The diode is a semiconductor device which allows the current to flow in one direction. Therefore, this device is also known as the unidirectional semiconductor device. In this article, we will learn about different types of a diodes.
It has two terminals; anode and cathode. The germanium, silicon, and selenium used to manufacture the diode.
Types of Diodes
There are several types of diodes available in power electronics circuit design. Out of that, we will discuss here,
- PN Junction Diode
- Zener Diode
- Light Emitting Diode
- PIN Diode
- Schottky Diode
- Tunnel Diode
- Varactor Diode
- Laser Diode
- Avalanche Diode
- Vacuum Diode
- Shockley Diode
- Gunn Diode
- BARITT Diode
- IMPATT Diode
- TRAPATT Diode
- Step Recovery Diode
So, Let’s start to explain in details for all types of diodes.
PN Junction Diode
The PN junction diode is a standard form of a diode and generally known as diode only.
It has two layers; one layer is doped with P-type material and the second layer is doped with N-type material. Both layers make a junction. Hence, this diode is also known as the PN junction diode.
This types of diodes operates in the forward region only. Therefore, it allows the current to flow in one direction and it will reject the current in reverse bias. Because of this type of characteristic, this diode is widely used in the rectifier.
The symbol of the PN junction diode is as shown in the below figure.
The Zener diode works on the principle of Zener breakdown. This diode has similar characteristics to the normal diode in a forward direction.
But the Zener diode is also allowing the current in reverse direction when the applied voltage reaches the breakdown voltage.
It enables a stable voltage to be produced if the supplied current is limited through a resistor. Therefore, Zener diode is widely used to provide a reference voltage in power supplies.
The symbol of the Zener diode is as shown in the below figure.
Light Emitting Diode
As the name suggests, it is a diode that emits light is known as the Light Emitting Diode. It abbreviates as LED for general purposes. It releases energy in the form of PHOTONS.
This phenomenon known as electroluminescence. This phenomenon discovered by the H.J. Round in 1907.
After the commercial production of LED, it used as a replacement of the incandescent and neon indicator lamps.
LED is a little bit different than the power diode or PN junction diode. The symbol of the LED is also slightly different than the symbol of a diode. The below figure shows the symbol of the Light Emitting Diode.
The PIN diode has nearly similar construction than the PN junction diode. But the only difference is that it has an intrinsic semiconductor with no doping in between the P-layer and N-layer.
This intrinsic semiconductor region will increase the area of the depletion region. And because of this type of construction, PIN diode is useful in switching applications.
The symbol of a PIN diode is as shown in the below figure.
The Schottky diode named after a German physicist Walter H. Schottky. In this diode, there is no PN junction. There is a small junction between N-type semiconductor and metal. The semiconductor material (N-Type) acts as an anode and the metal acts as a cathode. The material used for the metal is chromium, platinum, or tungsten.
This diode has a low forward voltage drop and fast switching. At low currents, the drop may be 0.15V to 0.4V. Because of this characteristic, this diode is widely used as a clamping diode. This diode is also used as a power diode for rectification of AC power.
The lower drop of diode will increase the efficiency of the device and therefore, it is also used in the RF applications. The symbol of the Schottky diode is as shown in the below figure.
Leo Esaki has invented the tunnel diode in 1958. So, this diode is also known as Esaki Diode. A tunnel diode heavily doped PN junction diode which works on the tunneling effect.
The junction barrier is very thin because of the heavily doped regions. And this allows the electron to escape easily. This phenomenon is known as the tunneling effect. Due to the tunneling effect, it can operate very fast in the microwave frequency region.
This diode is not used in many applications in the present day. But this diode was used in microwave applications and amplifiers. The symbol of a tunnel diode is as shown in the below figure.
The varactor diode also known as varicap diode or variable controlled capacitor. This diode has P-layer and N-layer and a junction. The width of the depletion region is not constant, it varies according to the amount of bias place on it.
The diode works as a variable capacitor. According to the width of the depletion region, the capacitance is varying. And the width of the depletion region can vary by varying the reverse bias. In this way, it is also possible to control the capacitance.
This diode used as a voltage-controlled oscillator for cell phones, satellite pre-filter. The symbol of the varactor diode is as shown in the below figure.
The working principle of Laser diode is similar to the Light Emitting Diode. Because both diodes convert an electrical form of energy into light energy. But the laser diode generates the laser light.
The laser diode has a PIN junction. Where (I) represents the intrinsic junction. The holes and electrons are combining in the intrinsic junction and generate a laser beam.
