Explain the formation of energy bands …
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Posted by यShi Awaस्थी 4 years, 6 months ago
- 2 answers
Gaurav Seth 4 years, 6 months ago
- The solid crystals are formed when the isolated atoms are brought together. Various interactions occur between the neighboring atoms.
- At a particular interatomic spacing d, there is a proper balance between forces of attraction to form a crystal. In this process, the changes occur in the electron energy level configurations.
- In case of a single atom, there is a single energy for an electron orbit.
- However, when two atoms are brought close to each other, it leads to intermixing of electrons in the valence shell.
- As a result, the number of permissible energy levels is formed, which is called an energy band.
- Three bands are important from the conductivity point of view, which are,
- Valence band
- Conduction band
- Forbidden gap or band
- The simple energy band diagram, showing these bands is shown in the figure
- In the normal state, the electrons involved in the covalent bonds in the crystal occupy the valence band and the conduction band is empty. Hence the electrons in the outermost shell are called valence electrons and the outermost shell is called valence shell.
- At higher temperature, these electrons acquire energy and move to the conduction band as electron is not allowed to occupy any energy state in forbidden gap. These electrons are called free electrons.
- For any given type of material the forbidden energy gap may be large, small or nonexistent. The classification of materials as insulators, conductors and semiconductors is mainly dependent on the widths of the forbidden energy gap.
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Mohammad Simraan Ahmad 4 years, 6 months ago
1Thank You