The mobility of free electrons is greater then that of free holes because

Options

A. they carry negative charge
B. they are light
C. they mutually collide less
D. they require low energy to continue their motion

Answer

To solve the question regarding why the mobility of free electrons is greater than that of free holes, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Free Electrons and Free Holes**:
- Free electrons are negatively charged particles that are found in the conduction band of a semiconductor.
- Free holes are the absence of electrons in the valence band, which can be thought of as positively charged carriers.

2. **Energy Bands**:
- In a semiconductor, there are two main energy bands: the conduction band (higher energy) and the valence band (lower energy).
- The energy gap (Eg) exists between these two bands.

3. **Mobility Definition**:
- Mobility refers to how quickly charge carriers (electrons or holes) can move through a semiconductor when an electric field is applied.
- It is influenced by how easily these carriers can gain energy and move.

4. **Energy Requirements**:
- Free electrons in the conduction band require relatively low energy to continue their motion. They are already in a higher energy state and can move freely with minimal resistance.
- In contrast, free holes in the valence band need to gain energy to move to the conduction band before they can contribute to conduction. This additional energy requirement means that their mobility is lower.

5. **Conclusion**:
- Therefore, the mobility of free electrons is greater than that of free holes because free electrons require less energy to maintain their motion compared to free holes, which must first transition from the valence band to the conduction band.

### Final Answer:
The mobility of free electrons is greater than that of free holes because free electrons are found in the conduction band and require lower energy to continue their motion compared to free holes, which are in the valence band.