P N Junction - Meaning, Formation, Applications, FAQs

Edited By Team Careers360 | Updated on Nov 12, 2024 02:05 AM IST

The P-N junction is a fundamental concept in semiconductor physics, serving as the building block for various electronic devices. Formed by joining p-type and n-type semiconductors, this junction creates an essential interface with unique properties that govern the behaviour of diodes, transistors, and many modern electronic circuits. Understanding the formation of pn junction, its working principle, and its wide range of applications is crucial for grasping the core of modern electronics. In this article, we will explore the meaning, formation, and key applications of P-N junctions, along with answers to frequently asked questions (FAQs).

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What is PN Junction Class 12?
Formation of PN Junction Diode
Working of PN junction diode
Applications of PN junction diode

P N Junction - Meaning, Formation, Applications, FAQs

What is PN Junction Class 12?

Definition of pn junction diode class 12: A pn junction is defined as a boundary between the two types of semiconductor materials which are p-type and n-type in a single crystal of semiconductor. P-type semiconductors are those semiconductors that are formed by the doping of trivalent elements and have holes as the majority charge carriers. N-type semiconductors are those semiconductors that are formed by the doping of pentavalent elements and have electrons as the majority charge carriers.
PN junction diode

Formation of PN Junction Diode

When n-type and p-type semiconductors are joined to form a pn diode junction, several processes occur.

We know that the concentration of electrons is high in n-type semiconductors as compared to p-type semiconductors and the concentration of holes is high in p-type semiconductors as compared to n-type semiconductors.

$PN\ Junction Diode$

When an electron diffuses from n to p, it leaves behind an ionized immobile positive ion which accumulates at the n-side of the junction. Similarly, when a hole diffuses from p to n, it leaves behind an ionized immobile negative ion which accumulates at the p-side of the junction. This charge region on both sides of the junction is called the depletion region.

Due to this positive charge region on the n-side and negative charge region on the p-side of the junction, an electric field directed from positive charge to negative charge develops due to this electric field electrons on the p-side move to the n-side and hole on the n-side moves to p-side. This motion of charge carriers due to the electric field is known as drift current.

PN Junction Drift

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Working of PN junction diode

A pn junction diode is nothing but a pn junction provided with metallic contacts at both ends which are used to supply external voltage to the junction. It is a two-terminal device. The pn junction diode and its symbolic representation are shown below.

pn junction diode and its symbol

Biasing in PN junction diode

Biasing is a process of connecting the pn junction diode class 12 to the battery in order to provide the external input voltage. There are two different types of biasing methods depending upon which of the two terminals of the p-n junction are connected to which of the two sides of the battery.

Forward Bias: When an external voltage V is applied across the pn junction diode such that the p-side of the pn junction is connected to the positive terminal of the battery, the n-side of the pn junction is connected to the negative side of the battery, then the pn junction is forward biased.

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PN Junction in Forward Bias

Reverse bias pn junction: When an external voltage V is applied across a pn junction diode such that the p-side of the pn junction is connected to the negative terminal of the battery and the n-side of the pn junction is connected to the positive side of the battery, then the pn junction is reverse bias pn junction.

PN Junction in Reverse Bias

VI characteristics of the diode of pn junction

The Vi characteristics of the diode of the pn junction are shown below. It represents the change in current with respect to a change in voltage or vice-versa. The x-axis represents voltage and the y-axis represents current. The VI characteristics of the pn junction can be explained according to three conditions.

Condition :

Zero bias: In this condition there is no external voltage is applied, hence the potential barrier is high and the circuit current is 0.
Forward bias: In the forward bias condition, the external voltage is applied which results in the reduced potential barrier and hence the current flows in the circuit.
Reverse bias pn junction: In the reverse bias pn junction condition, the external voltage is applied but this time potential barrier increases. A small amount of reverse saturation current flows but on increasing the applied voltage, the diode will break.

VI characteristics of pn junction

Applications of PN junction diode

There are some of the common and important application of pn junction diode given below:

It has the potential to be used as a solar cell.
When the pn junction diode is reverse-biased, it can be used as a photodiode because it is sensitive to light.
In forward-biased conditions, the pn junction diode can also be used in LED lighting applications.
It is used in many electric circuits as a rectifier because it allows the current to flow only when the circuit is forward-biased.

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Frequently Asked Questions (FAQs)

1. Define diffusion current and drift current in pn junction diode.

The current induced when the electrons diffuse from n-side to p-side and holes diffuse from p-side to n-side in the pn junction due to concentration gradient is called diffusion current.

There is a movement of minority charge carriers of p-side and n-side from p ? n and n ? p due to the electric field of charges of depletion region. This motion of charge carriers due to electric field is known as drift current.

2. Define forward biased pn junction diode.

When the p-side of the pn junction is connected to positive terminal of battery, n-side of the pn junction is connected to the negative terminal of the battery, then the pn junction is forward biased.

3. Define Reverse bias pn junction diode.

When the p-side of the pn junction is connected to -ve terminal of the battery and n-side of pn junction is connected to the positive terminal of the battery, then pn junction is reverse bias pn junctioned.

4. Differentiate between n-type semiconductors and p-type semiconductors?

In p-type semiconductors doping is done by a trivalent element and holes are majority charge carriers. Whereas, in n-type semiconductors doping is done by a pentavalent element and electrons are majority charge carriers.

5. What is depletion region in pn junction?

A thin layer on both p and n side of pn junction which consist of ionized immobile negative and positive ions left behind by electrons and holes during diffusion is known as depletion region.