Question

Draw the energy-band diagram for conductors, semiconductors, and insulators at T = 0 K. How is an electron-hole pair formed in a semiconductor at room temperature?

Hint:

In semiconductors, at room temperature, the thermal energy excites some electrons from the valence band to the conduction band, leaving behind holes. This forms electron-hole pairs, which contribute to electrical conduction.

Answer 1

At \( T = 0 \, \text{K} \), the energy bands for conductors, semiconductors, and insulators can be described as follows:
- Conductors: In conductors, the conduction band overlaps with the valence band, meaning electrons can freely move in the material, allowing electrical conduction even at absolute zero temperature.
- Semiconductors: In semiconductors, the valence band is completely filled, and there is a small energy gap (band gap) between the valence band and the conduction band. At \( T = 0 \, \text{K} \), no electrons are in the conduction band.
- Insulators: In insulators, the band gap between the valence band and conduction band is large, and electrons cannot move to the conduction band at \( T = 0 \, \text{K} \), preventing conduction. At room temperature (above \( 0 \, \text{K} \)), thermal energy excites some electrons from the valence band to the conduction band, leaving behind holes in the valence band. This creates electron
-hole pairs. These electron
-hole pairs are responsible for electrical conduction in semiconductors. Energy Band Diagram at T = 0 K: \[ \text{Conductors:} \quad \text{No band gap, conduction and valence bands overlap.} \] \[ \text{Semiconductors:} \quad \text{Small band gap, electrons at absolute zero fill the valence band, conduction band is empty.} \] \[ \text{Insulators:} \quad \text{Large band gap, electrons are in the valence band.} \]