Question

What is Zener and avalanche breakdown?

Answer 1

**Zener Breakdown** and **Avalanche Breakdown** are two types of breakdown mechanisms that occur in semiconductor devices like diodes when they are exposed to high reverse voltage. Here's an easy-to-understand breakdown of both:

### **Zener Breakdown:**

- **Occurs at lower reverse voltages** (typically below 5-6 volts).
- Happens due to **quantum tunneling**.
- When the reverse voltage increases, the electric field at the junction becomes very strong, and electrons in the semiconductor **tunnel** through the depletion region, which causes a sudden increase in current.
- It is often seen in **Zener diodes**, which are designed to operate in this breakdown region to maintain a **constant voltage** across them.
- **Zener breakdown** is usually **non-destructive** if the current is limited, and it’s often used in voltage regulation applications.

### **Avalanche Breakdown:**

- **Occurs at higher reverse voltages** (typically above 5-6 volts).
- Happens due to **high-energy electrons** colliding with atoms in the semiconductor, creating more electrons and holes (electron-hole pairs).
- As the reverse voltage increases, these secondary electrons accelerate and cause even more electron-hole pairs, leading to a **chain reaction**.
- This breakdown results from the **avalanche effect**, where the current increases sharply.
- **Avalanche breakdown** is typically seen in **avalanche diodes** and **transistors**. Unlike Zener breakdown, this breakdown can be **destructive** if the current is not controlled.

### Key Differences:
1. **Voltage Range:**
   - Zener breakdown: Occurs at **lower** reverse voltages (under 5-6V).
   - Avalanche breakdown: Occurs at **higher** reverse voltages (above 5-6V).
   
2. **Cause:**
   - Zener breakdown: Caused by **quantum tunneling**.
   - Avalanche breakdown: Caused by **high-energy collisions** and the **avalanche effect**.

3. **Applications:**
   - Zener diodes use **Zener breakdown** for **voltage regulation**.
   - Avalanche breakdown is used in **avalanche diodes** and high-voltage applications.

In both cases, breakdown results in a large increase in current, but the physical mechanisms and the voltage levels at which they occur are different.