Explain with a diagram how current flows due to electrons and holes in a pure semiconductor.

(N/A) Semiconductors have unique properties where holes move in addition to electrons.
Suppose there is a hole at site $1$ as shown in the figure.
An electron from a covalent bond at site $2$ may jump to the vacant site (hole).
Thus,after such a jump,the hole is at site $2$ and site $1$ now has an electron.
Hence,the hole and the electrons move in opposite directions. The free electron moves independently as a conduction electron and gives rise to an electron current,$I_{e}$,under an applied electric field.
$A$ hole is in a covalent bond. It moves from high electric potential to low electric potential under the influence of an external electric field. This motion of holes creates a hole current,$I_{h}$.
Thus,we get two types of currents in semiconductors:
$(1)$ Due to the motion of free electrons.
$(2)$ Due to the motion of holes (the process of jumping electrons into vacant sites).
Hence,in a semiconductor,the total current $I$ is the sum of the electron current $(I_{e})$ and the hole current $(I_{h})$: $I = I_{e} + I_{h}$.