Energy bands in Solids : Theory and Concept Illustrations with Solved Problems

Energy bands in Solids

Energy band model

Energy band model is an scheme to describe the conductivity of conductors, insulators, and semiconductors and differentiate them on the basis of energy of electrons of an atom in solids. It provides complete description and behaviour of the conductors, semiconductors and insulators.

Atoms in a crystal interact leading to splitting of energy levels. The amount of interaction is proportion to the atomic spacing. 

Energy band model consists of two energy bands

•     valence band
•    conduction band

And the energy gap between valence band and conduction band is called band gap.
The width of forbidden energy gap between valence band and conduction band distinguishes conductors, semiconductors and insulators from each other.

Important Points:

• The range of energies from the lowest to the highest level of band is called width of a band.
• Energy of inner shell's electrons are split to a lesser degree. 
• Inner shell's electrons energy form a narrow band. 
• Electron from inner shells donot take part in conduction.
• Energy levels of valence electrons are split more and form wider band.
• Electrons start occupying a band from the lowest energy level and fill the levels one after the other in ascending order of energy.
• when all the energy levels are occupied by electrons, the band is said to be full. In the case of non-availability of electrons of electrons, the band gets partly filled.
• when there are no electrons to occupy the energy levels, the energy band remains vacant or empty.