Question

Write any two distinguishing features between conductors, semiconductors and insulators on the basis of energy band diagrams.

Answer 1

Conductors:

(i) In case of conductors, the valence band is completely filled and the conduction band can have two cases-either it is partially filled with an extremely small energy gap between the valence and conduction bands or it is empty, with the two bands overlapping each other as shown below:



(ii) Even when a small current is applied, conductors can conduct electricity.

Insulators :

(i) In case of insulators, the energy gap between the conduction and valence bands is very large and the conduction band is practically empty.



(ii) When an electric field is applied to such kind of material, the electrons find hard to receive such a large amount of energy to attain the conduction band. Thus, the conduction band remains to be empty. That is why no current flows through insulators.

Semiconductors :

(i) In case of semiconductor, the energy band structure is similar to insulator but in this case, the size of forbidden energy gap is quite smaller than that of the insulators.



(ii) When an electric field is applied to a semiconductor, the electrons in the valence band find it relatively easier to jump to the conduction band. So, the conductivity of semiconductors lies between the conductivity of conductors and insulators.