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 band configurations for conductors, semiconductors, and insulators are as follows:
- Conductors: The conduction and valence bands overlap, allowing free electron movement and electrical conduction even at absolute zero.
- Semiconductors: A small energy gap (band gap) exists between the filled valence band and the empty conduction band. No electrons occupy the conduction band at \( T = 0 \, \text{K} \).
- Insulators: A large band gap prevents electrons from reaching the conduction band at \( T = 0 \, \text{K} \), thus inhibiting conduction.At temperatures above \( 0 \, \text{K} \) (e.g., room temperature), thermal energy promotes electrons from the valence band to the conduction band, creating electron-hole pairs and enabling electrical conduction in semiconductors. Energy Band Diagram at T = 0 K:\[\text{Conductors:} \quad \text{Conduction and valence bands overlap; no band gap.}\]\[\text{Semiconductors:} \quad \text{Small band gap; valence band is filled, conduction band is empty.}\]\[\text{Insulators:} \quad \text{Large band gap; electrons reside in the valence band.}\]