Explain the concept of the hole in the semiconductor.

(N/A) At absolute zero temperature,each of the valence electrons of a semiconductor is bound by a covalent bond. As a consequence,it behaves as an insulator.
The atoms of the crystal perform thermal oscillations at room temperature. This results in the breaking of several covalent bonds and results in electrons freeing themselves from the covalent bond. These free electrons are responsible for electrical conduction.
Hence,thermal energy ionizes atoms in the crystalline lattice and creates a vacancy in the bond as shown in the figure.
The figure shows a schematic model of the generation of a hole at site $1$ and a conduction electron due to thermal energy at a moderate temperature.
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 an effective positive charge. Although the hole does not really have any electrical charge,it 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 charge carriers.
In intrinsic semiconductors,the number of free electrons,$n_{e}$,is equal to the number of holes,$n_{h}$. That is,
$\therefore n_{e} = n_{h} = n_{i}$
where $n_{i}$ is called the intrinsic carrier concentration.