It is an electronic device in which the electric current flows in one direction. The diode is the most used semiconductor device in electronics circuits. Usually, they are used as rectifier for rectification. Nowadays, several different types of diodes having different properties are available.
Some of the different types of diodes with their properties and applications are discussed below
P-N Junction Diode
- A PN Junction Diode is one of the simplest semiconductor devices around, and which has the characteristic of passing current in only one direction, current flows in forward direction and blocks it in backward direction. This diode is made up of semiconductor material. It is made up of two layers of semiconductors. One layer is doped with P-type material while the other layer is doped with N-type material. The combination of the both P and N-type layers form a junction known as the P-N junction. Hence it is called as P-N junction diode.
Small Signal Diode
- Small Signal Diode is the type of P-N junction diode which operates on low voltage signals. It is small non-linear semiconductor devices generally used in electronic circuits; its junction area is very tiny. Because of that, the junction has less capacitance & low charge storing capacity. It enables the small signal diode to have high switching speed with very fast recovery time.
Rectifier Diode
- Rectifier Diode is a type of P-N junction diode. It has very large P-N junction area. Because of that, the junction has high capacitance in reverse direction. It has low switching speed. It is also used to convert alternating current (AC) to direct current (DC) and this process is called rectification. This diode is most commonly used.
Schottky Diode
- A Schottky diode is a type of semiconductor diode formed by the small junction of n-type semiconductor with a metal. Therefore, it is also known as the hot-carrier diode or Schottky barrier diode. The advantage of the Schottky diode is that it has very low forward voltage drop and fast switching speed. The drawback of Schottky diode is that it has low reverse breakdown voltage and high reverse leakage current.
Super Barrier Diodes
- Super Barrier Diodes are also known as rectifier diode. They are next generation Schottky diode. This diode is designed for high power, low loss and fast switching application. They have low forward voltage drop like schottky diode. SBR (Super Barrier Diodes) have low reverse leakage current than schottky diode.
Light Emitting Diode (LED)
- LED (Light Emitting Diode) is a light releasing diode which glows when an electric current flows through it. It is a light source based on semiconductors. It is widely used as a standard source of light in electrical equipment. LED converts electrical energy into light energy.
Photodiode
- A Photodiode is a semiconductor p-n junction device that converts light into an electrical current. The current is generated when photons are absorbed in the Photodiode. It converts the incident light into the electric current. It is a type of P-N junction diode. Its operation is opposite to that of an LED.
Laser Diode
- Laser diode is a semiconductor device which is similar to a light emitting diode (LED) as it directly converts electrical energy to light energy. Laser diode produces consistent light. This coherent light is formed by the laser diode using a method termed as “Light Amplification by Stimulated Emission of Radiation”, which is abbreviated as LASER.
Tunnel Diode
- A Tunnel diode is a type of semiconductor diode which has “negative resistance”. The region where negative resistance occurs is known as negative resistance region. It is a heavily doped P-N junction diode about 10nm wide, and works on the principle of tunneling effect. A tunnel diode is one of the most commonly used negative conductance devices. (It is also known as an Esaki diode)
Zener Diode
- Zener diode is a diode which allows the flow of current in both directions; forward as well as backward direction. It allows the current to flow in backward direction when a certain set of reverse voltage is applied, that reverse is nothing but a zener voltage. It has very thin depletion region, as they have heavier doping concentration as compare to normal P-N junction diode.
Backward Diode
- A Backward diode is a variation to zener diode and tunnel diode. It has operations similar to that of zener diode and tunnel diode, but having much lower operating voltages as compare to them. It is also known as back diode. It is not used widely but it can be used for rectify small voltage signal (0.1 to 0.6v). Due to its fast switching speed, it can be used as a switch in RF mixer and multiplier.
Avalanche Diode
- The Avalanche diode is a type of P-N junction diode that is particularly designed to operate the avalanche breakdown region. Avalanche breakdown is a phenomenon where adequate amount of reverse voltage is applied to the P-N junction. However, the minority charge carrier ionizes & starts a flow of heavy current in reverse direction. Avalanche diode has similar function to that of the Zener diode. However, the doping concentration of a avalanche diode is relatively lower as compared to an Zener diode.