These diodes widely used in applications like CD and DVD drives, laser printer, optical communication, and laser light pointer for PPT presentation.
The cost of this diode is very high compared to other diodes but this cost is very less compared to other laser beam generators. The symbol of a laser diode is as shown in the below figure.
The avalanche diode designed to operate in the avalanche breakdown region. This diode can work in reverse bias condition. When a sufficient amount of voltage is given in reverse bias, minority carrier ionized and start to flow the current in reverse bias.
Electrically, avalanche diode works similarly to the Zener diode. But in the Zener diode, the doping concentration is higher as compared to the avalanche diode. Therefore, the Zener diode creates a small junction. And it can break at low voltage also.
An avalanche diode, because of the low doping concentration, it has a wide junction. Therefore, it needs high voltage to breakdown. This wide junction makes avalanche diode a good surge protector compared to the Zener diode.
The symbol of the avalanche diode is as shown in the below figure.
Vacuum diode has two electrodes which work as an anode and cathode. This is the simplest form of a diode. Both electrodes are enclosed in a vacuum tube.
The cathode made up of tungsten. When it heats up it emits electrons in the direction of anode. The cathode is coated with oxide material which used to increase the electron emission capability.
In forward bias, the free electrons on cathode release into a vacuum tube. The anode collects these electrons and the current flows through the tube.
In reverse bias, the current will not flow through the vacuum tube because the free electrons in the vacuum get repelled by the anode as it connected to the negative terminal.
Sometimes, the cathode surface kept rough to reduce the temperature developing in the diode. The symbol of a vacuum diode is as shown in the below figure.
This diode has four layers and it also known as PNPN diode. This diode is similar to the SCR without the gate terminal.
Similar to the SCR, Shockley diode also stays ON once it turned ON and stays OFF once it turned OFF.
It has no gate terminal. So, there is the only way to switching ON is by applying forward voltage greater than the forward breakdown voltage.
In conduction mode, it will not be turned off if the forward voltage is less than the forward breakdown voltage. It acts as a relaxation oscillator and triggers switches for SCR.
The symbol of the Shockley diode is as shown in the below figure.
This diode doesn’t have the PN junction. Therefore, it does not work like a normal diode. The Gunn effect was discovered by J. B. Gunn. And after his name, this diode is known as Gunn diode. This diode also known as “Transferred Electron Device”.
It has three N-type layers. Two N-type layers placed at both terminals and these layers are highly doped. The middle layer is a thin layer with lightly doped.
When the voltage applied to the Gunn diode, the current increases with an increase in voltage. The resistance of the middle layer starts increasing at a higher voltage and it results in the fall of the current flow. This is the negative resistance region and, in this region, the diode will operate.
This diode used as an oscillator for generating microwaves of high frequency. The symbol of the Gunn diode is as shown in the below figure.
When light strikes on the photodiode, it will generate holes and electrons. Therefore, it allows the current to pass.
The photodiode used as a light sensor. It used in line follower and obstacle avoider robots. It also used in solar cells and photometer and sometimes it used to generate electricity. The symbol of a photodiode is as shown in the below figure.
BARITT is a short form of Barrier Injection Transit Time. This diode works on the principle of thermionic emission. Therefore, it will give a noise-free operation.
The operating frequency range of this diode is between 4 GHz to 8 GHz and efficacy is very low between 5% to 20%. The output power of this diode is just a few milliwatts and used for the microwave signal generator.
It also used in burglar alarms and where it can create a simple microwave signal with a low noise level.
IMPATT stands for Impact Ionization Avalanche Transit Diode. It is a high-power semiconductor component and used in high-frequency microwave devices.
This diode can operate at a frequency between 3 GHz & 100 GHz. The main advantage of this diode is its high-power capability. The disadvantage of this diode is the noise level.
The applications of this diode are low-power radar systems, proximity alarms, etc.
TRAPATT is a short form of Trapped Plasma Avalanche Triggered Transit Mode. This diode used as a microwave oscillator.
The operating frequency range is between several hundreds of MHz to several GHz. It belongs to the IMPATT family.
This diode gives higher efficiency than the IMPATT diode. The disadvantage is the noise level on the signal.
Step Recovery Diode
The step recovery diode is also known as the snap-off diode or charge-storage diode. This is a special diode that stores the charge in a positive pulse and uses this charge in a negative pulse of sinusoidal signals.
This diode used in higher-order multipliers and pulse shaper circuits. The cut-off frequency of this diode is very high (in terms of GHz).
These types of diodes relies on the fast turn off characteristic for their operation. The symbol of this diode is as shown in the below figure.
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