Avalanche breakdown is due to

Options

A. shift of fermi level
B. curmulative effect of conductor band electron collision
C. widening of forbidden gap
D. Low impurity concentration

Answer

**Step-by-Step Solution:**

1. **Understanding Avalanche Breakdown:**
- Avalanche breakdown occurs in a p-n junction diode when it is reverse-biased. In this configuration, the p-side is connected to a lower potential and the n-side to a higher potential.

2. **Effect of Reverse Bias:**
- When reverse bias is applied, the depletion region at the junction widens. This means that the majority charge carriers (holes in the p-side and electrons in the n-side) cannot cross the junction.

3. **Minority Charge Carriers:**
- In the p-side, the minority charge carriers are electrons, while in the n-side, the minority charge carriers are holes. Under reverse bias, these minority carriers can still move across the junction.

4. **Electric Field Direction:**
- The electric field in the junction is directed from the n-side to the p-side. This field causes the minority electrons in the p-side to accelerate towards the junction.

5. **Collisions and Energy Transfer:**
- As these electrons gain energy from the electric field, they move with high velocity and can collide with the atoms in the junction. Each collision can free additional electrons, leading to further ionization.

6. **Cumulative Effect:**
- This process of collisions and subsequent ionization leads to a cumulative effect, where a single electron can cause multiple collisions, resulting in a large number of charge carriers being generated.

7. **Current Flow:**
- As a result of this avalanche of charge carriers, a significant current flows in the reverse direction, which is a characteristic of avalanche breakdown.

8. **Conclusion:**
- Therefore, avalanche breakdown is primarily due to the cumulative effect of conduction band electron collisions in the semiconductor material.

**Correct Option:**
- The correct option is 2, which states that avalanche breakdown is due to the cumulative effect of conduction band electron collisions.

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