Question

Explain the working method of p-n junction diode in reverse bias with the help of a circuit diagram.

Hint:

In reverse bias, the diode does not conduct current under normal conditions, except for a small leakage current due to minority carriers. The current increases rapidly only when the breakdown voltage is reached.

Answer 1

Reverse Bias Condition: A p-n junction diode is formed by joining a p-type semiconductor and an n-type semiconductor. In reverse bias, the positive terminal of the external battery is connected to the n-type side, and the negative terminal is connected to the p-type side. This configuration increases the width of the depletion region, which prevents current from flowing under normal conditions. The key points of its working are: 1. Reverse Bias Condition: When a p-n junction diode is reverse biased, the applied voltage causes the electrons in the n-region to be attracted to the positive terminal of the battery, while the holes in the p-region are attracted towards the negative terminal. This increases the width of the depletion region, making it difficult for current to flow. 2. Depletion Region: The depletion region acts as an insulator and prevents the current from flowing. In ideal conditions, no current flows in reverse bias, but a small reverse saturation current exists due to minority carriers. 3. Breakdown: If the reverse voltage exceeds a certain threshold (the breakdown voltage), the diode undergoes avalanche breakdown or Zener breakdown, where the depletion region is destroyed, allowing a large current to flow through the diode. This is undesirable in most applications but can be used in Zener diodes for voltage regulation.