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Biasing of p–n Junction | Forward and Reverse-biased |

Biasing the p-n junction means applying some external voltage to both sides of the p-n junction. Reverse-biased junction and forward-biased junction are two types of biased junction. You should have also good understanding of  N-Type and P-Type Semiconductor before moving towards this topic.

Introduction Biasing of p–n Junction

Biasing of p–n Junction 

Biasing of a p–n junction means uses of some external voltage across the two sides of the p–n
junction. It is divided into two groups 

  1. Forward-biased junction : When the p-side of junction  is connected to the positive terminal of a battery and the n-side of junction is connected to the negative terminal, the p–n junction is said to be a forward-biased junction. 
  2. Reverse-biased junction :If the positive terminal of the battery is connected to the n-side of junction and the negative terminal on the p-side, the p–n junction is said to be a reverse-biased junction.
Now we will see about forward and reverse-biased junction in detail. 


A forward-biased p–n junction

Given figure below shows that the p-side is connected to the positive terminal and the n-side is connected to the negative terminal of a battery .Holes on the p-side are positively charged and the electrons on the n-side are negatively charged.

Forward-biased p–n junction diagram
Forward-biased p–n junction diagram
                                        

  • When forward biased, the positive terminal of the battery will repel the holes from the terminal.
  • Similarly, the electrons on the n side will be repelled from the negative terminal of the battery.
  • As a result, the width of the depletion layer will be reduced. The potential barrier will also get reduced.
  • If the applied voltage is gradually increased, the depletion region and resistor capacitance will disappear. 

A reverse-biased p–n junction

As we know In reverse reverse-biased p–n junction, connection  of  battery is reversed, i.e., the negative terminal of the battery is connected to the p-side and the positive terminal is connected to the n-side of the p–n junction as shown in given figure below :

reverse-biased p–n junction diagram
Reverse-biased p–n junction diagram
 
  • In a reverse-biased p–n junction the electrons on the n-side are attracted to the positive terminal of the battery and the holes on the p-side are attracted to the negative terminal of the battery.
  • In a reverse-biased p–n junction the holes on the p-side are attracted to the negative terminal of battery and the electrons on the n-side are attracted to the positive terminal of the battery.
  • Furthermore, the depletion layer widens as the applied voltage gradually increases.
  • Barrier is reduced to zero because the barrier voltage also gets gradually increased and as such the possibility of the majority charge carriers crossing the barrier.
  • Due to minority charge carriers a negligibly small current of the order of micro amperes will flow that is shown in given figure.
         

From Biasing of p–n Junction we can make the following statements.

Summary of this topic can be memorized by the following statements given below:

  1. A p–n junction is forward biased if its p-side is connected to the positive terminal of the supply and n-side is connected to the negative terminal of the supply.
  2. Barrier potential for germanium is 0.3 V and for silicon is 0.7 V at room temperature. These are the voltage drops across the p–n junction when current flows.
  3. The majority charge carriers current is established in a forward-biased p–n junction.
  4. When p-side is connected to the negative terminal and n-side is connected to the positive terminal of the supply, the p–n junction is said to be reverse biased.
  5. The depletion layer width gets narrowed down on application of forward voltage. 
  6. The width of the depletion layer, and hence the barrier potential increases when the junction is reverse biased.
  7. A forward-biased p–n junction offers very small resistance to current fl ow while a reverse biased p–n junction offers very high resistance to current flow.
  8. A minutely small current flows through a reverse-biased p–n junction due to the minority charge carriers.

Conclusion 

This information about biasing of p–n Junction, biasing of  forward p-n junction and biasing of reverse-biased p-n junction will help you to enhance your knowledge. If you have any question related to this topic then you can comment us.

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