Which of the energy band diagrams shown in the figure corresponds to that of a semiconductor?

Options

A.
B.
C.
D.

Explanation

To determine which energy band diagram corresponds to a semiconductor, we need to understand the characteristics of energy bands in conductors, semiconductors, and insulators.

### Step-by-Step Solution:

1. **Understand Energy Bands**:
- In solids, electrons occupy energy bands. The two most important bands are the **valence band** (filled with electrons) and the **conduction band** (where electrons can move freely and conduct electricity).

2. **Identify the Characteristics of Each Type of Material**:
- **Insulator**:
- Has a large energy gap (EG) between the valence band and the conduction band.
- The gap is much greater than thermal energy (KT), meaning electrons cannot easily jump from the valence band to the conduction band, resulting in no electrical conductivity.
- **Conductor**:
- The conduction band and valence band overlap or coincide, allowing electrons to flow freely, which results in high conductivity.
- **Semiconductor**:
- Has a small energy gap (EG) between the valence band and the conduction band.
- The gap is comparable to thermal energy (KT), allowing some electrons to jump from the valence band to the conduction band at room temperature, enabling partial conductivity.

3. **Analyze the Given Options**:
- Look at the energy band diagrams provided in the question.
- Identify which diagram shows a small energy gap between the valence band and the conduction band, indicating that it can conduct electricity under certain conditions.

4. **Select the Correct Diagram**:
- Based on the characteristics discussed, the diagram that shows a small energy gap (EG ≈ KT) between the valence band and conduction band corresponds to a semiconductor.
- From the options provided, identify that **option number four** matches this description.

5. **Conclusion**:
- Therefore, the energy band diagram that corresponds to a semiconductor is **option number four**.