Question

Explain the origin of a bandgap, and describe how the existence and size of the bandgap
may be used to classify solids into metals, semiconductors and insulators. The answer
should include mention of the Fermi energy and its place in the band structure for each
class of material.

Answer 1

Fermi level is the level up to which the electrons are filled at a temperature zero kelvin.

Band gap is the energy difference between the valence band and conduction band.

For the process of conduction the electrons must be transferred from Valence band to conduction band.

Insulators are the one in which the Fermi level lies completely within the valence band where as conductors are the ones in which the Fermi level lies in the conduction band therefore no energy required to transfer the electrons to conduction band in case of conductors where as a significant amount of energy required to transfer electrons from Valence band to conduction band in case of insulators.