Question

What are forward biasing and reverse biasing in \( p\text{-}n \) junction? Explain the difference between forward current and reverse current.

Hint:

In practical applications, forward biasing allows current flow in diodes, while reverse biasing is used for blocking and sensing applications.

Answer 1

Step 1: Forward Biasing In forward biasing, the external voltage applied reduces the potential barrier of the depletion region, allowing current to flow easily through the junction.

• The positive terminal of the battery is connected to the \( p \)-side, and the negative terminal to the \( n \)-side.
• As the barrier potential decreases, more charge carriers (electrons and holes) cross the junction.
• The current increases exponentially with applied voltage.

Example: Forward biasing is used in rectifiers and LEDs. Current in forward bias } \[ \boxed{\text{Forward bias allows current flow.}} \] 

 

Step 2: Reverse Biasing In reverse biasing, the external voltage increases the potential barrier, preventing the flow of majority carriers and widening the depletion region.

• The positive terminal is connected to the \( n \)-side, and the negative terminal to the \( p \)-side.
• Only a small leakage current flows due to minority carriers.
• Beyond a certain voltage, breakdown occurs, causing a large current to flow.

Example: Reverse biasing is used in Zener diodes and photodiodes. \[ \text{Reverse current } I_R \approx 0 \] \[ \boxed{\text{Reverse bias restricts current flow.}} \] 

Step 3: Difference Between Forward and Reverse Current