Avalanche breakdown in a semi conductor diode occurs when

Options

A. Forward current exceeds a certain value
B. Reverse bias exeeds a certain value
C. Forward bias exceeds a certain value
D. The potential barrier is reduced to zero

Answer

### Step-by-Step Solution:

1. **Understanding Avalanche Breakdown**:
- Avalanche breakdown is a phenomenon that occurs in semiconductor diodes when they are reverse-biased beyond a certain voltage threshold.

2. **Forward and Reverse Bias**:
- In a diode, when the anode (point A) is at a higher potential than the cathode (point B), the diode is said to be in forward bias, allowing current to flow.
- Conversely, when the cathode is at a higher potential than the anode, the diode is in reverse bias, and ideally, no current flows.

3. **Limit of Reverse Bias**:
- While in reverse bias, a diode can withstand a certain amount of reverse voltage without conducting significant current. This is known as the breakdown voltage.

4. **Breakdown Voltage**:
- When the reverse voltage exceeds this breakdown voltage, the diode enters a state where it can conduct a large amount of current. This is known as avalanche breakdown.

5. **Mechanism of Avalanche Breakdown**:
- In avalanche breakdown, the high reverse voltage causes free electrons to gain enough energy to collide with the lattice atoms, creating more electron-hole pairs. This leads to a chain reaction, resulting in a large increase in current.

6. **Conclusion**:
- Therefore, avalanche breakdown in a semiconductor diode occurs when the reverse bias voltage exceeds a certain critical value, leading to a significant increase in current flow.