Briefly explain why there are energy bands (and not individual levels) in semiconductors.

Expert Solution

A semiconductor consists of millions and billions of atoms that bond together and form molecules. When valance electrons of two atoms form covalent bonds, they result in two molecular orbitals with slight variation in energy. The lower orbital is called "bonding orbital" and the upper one(with higher energy) is called "antibonding orbital" . Now if N such valence electrons, all of equal energy, are combined to form such bonds, then they will result in N/2 bonding and N/2 antibonding orbitals. But any two such bonding orbital ( or antibonding orbital) can not have exactly same energy due to pauli's exclusion principle.In other words, there will be slight variation in energies amongst the bonding orbitals( or antibonding) also! This give rise to a "band" of energy, i.e there will be a range of energy of these orbitals. The lower band is called valence band and upper one is called conduction band with a slight gap between them called "band gap" separating the two bands.

genius_generous answered 4 months ago

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