Diode – It is a two-terminal electronic component, which conducts current mainly in only one direction. An ideal diode will have zero resistance on one end and high resistance on another end. The most common type of diode is semiconductor diode. They are primarily made up of silicon and germanium is also used. Generally, diodes are used for rectification.

Types of Diodes – There are several types of diodes are discussed below –

1. Laser diode – It is a type of diode that produces coherent light and is highly used in laser devices, CD drives, and DVDs. The laser diode is more expensive than LEDs and cheaper as compared with laser generators. A laser diode is similar as compared with an LED as it converts electrical energy into light energy but it also produces coherent light. It is also used in laser printers, optical communication, laser pointer, and many more.
2. Light Emitting Diode (LED) – It is also a type of p-n junction diode, which emits light in the forward-biased configuration.  In this type of diode, when an electric current between the electrodes passes through the diode then light is produced. Light Emitting Diode (LED) is made up of a direct-band semiconductor. In other words, LED converts electrical energy into light energy.
3. Photodiode – It is that type of p-n junction diode in which it converts light energy into electric current. The work of a photodiode is opposite to that of a Light Emitting Diode (LED). It is a reverse-bias diode and is used in photometers and solar cells.
4. Rectifier Diode – It is the most used and most common type of diode. A rectifier diode is a type of p-n junction diode whose p-n junction area is very large which results in high capacitance in the reverse direction with low switching speed. Rectifier diode is the most used and common type of diode that can handle heavy electric current are also used to convert alternating current (AC) into direct current (DC).
5. Schottky Diode – It is a type of diode that consists of a small junction between an N-type semiconductor and a metal.  But it has no P-N junction. The main benefit of this type of diode is that it has a very low forward voltage drop and fast switching. Due to no capacitive junction (p-n junction) in this type of diode, the switching speed is very fast
6. Tunnel Diode – Leo Esaki invented the Tunnel Diode in the year 1958 and received the Nobel prize in 1973 that’s why the Tunnel diode is also known as the Esaki diode. This type of diode is a heavily doped P-N junction diode that works on the principle of the tunneling effect. The junction barrier becomes very thin due to heavy doping concentration. It also allows the electron to simply escape through the barrier and this phenomenon is called the tunneling effect. This type of diode also conducts current in the reverse direction and it is a fast-switching device.
7. Small Signal Diode – It is a type of p-n junction diode that operates on low voltage signals. Due to its junction area being very small, it has low charge storing capacity and less capacitance. This type of diode also enables the small signal diode with high switching speed and very fast recovery time.
8. Super Barrier Diodes – These diodes are also similar as rectifier diodes but they have a low forward voltage drop that is the same as a Schottky diode. This type of diode also has a low reverse leakage current that is similar to a p-n junction diode.
9. Zener Diode – This type of diode allows the flow of current in the forward direction. It also enables the flow of current in the reverse direction when the reverse voltage reaches the breakdown voltage is called as Zener Voltage and allows the current flow. This type of diode has a heavier doping concentration as compared with normal p-n junction diode thus it has a very thin depletion region. Mostly it is used in reverse bias configuration that provides a stabilized voltage for the protection of circuits from overvoltage.
10. Avalanche Diode – This type of diode is a p-n junction diode that is specifically designed for operating in the avalanche breakdown region. Avalanche breakdown is a phenomenon in which an adequate amount of reverse voltage is applied to the p-n junction. Thus, the minority carrier ionizes and starts a huge amount of current flow in the reverse direction.
11. Gold Doped Diode – It is a type of diode in which platinum or gold is used as the doping material that enables the diode to operate at a fast-switching speed but at the expense of enhancing the forward voltage drop. Hence, the reverse leakage current is higher as compared with a normal p-n junction diode.
12. Peltier or Thermal Diode – It is a type of diode in which thermal resistance is different in one direction than the other direction. Thus, the heat produced flows in one direction to one side and leaves the other side cooler. This type of diode is used in the application of cooling effects in refrigerators and microprocessors for heat monitoring.
13. Varactor Diode – It is also called as Vericap diode which is voltage-controlled capacitors. It also has a p-n junction with variable junction capacitance. This type of diode operates under reverse bias conditions. In this type of diode, the depletion layer between the P and N-type material is varied by changing the reverse voltage.
14. PIN Diode – This type of diode is a three-layer diode that is P-layer, I-layer, and N-layer in which the I means Intrinsic semiconductor layer which is situated between heavily doped P and an N-type semiconductor. In this type of diode, the electron and holes from N and P-type respectively flow to the intrinsic region thus once the I region fills completely with electron holes, the diode starts conduction. This type of diode is used in high-voltage rectification in RF applications as a switching & attenuator element.
15. Shockley Diode – It is a four-layer PNPN diode that resembles SCR with no control or gate input. As the type of diode has no gate input thus the only or one way to switch ON through applying the forward voltage is larger than its breakdown voltage. When you will apply the forward voltage is larger than its breakdown voltage then it enables the flow of current.
16. Point Contact Diode – It is a type of diode where a small point junction is formed between an N-type semiconductor crystal and a metal wire and is also called as Crystal diode or Cat Whisker diode. This type of diode is used in low-voltage signal detectors and microwave mixers.