Applying of potential difference across a semiconductor device with a standard polarity is called Biasing. There are mainly two types of Bias, one is Forward Bias and another one is Reverse Bias. Biasing is needed to provide with some semiconductor devices such as PN Junction Diode, Zener Diode, Schottky Diode,  etc. In this article, we are going to understand forward and reverse bias with the example of PN Junction Diode Biasing.

## What is Forward Bias or Forward Biasing?

When the positive terminal of the battery is connected to the P-type semiconductor and the negative terminal of the battery is connected to the N-type semiconductor, then it is called Forward Bias or Forward Biasing.

In the case of Forward Biasing of  PN Junction diode, the positive terminal of the battery is connected to the p-type region and the negative terminal of the battery is connected to the n-type region. Here, you can see the diagram below.

In the forward bias condition, the potential barrier of the PN Junction diode reduces and can conduct current. In this case, the width of the depletion region is also very low.

We know that the same polarity always repels to each other and opposite polarity always attracts each other.

So, as in the forward bias condition, the p-type region is connected to the positive terminal of the battery, and the holes in the p-type region repel and move toward the junction.

On the other hand, the n-type region is connected to the negative terminal of the battery, so electrons in the n-type region also repel and move towards the junction.

As a result, the width of the depletion decreases and the potential barrier is broken down, so currents start flowing through the diode.

In the forward bias condition, the PN Junction diode acts as a conductor, and the flow of current depends upon the applied forward voltage.

## What is Reverse Bias or Reverse Biasing?

When the positive terminal of the battery is connected to the N-type semiconductor and the negative terminal of the battery is connected to the P-type semiconductor, then it is called Reverse Bias or Reverse Biasing.

In the case of Reverse Biasing of the PN Junction diode, the positive terminal of the battery is connected to the n-type region and the negative terminal of the battery is connected to the p-type region. Here, you can see the diagram below.

In reverse bias condition, the depletion region of the PN Junction diode increases and it cannot conduct current.

As in the reverse bias condition, the p-type region is connected to the negative terminal of the battery, the holes in the p-type region attract and move away from the junction.

On the other hand, the n-type region is connected to the positive terminal of the battery, so electrons in the n-type region also attract and move away from the junction.

As a result, the width of the depletion increases, and the potential barrier becomes stronger, so current cannot flow through the diode.

In reverse bias conditions, the PN junction diode acts as an insulator, and can not conduct current through it.

## Example and Application of Forward Bias

Most of the time, semiconductor devices are used with forward bias. For example, when a PN junction Diode is used in a rectifier circuit, it needs forward biasing. When the Zener Diode is used for over-voltage protection, then it is connected with forward bias.

## Example and Application of Reverse Bias

When the Zener diode is used for voltage regulation purposes, then it is connected in reverse bias. When the PN Junction diode is used for the freewheeling purpose, then it is connected in reverse bias.