What are the applications of semiconductor devices

The band gaps of an insulator, semiconductor and conductor are respectively ${\mathrm{E}}_{{\mathrm{g}}_1,} {\mathrm{E}}_{{\mathrm{g}}_2} \mathrm{and} {\mathrm{E}}_{{\mathrm{g}}_3}$.The relationship between them can be given as:

On the basis of band theory, distinguish among insulator, semiconductor, and conductor of electricity.

State anyone difference between the energy band diagram of conductors and that of insulators.

Give an example of semi-conductor.