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

As temperature increases, more electrons gain enough thermal energy to excite to the conduction band, thereby increasing the number of free charge carriers available for conduction. This leads to an increase in the material's conductivity, as more electrons can move freely through the material. Consequently, the resistance of the material decreases.

This phenomenon is observed in semiconductors, where the conductivity significantly improves with temperature. In conductors, however, the increase in temperature typically causes the atoms to vibrate more, which leads to an increase in scattering of the free electrons, thereby increasing the resistance.

The relationship between conductivity and temperature is especially important in devices like thermistors, where the resistance changes significantly with temperature. Positive temperature coefficient (PTC) thermistors show an increase in resistance with temperature, while negative temperature coefficient (NTC) thermistors exhibit the opposite behavior, which makes them useful for temperature sensing and circuit protection applications.

In summary, for most semiconductors, as temperature rises, the number of charge carriers increases, which lowers the resistance, making these materials more conductive. However, in metals and conductors, increased temperature leads to higher resistance due to increased atomic vibrations.