Question

The effect of increase in temperature on the number of electrons in conduction band $\left( n _{ e }\right)$ and resistance of a semiconductor will be as:

• A. $n _{ e }$ decreases, resistance increases
• B. Both $n _{ e }$ and resistance increase
• C. $n _{ e }$ increases, resistance decreases
• D. Both $n_e$ and resistance decrease

Hint:

In semiconductors, increasing the temperature causes an increase in the number of charge carriers, thus reducing resistance.

Answer 1

The Correct Option is C

To understand the effect of temperature on a semiconductor's properties, we should first consider how temperature impacts both the charge carriers and resistance within a semiconductor:

1. Increase in Temperature and its Effect on Charge Carriers:
   • In semiconductors, an increase in temperature excites more electrons from the valence band into the conduction band, as thermal energy overcomes the energy gap.
   • This results in an increase in the number of electrons in the conduction band, denoted as n_e.
   • The increase in n_e means there are more charge carriers available to conduct electricity.
2. Effect on Resistance:
   • The resistance of a material is inversely proportional to the number of free charge carriers.
   • As the number of charge carriers increases with temperature, the resistance of the semiconductor decreases.
   • This phenomenon is opposite to how metals behave, where resistance typically increases with temperature.

Therefore, based on the above explanation, the correct answer is that when the temperature increases, n_e increases and the resistance decreases. This corresponds to the option:

$n _{ e }$ increases, resistance decreases