How does the conductivity of a semiconductor change if its temperature is raised ?

Answer

**Step-by-Step Solution:**

1. **Understanding the Structure of Semiconductors**:
- Semiconductors have a band structure consisting of a valence band and a conduction band. The valence band is filled with electrons, while the conduction band is where electrons can move freely and contribute to electrical conductivity. The energy gap between these two bands is known as the band gap.

2. **Effect of Temperature on Electrons**:
- When the temperature of a semiconductor is raised, the thermal energy of the electrons in the valence band increases. This increase in thermal energy is crucial as it affects the ability of electrons to transition from the valence band to the conduction band.

3. **Electron Transition**:
- As the temperature rises, some electrons in the valence band gain enough thermal energy to overcome the band gap and jump into the conduction band. This transition is essential for conductivity because electrons in the conduction band can move freely and carry electric current.

4. **Increase in Conductivity**:
- With more electrons in the conduction band due to the thermal excitation from the valence band, the overall conductivity of the semiconductor increases. This means that the semiconductor becomes better at conducting electricity as the temperature rises.

5. **Conclusion**:
- Therefore, the conductivity of a semiconductor increases with an increase in temperature due to the excitation of electrons from the valence band to the conduction band.

---