Special Purpose P-N Junction Diodes

This is a post about the Special Purpose p-n Junction Diodes. It will give you more information on this topic. 

The Zener diode is an important semiconductor device used as a light detector. Zener diodes have a specific voltage (about 1.25 V) corresponding to the point where light emission ceases in vacuum-sealed tubes. It was invented in 1924 by Harvey G.

The Zener diode is a special type of P-N junction diode. It has a high breakdown voltage (about 10 kV for GaP), low forward resistance, and a fast turn-on time of about 0.5 nanoseconds (ns).

Diodes

If a diode is placed in an external circuit, current will flow through it in one direction but not the other. In its simplest form, a diode is constructed from a single p-n junction with a metal contact on one side and an electrically conductive semiconductive region on the other. It acts as a one-way valve for electric current. If the applied voltage is reversed, the current will not flow through the diode because its p-n junction does not allow the current to pass in this direction. While the p-n junction is forward biassed, a small leakage current flows, and the diode acts as a low resistance conductor. When the diode is reverse biassed, no current will flow even if a voltage higher than the breakdown voltage is applied (“breakdown voltage” is called “maximum operating voltage”).

Junction diode

This is a semiconductor junction device used to regulate a dc voltage. It is usually used in the output section of the circuit. The design of this circuit depends on the requirement, whether it is driving a load or not, and many other factors which determine the type of decision to be made; therefore, there are several types of junction diodes.

Rectifier

A device that converts alternating current to direct current. The term has various meanings in different electrical applications. Still, in electronics, the term most often refers to a solid-state device that converts AC to DC using four semiconducting junctions arranged in either a full-wave or half-wave configuration.

Full-wave rectifier

A full-wave rectifier consists of a semiconductor with two p-n junctions (forward-biassed and reverse-biassed) connected in series, with an alternating current applied to the positive terminal (a). The p-n junctions are in a very thin material region where the electric field is stronger.

Zener diode

The Zener diode is a voltage-regulated semiconductor device. It consists of a p-n junction diode, in which the reverse breakdown voltage is not under the forward bias condition. The important function of this device is to provide a constant voltage level, regardless of the variations in voltage due to temperature changes. A Zener diode is made from silicon and a few other materials, including graphite as an electrical conductor.

The Zener Diode always has a negative temperature coefficient (NTC).

Optoelectronic junction devices

• The devices that require specific characteristics to be determined are called optoelectronic junction devices. 

• This device is usually used in high-speed switching circuits in the optical domain. These optoelectronic junction devices are usually used in transmitting and receiving functions of telecommunications equipment, computers, and consumer electronics products.

• Si and GaAs are preferred materials for solar cells. The solar panels are made with these materials. These cells are used for applications such as lighting, watches, digital calendars, and the rectification of high-frequency signals when there is no access to a power supply.

• Another usage of the p-n junction is in infrared (IR) signal diodes used in remote control devices like TV and DVD players to signal emissions from the remote control unit. 

Uses and applications

1. Telecommunication

• As protecting diodes for bipolar transistors and thyristors in power electronics,

• as voltage regulators and frequency converters in integrated circuits,

• as photodetectors in optical communication systems.

2. Optical instruments

• Photodetector in optical measuring instruments

• Photomultiplier in optical metres and instruments

3.  Communication systems

• In light emission and detection and light modulation devices.

• In photocells and solar cells.

4. Medical engineering

• As semiconductor laser spectroscopic detector for the determination of trace gases in ambient air,

• For the detection and separation of cells for a simple one-component cell cytometer,

• In molecular diagnostics to detect DNA, RNA, and protein.

5. Assembling solar panels

• Charge separation in bipolar transistors at the electrodes during current injection, with the positive charges being responsible for charge splitting. The charge separation produces a voltage across the junction proportional to the amount of charge injected. The charge injected depends on current, temperature, and doping concentration.

• The amount of light that passes through the junction is determined by the bias voltage at the solar cell. This could operate either as an optical detector or an optical rectifier.

Conclusion

The p-n junction diode is a semiconductor junction formed by diffusing two different kinds of impurity elements into a zone. The two materials are one type of doping (n-type), and the other is another type of doping (p-type).

A Zener diode is a p-n junction used for regulating current and voltages in electrical circuits. It is also used as a voltage regulator.

It uses the phenomenon of avalanche breakdown in semiconductors, which is the abrupt increase in reverse current when the reverse voltage applied across a p-n junction exceeds a certain level called the breakdown voltage noted as V.