What is P-N junction diode ?

A p-n junction diode is a semiconductor device which consists of a junction between two different types of semiconductor materials viz. p-type (positively doped) and n-type (negatively doped). In the p-type region, there is an excess of positively charged carriers (i.e. holes) due to the presence of suitable dopant. In the n-type region, there is an excess of negatively charged carriers (i.e. electrons) due to a different dopant.

The two primary materials used in pn junction diode construction are silicon (Si) and germanium (Ge). These materials are chosen for their semiconducting properties and their ability to form a PN junction with the desired characteristics. Both silicon and germanium can be doped to create p-type and n-type regions to form "PN junction". Dopping involves introducing impurities into the semiconductor crystal lattice to create either excesss of holes (i.e. p-type) or excess of electrons (i.e. n-type). P-type dopants include boron (B), gallium (Ga) and indium (In). N-type dopants include phosphorus (P), Arsenic (As) and Antimony (Sb).

As shown in the figure, PN junction diode is a 2 terminal polarity sensitive device. The diode conducts when forward bias is applied and it will introduce zero resistance in the circuit. The diode does not conduct when reverse bias is applied and it will introduce infinite resistance in the circuit.

By careful controlling the doping process, semiconductor manufacturers can create PN junctions with specific electrical characteristics suitable for various applications such as rectification, voltage regulation, signal modulation and so on.

Uses or applications of PN junction diode

PM junction diodes are widely used in electronics due to their unique properties. The most common applications of PN junction diode are as follows.
➨Rectification : One of the primary uses of pn junction diode is rectification, where it converts AC (Alternating Current) to DC (Direct Current). When it is connected in proper configuration, it allows current to flow in one direction only, blocking the reverse direction.
➨Signal demodulation : Diodes are used to recover original modulation signals from AM or FM modulated waveforms.
➨Clipping : It can limit voltage levels of the signals which prevents them from exceeding certain thresholds.
➨Clamping : It can be used to clamp a waveform to a certain DC level by preventing it from going below or above a specific threshold. Hence it maintains specific voltage levels in circuits and protect components from voltage spikes.
➨Current steering : Diodes are used in circuits for current steering which ensure that current flows in specific direction under certain conditions. It is used in applications like overvoltage protection etc.
➨Diode logic circuits : They are used to implement basic logic functions such as OR, AND, NOT gates.
➨Voltage drop : Diodes are used to create fixed voltage drop in a circuit so that it can be used as voltage references.
➨The other applications of p-n junction diode are voltage regulation (using zener diode), voltage multiplication, LEDs, photodiodes, photovoltaic cells, temperature sensing, spike suppression, frequency generation, microwave and RF applications and so on.

Conclusion : As mentioned, PN junction diodes are fundamental semiconductor devices with broad array of applications in electronics. The common uses of pn junction diode include rectification, voltage regulation, signal demodulation, clipping, clamping, current steering etc. They are also used in various electronic circuits such as voltage multiplier, diode logic circuits, photodiodes, LEDs, photovoltaic cells, RF and microwave applications and so on.

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