Applications of PN Junction Diode

This blog explains the applications of the PN Junction diode. To understand the application better, we need to know what is a PN junction diode and how it works. This blog also focuses on the minute details of the PN junction diode, which will help us better understand why the diode is used in such a way in the applications.

The PN Junction diode is a semiconductor device that is a combination of n-type and p-type semiconductor materials which are usually made of silicon or germanium. The n-type is always negatively doped and has electrons as its majority charge carriers and the p-type is always positively doped and has holes as its majority charge carriers.

What do we mean by positively or negatively doped, Doping is a technique that adds impurities into the materials so that excess holes or electrons can be made in materials. Without doping there will be free electrons or holes which makes the semiconductor materials like silicon useless in their original form.

The making of excess holes is said to be positively doped and it is usually done with the materials like boron or gallium injected in the p-side and the making of excess electrons is said to be negatively doped and is usually done with the materials like arsenic or phosphorus injected in the n-side.

We know that the PN junction is formed by combining the n-type and p-type semiconductor materials. These materials are doped negatively and positively respectively. Due to doping, there are excess electrons and donor ions on the n-side and there are excess holes and acceptor ions on the p-side. The free electrons from the n-side start diffusing towards the p-side and combine with the holes and the acceptor and donor ions are left alone. These ions become immobile and form the depletion layer.

This layer has both positive and negative ions that are immobile and they also contain few charge carriers that are thermally generated in this depletion region. These ions create an electric field and point from the positive ions to negative ions in this depletion region. An electric field that flows from the positive ions to the negative ions in the depletion layer creates a potential barrier that restricts the further flow of electrons from the n-side to the p-side. The synonymy for the potential barrier discussed here is built-in potential.

Now the PN Junction has the following three biasing conditions they are:

1. Zero Biased
2. Forward Biased, and
3. Reverse Biased

Zero Biased

This condition revolves around the idea of not applying the bias that io external voltage is given to the diode. The pure diode without any external electrical or voltage supply is the zero-biased PN Junction diode. This keeps the diode in a state of equilibrium.

Forward Biased

Forward biasing refers to the type of biasing that involves connecting the external voltage in such a way that the positive terminal is connected to the p-side and the negative terminal is connected to the n-side. This brings the potential that helps the good amount of charge carriers towards the PN junction. This leads to a decrease in the size of the depletion layer and causes the derailment from a state of equilibrium.

Reverse Biased

Reverse biasing is just opposite to forward biasing and involves connecting the negative terminal of an external voltage to the p-side and the positive terminal to the n-side. This leads to an increase in the size of the depletion layer. So the potential barrier also rises and the diode acts as a resistor in this condition as no current flows.

These PN junction diodes have various applications and are used in different ways because of their characteristics.

• Rectification
• Photodiode
• Demodulation of Signals
• Clipping Circuits
• LED Lighting
• Voltage-Controlled Oscillator
• Clamping Circuits
• Logic Gate
• Current Routing
• Forward Voltage

Rectification

The main application of this diode is that it can be used as a rectifier that converts the AC into DC as this diode has the properties that can make the current only flow in one direction and block the reverse direction. This diode can be used in both the half-wave and full-wave rectifiers. As the diode is forward biased it has little resistance and when it is reverse biased it has high resistance. This can be used in rectifiers.

Photodiode

The photodiode is a special type of the PN junction diode that uses light energy to produce an electric current. The diode acts as a photodiode when the PN junction is in reverse-biased condition. They are used in simple everyday life due to their linear response towards light illumination. These are used in applications like solar cells, logic circuits, detection circuits, and characteristics recognition circuits.

Demodulation of Signals

The diodes are also used in demodulating circuits where the diode acts as a rectifier and extracts the original waveforms from the AM or FM-modulated waveforms. The extraction is important as the signals are encoded into the carrier forms in the AM or FM-modulated waveforms. When the diode receives these signals in these forms it converts them into the original form.

Clipping Circuits

The diode is used in clipping circuits too. A clipping circuit is used to help in limiting the voltage levels so that they don’t exceed the threshold voltage level. These diodes help clip the signals due to their unidirectional nature so that signals don’t cross the threshold voltage limits. The diode is forward-biased during the positive half-cycle and reverse-biased during the negative half-cycle In the positive diode clipping circuit and the vice-versa in the negative diode clipping circuit.

LED Lighting

The LED is a special type of PN Junction diode that is heavily doped and when the current passes through this the electrons combine with the holes and this process leads to the emission of light. The LED emits different colors which is determined by the semiconducting materials used.

Voltage-Controlled Oscillator

The diode can also be used as a voltage-controlled oscillator. The non-linear characteristics of the PN Junction diode are exploited to form a voltage-controlled oscillator circuit and this is used in varactors. These diodes help in maintaining the voltage levels and limiting them from crossing the threshold value.

Clamping Circuits

Like the clipping circuits, these diodes can be used as the clamping circuits too. In clipping circuits, the signals were controlled and here the waveforms are monitored so that the waveforms don’t exceed a certain threshold voltage level. The clamping circuits control the levels of voltage so that waveforms don’t exceed certain threshold values. The diode can be used to clamp by redirecting the waveform and preventing it from exceeding a certain specific level of voltage.

Logic Gate

The PN Junction diode can be used in making logical gates or circuits by implementing basic logical functions like AND, OR, and NOT. These are used in digital circuits.

Current Routing

As we know these diodes are unidirectional they can be used in current routing or steering as we can ensure that the current flows in the desired direction which will be useful in preventing the excess current from going towards the sensitive components. This way it can be used to provide overvoltage protection.

Forward Voltage

The diodes usually create fixed voltage drops when they are forward-biased. This serves as a voltage reference for circuits which are generally used for voltage regulations.

The article briefly explores what is the PN junction diode and how they are constructed. This also summarizes the working of the PN Junction diode. We also saw the various applications of the diode used in various ways like signal demodulation, Current routing, forward voltage, clamping and clipping circuits, etc. The diode can also be used as a rectifier, photodiode, solar cell photovoltaic cell, etc. Hence, by modifying the biasing conditions of the diode, it can be used in distinct ways.

What is the special application of the PN Junction Diode?

The PN Junction diodes can be used as the photodiode. This is the special application of the PN Junction diode.

What is a Tunnel diode?

The tunnel diode is a diode that contains of one PN junction which is heavily doped from both sides and has a very narrow depletion layer.

Is PN Junction Unipolar?

No, The PN Junction is not unipolar, It is used in bipolar transistors.

What kind of device is a PN Junction diode?

The PN Junction diode is an active device.

Is PN Junction unidirectional or bidirectional?

The PN Junction diode is unidirectional in nature because current flows in one direction only.