Question

The resistance of a semiconductor decreases when its temperature increases because:

• A. the number of free charge carriers increases
• B. electron mass decreases
• C. atomic spacing increases
• D. mobility becomes zero

Hint:

Contrast conductors and semiconductors:
In conductors (metals), $n$ is constant, and increasing temperature decreases $\tau$ (more collisions), so resistance increases (positive $\alpha$).
In semiconductors, increasing temperature increases $n$ exponentially, dominating over the change in $\tau$, so resistance decreases (negative $\alpha$).

Answer 1

The Correct Option is A

Step 1: Temperature effect.
Higher temperature excites more electrons to the conduction band, increasing free carrier density and reducing resistance.
Answer: number of free charge carriers increases