Question

The conductivity of a semiconductor increases with increase in temperature because

• A. number density of free current carriers increase
• B. relaxation time increases
• C. both number density of carriers and relaxation time
  increase
• D. number density of current carriers increase, relaxation time decreases but effect of decrease in relaxation time is much less than increase in number density

Answer 1

The correct option is A number density of free current carriers increase

In semiconductor, the density of charge carriers (electron holes) are very small, so its resistance is high. $\text{When temperature increases the charge carriers (density) increases which increases the conductivity}$. As temperature of semiconductor increases, the speed of free electrons increases which $\text{decreases the relaxation time}$. As the density of charge carrier is small so there is small effect on decrease of relaxation time.
Option A is correct.