Explain the concept of the hole in the semiconductor.

Explanation

At absolute zero temperature each of the valence electrons of semiconductor is bound by the covalent bond. As a consequence it behaves as insulator.
The atoms of the crystal perform thermal oscillations at the room temperature. This results in the breaking of several covalent bonds and results in the electrons freeing from the covalent bond. These free electrons are responsible for electrical conduction.
Hence, thermal energy ionize atoms in the crystalline lattice and creates vacancy in the bond as shown in figure (a).

In figure schematic model of generation of hole at site 1 and conduction electron due to thermal energy at moderate temperature is shown.
The neighbourhood from which the free electron with charge -q has come out leaves a vacancy with an effective charge +q.
This vacancy with the effective positive electronic charge is called a hole.
The hole behaves as an apparent free particle with effective positive charge but the hole does not really have any electrical charge but the hole has the property of attracting electrons, so it is assumed to have a + q charge.
In intrinsic semiconductors both the free electrons and the holes are electric charges.
In intrinsic semiconductors, the number of fr electrons, `n_(e )` is equal to the number of holes n
That is,
`therefore n_(e )=n_(h)=n_(i)`
where `n_(i)` is called intrinsic carrier concentration.