Transient Voltage Suppression (TVS) Diode
- Transient voltage suppression diode is a type of avalanche diode which protects the circuit from high voltage surges. This diode may be either unidirectional or bidirectional. Unidirectional TVS (Transient voltage suppression) diode operates similar to avalanche diode, as it acts as a rectifier in forward bias & surge protector in reverse bias. Bidirectional TVS (Transient voltage suppression) diode acts as two avalanche diodes opposing each other in series.
Gold Doped Diode
- In this type of diode, gold and platinum is used as the dopant (doping material) in diode. Gold Doped Diode has fast switching speed and reverse leakage current is also high compared to normal P-N junction diode. Even at the higher voltage drop gold doped diode allows the diode to operate in signal frequencies.
Constant Current Diode
- A Constant Current Diode is id diode which limits the current to a maximum specified value. It is also identified as Current-Limiting diode (CLD) or Current-Regulating diode (CRD). These diodes are actually JFET with gate. They are shorted to the source with gate. It limits the currents same as zener diode which limits the voltage.
Step Recovery Diode
- A Step Recovery diode (SRD) is a semiconductor junction diode which has the ability to generate extremely short pulses. It is also known snap-off diode or charge-storage diode. It is a P-N junction diode which abruptly ceases the flow of current when its direction is reversed. As a result, SRDs can provide very fast voltage transitions with the very sudden disappearance of the charge carriers.
Peltier or Thermal Diode
- Peltier or Thermal diode is a type of diode which allows flow of heat in one direction and whose thermal resistance is different in one direction than in other direction. This type of diode is used in the application of heat monitoring in microprocessor and in refrigerators for cooling effect.
Vacuum Diode
- Vacuum diode is the simplest form of a diode made from vacuum tubes and two electrodes (anode and cathode). The anode and cathode are enclosed inside the vacuum tube. It is an electronic device which allows the flow of current in one direction i.e.; cathode to anode and block the flow of current in another direction i.e.; anode to cathode.
Varactor Diode
- Varactor diode is a type of diode whose internal capacitance varies with respect to the reverse voltage. It always works in reverse bias condition. These diodes have a P-N junction with. The depletion layer between the P and N-type material always vary due to change in reverse voltage. Varactor diode is the only diode which is able to use this effect with a high range of capacitance.
Gunn Diode
- Gunn diode is a two-terminal semiconductor electronic component form of diode, which has negative resistance. It is used in high-frequency electronic devices. It is consists of only N-doped semiconductor material, but the majority diodes consist of both P and N-doped regions, which is why it does not rectify AC or work like a normal diode. It is also known as “Transferred Electron Device” (TED) instead of a diode.
PIN Diode
- A Pin diode is a diode which has wide region of undoped intrinsic semiconductor between P-type and N-type semiconductor region. In reverse bias, the wide intrinsic layer in the diode can block and accept high reverse voltages. It will act as a linear resistor at higher frequency. It is because of the fact that the PIN diode has poor reverse recovery time. At low frequency, it acts as a rectifier diode
Silicon Controlled Rectifier (SCR)
- Silicon Controlled Rectifier is a four-layer solid-state current-controlling device. It has three terminals Anode, Cathode, and Gate. SCR is basically a diode which has an external control input further which is known as gate input. This diode allows the current to flow in only one direction. But when SCR is connected in forward bias it blocks the flow of current and is known as forward blocking mode. SCR is used for controlling high power circuits, rectification of high power AC
Shockley Diode
- Shockley diode is a four layer P-N-P-N semiconductor diode which is the first semiconductor device invented. It is a P-N-P-N diode, with alternating layers of P-type semiconductor and N-type semiconductor materials. It resembles SCR but it has no control or gate input. Shockley diode tends to stay ‘ON’ once it is turned ‘ON’ & tends to stay ‘OFF’ when it is turned ‘OFF’. The Shockley diode has no gate input so it has the only way to switch it ‘ON’ is by applying the forward voltage which is greater than its breakdown voltage. As we apply the forward voltage which is greater than its breakdown voltage, it will allow the flow of an electric current.
Point Contact Diode
- Point Contact Diode is a type of diode in which a small point junction is formed between a metal wire & N-types semiconductor crystal. It is also known as Cat Whisker diode or Crystal diode. This diode is a thin springy wire made of Phosphorus bronze or tungsten. It makes a point contact junction with an N-type semiconductor, Hence the name point-contact diode. As the junction formed is very small so the junction capacitance of point contact diode is very low. Point contact diodes are used for low voltage signal & in microwave mixer & detectors.