An Energy Band in different electrical materials

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An energy band in a solid is a range of allowed energies for electrons. Electrons can only exist in these energy bands, and they cannot have energies in between. Energy bands are separated by regions of forbidden energies, where electrons cannot exist.

The two most important energy bands in a solid are the valence band and the conduction band. The valence band is the highest energy band that is normally occupied by electrons. The conduction band is the lowest energy band that is normally unoccupied by electrons.

If an electron has enough energy to cross the forbidden energy gap between the valence band and the conduction band, it can become a free electron and contribute to electrical conduction.

The type of electrical material that a solid is depends on the width of its forbidden energy gap.

  • Conductors have a very small or no forbidden energy gap, so electrons can easily move from the valence band to the conduction band and contribute to electrical conduction.

  • Semiconductors have a small forbidden energy gap, so electrons can be excited from the valence band to the conduction band by applying heat or light. This makes semiconductors useful for making electronic devices such as transistors and solar cells.

  • Insulators have a large forbidden energy gap, so it is very difficult for electrons to move from the valence band to the conduction band. This makes insulators useful for preventing electrical conduction.

Here are some examples of materials and their energy band types:

  • Conductors: copper, aluminum, gold

  • Semiconductors: silicon, germanium, gallium arsenide

  • Insulators: diamond, glass, plastic