The conductivity of a semiconductor increases with an increase in temperature, because:
1. number density of free current carries increases
2. relaxation time increases
3. both number density of carries and relaxation time increase
4. number density of current carriers increases, relaxation time decreases but the effect of decrease in relaxation time is much less than the increase in number density
(4) Hint: The conductivity depends on the no. of free current carriers.
The conductivity of a semiconductor increases with an increase in temperature, because the number density of current carries increases, relaxation time decreases but the effect of decrease in relaxation is much less than the increase in number density.