Question

Why conductivity of conductor decreases while semiconductor increases with increasing temperature?

Answer 1

Hint: When temperature is increased the electrons get more energy. The conductivity of a material depends on the number of charged electrons.

Complete step by step solution:
When temperature is increased in case of a semiconductor the free electron gets more energy to cross the energy gap to the conduction band from the valence band.so now more electrons can go easily to the conduction band so resistance decreases with temperature. But due to temperature increase, in conductors the atoms of the conductor vibrate which gives a resistance to the free electrons. There are two things that affect the resistance. The number of mobile charge carriers (typically electrons or holes) and their mobility (mainly limited due to scattering from atoms).

Conductivity of a material depends on two factors
Number, of electron in conduction band
 Collision of conduction electron with core atom. Factor 1 increases conductivity and Factor 2 decreases.

Additional information:
The big difference between the two materials is the band gap of the semiconductor. Electrons in the semiconductor that do not have sufficient energy cannot contribute to the conductivity. Therefore, increasing the energy of the electrons, increases the number of electrons or holes (charge carriers) that can contribute to the conductivity, thereby drastically lowering the resistance. This effect does not occur in metals.

Note: Because the latter effect is typically much bigger than the first, even though there is an increase of scattering at higher temperatures, the resistance of semiconductors decreases with increasing temperature. When you increase the temperature both the electrons and the atoms will obtain more energy. This holds for both a regular metallic conductor and for a semiconductor. Both materials will see an increase in scattering of electrons from the increasingly vibrating atoms.