Question

Why is there a band gap? Could someone explain how a band gap comes to be/why it occurs?

Answer 1

Solution:

Let us go to the basics first.

Why is there a band gap?

Answer: The band gap is an intrinsic property of all solids. There is a band gap to separate the energy spacing or energy difference between the two types of bands ( the conduction band and the valence band). This gap or region is there to have a space where no electron states can exist (they can only exist in either of the two bands).

How a band gap comes to be/why it occurs?

Answer: Each of the atoms has its own given number of energy levels, or the rings around the nuclei of each of the atoms. These energy levels are positions that electrons can occupy in an atom.

In any solid, there are a vast number of atoms, and hence, a vast number of energy levels. In solids, these atoms are packed tightly with one another, and thus, the energy levels of those atoms will be packed tightly onto one another.

Atoms have a given number of energy levels, however, as an atom has more and more energy levels, the spacing between those energy levels decreases. Thus, the energy levels of an atom are not evenly spaced, but instead, have an unequal spacing that decreases as an atom has more and more energy levels.

There are hundreds of billions of atoms in any solid. All of those energy levels will interact and pack onto one another, forming what are called bands. As the number of energy gaps approaches infinity (which is appropriate to consider in the context of a solid), two important energy bands are formed, the conduction band and the valence band.

When these two types of bands are produced, there is a space (a certain quantity of energy) between these two bands. And thus the band gap occurs.

Thanks!!!