PN junction Diode – Definition, Formation, Applications, 7 Advantages and Disadvantages.

When a p-type semiconductor is brought in close contact with an n-type semiconductor by stable means, the arrangement of both the semiconductors is known as the PN junction.

The interface of p-type and n-type semiconductors is called Junction. Two independent p-type and n-type semiconductors pressed against each other do not form a PN junction. 

Introduction to PN junction Diode

What is pn junction diode?

When a single piece of semiconductor material (either Si or Ge)  whose one portion is doped with an n-type impurity and the other portion is doped with p-type impurity behave as a PN junction. A PN junction having metallic contact at its end is known as the PN junction diode. 

PN junction diode diagram

The most basic property of junction diodes is that it conducts an electric current in one direction and does not allow it to flow in the other direction.

PN junction diode symbol 

Symbolic representation of pn junction diode is given below

The arrow head represent p type semiconductor and the bar represent n type semiconductor. The arrow further represent the direction of conventional current through the diode.

Types of pn junction diode

There are 2 main types of pn junction diodes:

1. Conventional/Standard diodes.
2. Schottky diodes.

Energy band diagram of pn junction diode

What is the working principle of pn junction diode?

A pn junction diode’s working principle is based upon the flow of electrons, holes and photons. A pn junction is a combination of a p-type semiconductor material and an n-type. This creates a region of depletion where electrons and holes can be separated.

It allows for only one-way current flow. The diode can conduct if a positive voltage (for the p-type) is applied and a negative voltage (for the n-type). The diode acts as an insulator when a reverse voltage can be applied.

Continuity equation in pn junction diode

In a pn junction diode, the continuity equation states that the current flow rate of charge carriers (electrons and holes) through the diode must be constant regardless of changes in the electric field. The continuity equation can be given by

dN/dt + Jn = 0 for electrons

dP/dt – Jp = 0 in holes

N and P represent the respective concentrations of electrons or holes, Jn, Jp, and dN/dt, respectively, the rates of change in electron and hole concentrations. The continuity equation is used to analyze the current-voltage characteristics and the behavior of charge carriers within a pn junction.

Formation of PN Junction

There are three main methods for the formation of pn junction diodes:

1. Diffusion Method.
2. Ion implantation method.
3. Epitaxy method.

These three methods can produce high quality pn junction diodes that have well-defined electrical characteristics. This makes them suitable for a variety of applications. The type of semiconductor material used, the desired electrical characteristics and the manufacturing process will all play a role in the choice of the method

Junction barrier or barrier potential

The depletion layer contains positive and negative immobile ions. These positive and negative Ions are separated by a distance equal to the thickness of the depletion layer.

Thus, a potential difference is set up across the junction which opposes the further diffusion of electrons and holes through the junction. The potential difference is called a potential barrier or junction barrier. 

Characteristics of pn junction diode

Basically there are 2 types of characteristics of pn junction diode.

• Forward bias characteristics.
• Reverse bias characteristics.

Application of pn junction diode

PN junction diode has many application in electronics which makes the life easy. Some of the applications are as follow.

1. PN junction diode is used for Rectification of input and out signals.
2. Clipping and Clamping digital circuits.
3. PN junction is used for Voltage regulation.
4. In Switching.
5. Signal detection.
6. Power supply digital circuits.
7. Used for LED lighting.
8. Solar cell applications.
9. Voltage multipliers.

7 Advantages of pn junction diode

7 Disadvantages of pn junction diode

1. Reverse voltage is limited: PN junction diodes are not suitable for high-voltage applications due to their low reverse voltage rating.
2. Non-linear characteristics in current-voltage: The current-voltage properties of PN junction diodes can cause distortion in applications like rectification.
3. High reverse leakage current: PN Junction diodes have a large reverse leakage current. This can lead to power losses in reverse-biased situations.
4. Low frequency response: PN junctions diodes are not suitable for high-frequency applications due to their limited frequency response.
5. Temperature Sensitivity: PN junction diodes can be affected by temperature. This can cause their forward voltage drop or reverse leakage current to decrease.
6. Reverse recovery time is limited: PN junction diodes only have a short reverse recovery time. This can lead to high switching losses in fast-switching situations.
7. Limitation on voltage blocking ability: PN junction diodes are limited in their voltage blocking capabilities, which limits their use for high-voltage applications.

Also read these post related to pn junction diode.
1. Characteristics of pn junction diode
2. 7 main differences between forward bias and reverse bias
3. PN junction diode forward and reverse bias

FAQ’s on pn junction diode