increases exponentially. But in thereverse biased diode, V is negative hence the
exponential term becomes less than 1 therefore ….the equation becomes as, IR = −I0 – IP

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Using of photo Diode:
 Cameras
 Medical devices
 Safety equipment
 Optical communication devices
 Position sensors
 Bar code scanners
 Automotive devices
 Surveying instruments
Advantages of photodiode
1. can be used as variable resistance device.
2. Highly sensitive to the light.
3. The speed of the operation is very high . the switching of current and hence
the resistance value from high to low or other wise is very fast .
Disadvantages of photodiode
(i) The dark current is temperature dependent .
(ii) The overall photo diode characteristics are temperature dependent Hence
have poor temperature stability.
(iii) The current and change in current is in the range of TA which may not be
sufficient to drive other circuits. Hence amplification is necessary.

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6.Pin diode:
The PIN diode is a one type of photo detector, used to convert optical signal into an
electrical signal. The PIN diode comprises of three regions, namely P-region, I-region and N-
region. Typically, both the P and N regions are heavily doped due to they are utilized for
Ohmic contacts.The intrinsic region in the diode is in contrast to a PN junction diode. This
region makes the PIN diode an lower rectifier, but it makes it appropriate for fast switches,
attenuators, photo detectors and applications of high voltage power electronics.
IV-Characteristics of PIN Diode
The forward series resistance characteristic and the reverse capacitance characteristic
are shown graphically in Below Figure for a .typical pin diode. The pin diode is used as a
dc-controlled microwave switch operated by rapid changes in bias or as a modulating
device that takes advantage of the variable forward-resistance characteristic. Since no
recti�cation occurs at the pn junction, a highfrequency .signal can be modulated (varied)
by a lower-frequency bias variation. A pin diode can also be used in attenuator
applications because its resistance can be controlled by the amount of current. Certain
types of pin diodes are used as photodetectors ,in fiber-optic systems.
Advantages of PIN diode:
High voltage rectfier:

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The PIN diode can be used as a high voltage recti�er. The intrinsic region provides
a greater separation
between the PN and N regions, allowing higher reverse voltages to be tolerated.
RF switch:
The PIN diode makes an ideal RF switch. The intrinsic layer between the P and N
regions increases the distance
between them. This also decreases the capacitance between them, thereby
increasing he level of isolation when the diode is
reverse biased.
Photodetector
: As the conversion of light into current takes place within the depletion region of a
photdiode, increasing the
depletion region by adding the intrinsic layer improves the performance by increasing
he volume in which light conversion
occurs
Disadvantages of PIN diode.
Has a reverse recovery time which contributes to power loss.
7.Avalanche Diode:
An avalanche diode is a special type of semiconductor device designed
to operate in reverse breakdown region. Avalanche diodes are used as
relief valves (a type of valve used to control the pressure in a system) to
protect electrical systems from excess voltages.
How avalanche diode works?
IV-Characteristics of Avalance Diode:

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In electronics, an avalanche diode is a diode (made from silicon or other semiconductor) that is
designed to experience avalanche breakdown at a specified reverse bias voltage.
Current-voltage characteristics of electrical components and circuits can be collected in
two ways:
1. When potentiostatic access to connect to the electrode voltage . Applied voltage
then gradually increase until it reaches the final voltage .
2. In galvanostatic approach set stream , which is then gradually increased to a final
current .
Avalanche photodiode advantages and disadvantages
The avalanche photodiode has a number of different characteristics to the normal p-n or p-i-n
photodiodes, making them more suitable for use in some applications. In view of this it is worth
summarising their advantages and disadvantages..
The main advantages of the avalanche photodiode include:
 Greater level of sensitivity
The disadvantages of the avalanche photodiode include:
 Much higher operating voltage may be required.
 Avalanche photodiode produces a much higher level of noise than a p-n photodiode
 Avalanche process means that the output is not linear

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8.Laser Diode:
A laser diode, also known as an injection laser or diode laser, is
a semiconductor device that produces coherent radiation (in which the
waves are all at the same frequency and phase) in the visible
or infrared (IR) spectrum when current passes through it. Laser diodes are
used in optical fiber systems, compact disc (CD) players, laser printers,
remote-control devices, and intrusion detection systems.
IV-Characteristics of Laser Diode:
The laser diode specification for the forward voltage across the diode is required in a number of
areas of the design. Often laser diode manufacturers prefer to place the voltage on the vertical
axis.
From the diagram it can be seen that the voltage across the laser diode is typically around 1.5
volts, although it is necessary to check for the particular laser diode in question. The forward
voltage specification will vary according to the materials used in the diode, current, etc.
Although the forward voltage does vary with temperature, this is not normally a major
consideration.

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Advantages of Diode Lasers
Compared to most laser types, diode lasers are less expensive and more compact,
making them ideal for small electronic devices, such as CD and DVD players, CD-
ROMs, DVD-ROMs and other optical data storage devices. Laser printers, laser fax
machines and supermarket bar code readers all use diode lasers. Using helium-
neon lasers increases the size of these devices by as much as five times. Diode
lasers use much less power than most types of lasers. While gas and solid-state
lasers require a power supply in kilo-volts, diode lasers typically run on small volt
batteries.
Disadvantages of Diode Lasers
Diode laser beams are highly divergent, meaning "wedge-shaped," instead of
straight and parallel, and have shorter coherent distances, which makes for inferior
quality in optics performance. They are not as well-suited as helium-neon lasers for
high-quality holography. Moreover, semiconductors, in electronic devices, are prone
to static electrical discharges, meaning diode lasers in these gadgets can be
damaged by unstable and fluctuating power supply. Also prone to gradual aging,
diode lasers, over time, use increasing amounts of power with diminishing efficiency.
The lens required for beam correction adds to the diode laser's fragility such that
damage to the lens renders the laser non-functional.
9.Light Emitting Diode (LED):
The holes are present in the valance band and the free electrons are in the
conduction band. When a p-n junction is forward biased, the electron from n-type
semiconductor material cross the p-n junction and combine with the holes in the p-
type semiconductor material. Thus with respect to the holes, the free electrons are at
higher energy level.

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IV-Characteristics of (LED):
For a Light Emitting Diode to emit any form of light it needs a current to flow
through it, as it is a current dependant device. As the LED is to be connected in a
forward bias condition across a power supply it should be current limited using a
series resistor to protect it from excessive current flow. From the graph above we
can see that each LED has its own forward voltage drop across the PN-junction
and this parameter, which is determined by the semiconductor material used, is the
forward voltage drop for a given amount of forward conduction current.
Advantage: > LEDs produce more light per watt than do incandescent bulbs; this is useful in battery
powered or energysaving devices .
Disadvantage: > LED performance largely depends on the ambient temperature of the operating environment.
Driving the LED hard in high ambient temperatures may result in overheating of the LED package, eventually leading to
device failure.

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10.P-N Junction Diode:
A p–n junction is a boundary or interface between two types of semiconductor material, p-
type and n-type, inside a single crystal of semiconductor. The "p" (positive) side contains an
excess of holes, while the "n" (negative) side contains an excess of electrons.
Typically at room temperature the voltage across the depletion layer for silicon
is about 0.6 – 0.7 volts and for germanium is about 0.3 – 0.35 volts. This
potential barrier will always exist even if the device is not connected to any
external power source, as seen in diodes.
Advantage: The world is going to be easy by using this
diode day by day.

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P-n Junction I-V Characteristics:
In Equilibrium, the Total current balances due to the sum of the individual components,

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Submitted by:
Robioul Hasan
BSC in EEE,
City University of Bangladesh.
Facebook.com/Robioul999
Thank You.