Question

In an insulator, the forbidden energy gap between the valence band and conduction band is of the order of

Answer 1

Band theory

1. Every material has a lower energy band termed the valence band, which includes the charge carriers, and electrons, according to band theory.
2. A higher energy band is the conduction band, which has more energy than the valence band. To transmit electricity through a material, electrons from the valence band must be stimulated into the conduction band.
3. There are three classes of materials based on the amount of energy necessary to excite electrons from the valence band to the conduction band. They are conductors, semiconductors, and insulators.

Insulators

1. Insulators are materials with a large energy difference between the valence and conduction bands, often in the order of eV.
2. In insulators, this energy difference is known as the forbidden energy gap (Eg). Its value is around 6eV.
3. For example, a diamond is an insulator with a 5.5eV energy gap.

Hence, in insulators, the forbidden energy gap is the largest and it is of the order of 6 eV approximately.