Question

When the temperature of a semiconductor increases then

• A. number of free electrons only increases
• B. number of holes only increases
• C. both number of free electrons and number of holes increase
• D. both number of free electrons and number of holes decrease

Hint:

In semiconductors, charge carriers (free electrons and holes) are generated by thermal excitation. Higher temperatures provide more energy for electrons to jump from the valence band to the conduction band, creating more electron-hole pairs. Thus, an increase in temperature leads to an increase in the concentration of both free electrons and holes.

Answer 1

The Correct Option is C

In a semiconductor material, the electrical conductivity is significantly lower than that of conductors but higher than that of insulators at room temperature.
The conductivity depends on the concentration of charge carriers, which are free electrons and holes.
At temperatures above absolute zero, thermal energy can excite electrons from the valence band to the conduction band, creating free electrons in the conduction band and leaving behind holes in the valence band.
This process is called thermal generation of electron-hole pairs.
When the temperature of a semiconductor increases: - More thermal energy is available to break covalent bonds in the semiconductor lattice.
- This increased energy causes more electrons to be excited from the valence band to the conduction band.
- As a result, the number of free electrons in the conduction band increases.
- Simultaneously, for every electron that moves to the conduction band, a hole is created in the valence band.
- Therefore, the number of holes in the valence band also increases.
The increase in both the number of free electrons and the number of holes leads to an increase in the conductivity of the semiconductor with increasing temperature.
Options (A) and (B) are incorrect because the generation of free electrons and holes occurs in pairs due to thermal excitation.
Option (D) is incorrect because increasing temperature provides more energy for carrier generation, thus increasing their numbers.