Question

The process named ‘minority carrier injection’ in a p-n junction diode occurs during :

• A. forward biasing
• B. reverse biasing
• C. no biasing at low temperature
• D. no biasing at high temperature

Hint:

Remember: - Forward Bias: Lowers the potential barrier \(\rightarrow\) Causes majority carriers to cross over \(\rightarrow\) Leads to Minority Carrier Injection. - Reverse Bias: Heightens the potential barrier \(\rightarrow\) Stops diffusion \(\rightarrow\) Only allows a tiny drift current from existing minority carriers.

Answer 1

The Correct Option is A

Concept: A p-n junction consists of a p-type region (where holes are majority carriers and electrons are minority carriers) and an n-type region (where electrons are majority carriers and holes are minority carriers).
• Built-in Potential: In equilibrium, a depletion region forms creating an internal barrier potential that opposes the further diffusion of majority carriers across the interface.
• Biasing Effects: Applying an external voltage changes this barrier height, altering carrier diffusion across the junction.

Step 1: Explaining the mechanism during Forward Biasing.
When a p-n junction diode is forward-biased (positive terminal of the battery connected to the p-side and negative terminal to the n-side), the externally applied electric field opposes the internal built-in potential barrier. This significantly lowers the barrier height. With the barrier lowered, a large number of majority carriers gain enough energy to cross the junction:
• Electrons from the n-side diffuse across the depletion layer into the p-side region.
• Holes from the p-side diffuse across the depletion layer into the n-side region.

Step 2: Defining Minority Carrier Injection.
Once these diffusing carriers cross the boundary:
• Electrons (majority carriers on the n-side) enter the p-side, where electrons are naturally the minority carriers.
• Holes (majority carriers on the p-side) enter the n-side, where holes are naturally the minority carriers. This flood of majority carriers crossing over and becoming minority carriers near the edges of the opposite regions is called minority carrier injection. This process happens exclusively during forward biasing when the potential barrier is lowered, enabling high diffusion currents. Therefore, this phenomenon matches Option (A).