Question

What is meant by ‘forbidden zone’ in reference to the band theory of solids?

Answer 1

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forbidden zone is the energy gap between valence band and conduction band in solids .this gap is large in insulators and small in semi conductors . there is no forbidden zone in metals because in metals valence and conduction band overlap.

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Answer 2

The gap between the conduction band and the valence band is referred to as the 'forbidden zone ' of the band theory of solids.

Discuss:

• Valence band:

The valence band has the lowest energy band in the solids. It shows the energy band of valence electrons of an atom of a solid.

• Conduction band:

The conduction band has a higher energy band than the valence band. The electrons which have sufficient energy to jump from the valence band will jump to the conduction band and this is the basic region for conduction.

• Forbidden band:

The forbidden band is the band of those energies which do not possess by the electrons of the solid. So no electrons reside in this band.

• The larger the forbidden band, it is hard for an electron to jump the energy gap between the valence band and the conduction band so electrons will be tightly bounded to the valence shell in this case, and their ionizing energy is also more.

Thus, the energy band gap between the valence and the conduction band is called a forbidden zone.

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