Hole in a semiconductor:
In a semi-conductor the energy gap is of the order of 1eV. At OK, the semi-conductor behaves like an insulator but at room temp the electrons acquire sufficient energy to jump to the conductor band thereby creating a vacancy in the valence band.
This deficiency or vacancy of electron in the valence band is termed as a hole. It is equivalent to 1 unit of +Ve charge. To fill this vacancy, the nearly electrons present in the valence band jumps to that position. So another hole is created and thus it appears as if the holes are moving. So, in R semi-conductor, electrons move in the conduction band whereas holes in the valence band.
Why doping is done in semiconductors?
The addition of impurity atoms to a pure-semi-conductor is known as doping. The doping is done to increase the conductivity of a pure semi-conductor. It must be noted that the impurity atom is about 1 in every 1010 atoms.