When an electric field is applied across a semiconductor,

Options

A. electrons move from lower energy level to higher energy level in the conduction band
B. electrons move from higher energy level to lower energy level in the conduction band
C. holes in the valence band move from higher energy level to lower energy level
D. holes in the valence band move from lower energy level to higher energy level

Answer

To solve the question regarding the behavior of electrons and holes in a semiconductor when an electric field is applied, we can break down the process step by step.

### Step-by-Step Solution:

1. **Understanding the Energy Bands**:
- In a semiconductor, there are two main energy bands: the **valence band** (lower energy) and the **conduction band** (higher energy). The energy gap between these two bands is called the **band gap (Eg)**.
- The conduction band is typically empty at absolute zero temperature, while the valence band is filled with electrons.

**Hint**: Remember that electrons in the valence band have lower energy compared to those in the conduction band.

2. **Applying Electric Field**:
- When an electric field is applied across the semiconductor, it creates a potential difference. The side of the semiconductor connected to the positive terminal becomes positively charged, while the side connected to the negative terminal becomes negatively charged.

**Hint**: Visualize the electric field direction; it moves from the positive to the negative terminal.

3. **Movement of Electrons**:
- The electrons in the valence band gain energy from the electric field and can jump to the conduction band. This movement is from a **lower energy level (valence band)** to a **higher energy level (conduction band)**.

**Hint**: Think of this as electrons "climbing" from a lower hill (valence band) to a higher hill (conduction band).

4. **Movement of Holes**:
- Holes, which are the absence of electrons in the valence band, behave as positive charge carriers. When electrons move to the conduction band, they leave behind holes in the valence band. The holes can be thought of as moving in the opposite direction of the electrons. Thus, holes move from **higher energy levels to lower energy levels** within the valence band.

**Hint**: Holes move in the opposite direction to electrons; visualize them as "falling" into the gaps left by the electrons.

5. **Analyzing the Options**:
- Now, we can analyze the options provided in the question:
- **Option 1**: Electrons move from lower energy level to higher energy level in the conduction band. **(True)**
- **Option 2**: Electrons move from higher energy level to lower energy level. **(False)**
- **Option 3**: Holes in the valence band move from higher energy level to lower energy level. **(True)**
- **Option 4**: Holes in the valence band move from lower energy level to higher energy level. **(False)**

**Hint**: Check each statement against the behavior of electrons and holes as described.

### Final Answer:
The correct options are **Option 1 and Option 3**.