Question

Explain the working method of a reverse biased (p-n) junction diode by making its circuit diagram and explain avalanche breakdown with the help of its V-I characteristic graph.

Hint:

Avalanche breakdown is the result of the acceleration of minority carriers due to a high reverse bias, causing a chain reaction of electron-hole pair generation. Always be cautious about exceeding the breakdown voltage of a diode, as it can lead to permanent damage.

Answer 1

Working of a Reverse Bias (p-n) Junction Diode:
A p-n junction diode works by allowing current to flow in only one direction. When the diode is reverse biased, the p-side is connected to the negative terminal, and the n-side is connected to the positive terminal of the battery. This increases the width of the depletion region, and as a result, no current flows under normal conditions.
The current through the diode in reverse bias remains negligibly small (very small leakage current), and the reverse bias voltage increases the width of the depletion region, thereby preventing the flow of majority charge carriers. The diode essentially acts as an insulator.
The reverse bias is applied in such a way that the n-type material (negative side) is connected to the positive terminal of the battery and the p-type material (positive side) is connected to the negative terminal of the battery. This results in a very small reverse current, mainly due to minority charge carriers. Avalanche Breakdown:
Avalanche breakdown occurs when the reverse bias voltage exceeds a critical value. When the reverse bias increases, the minority carriers gain more energy and collide with the atoms of the semiconductor, creating more electron-hole pairs. This process multiplies and results in a large current, which is known as avalanche breakdown. The current increases rapidly with an increase in reverse voltage after the breakdown. V-I Characteristic Graph:
The V-I characteristic graph for a reverse biased diode shows a small leakage current initially. As the reverse voltage increases, the current remains nearly constant until the breakdown voltage is reached. After this point, the current increases rapidly, representing avalanche breakdown. Explanation of the Graph:
- The current remains negligible in the reverse region until the breakdown voltage is reached.
- Once the breakdown voltage is exceeded, the current increases exponentially, signifying avalanche breakdown.