Semiconductors are the material that has electrical conductivity between insulator and metal.
There are two types of semiconductors are
a) Intrinsic Semiconductors- It is also called pure semiconductors as it does not have any impurity.
b) Extrinsic semiconductors- It is impure semiconductors. In this additional charge carrier either electrons or holes are added to pure semiconductors. This process is called doping. Pure semiconductors are of no use as there are few charge carriers for the conduction process. It is further classified as
I. N- type semiconductors-In this there are large no of electrons are present in the conduction band and less no of holes are present in valence band. So electrons are called majority charge carrier and holes are called minority charge carrier.
e.g. A pentavalent impurity such as phosphorous or arsenic is mixed with the silicon atoms.These are also called donor impurities.
II. P-type semiconductors-The number of holes in the valence band is greater than the number of electrons in the conduction band. So holes are majority charge carrier and electrons are minority charge carrier. e.g. A trivalent impurity such as Boron is mixed with the silicon atoms. These are also called acceptor impurities.