N type semiconductors are the extrinsic semiconductors doped with an electron rich element.
In this, free electrons are resonsible for conductivity.
A semiconductor ( like Si with a valenciy of 4 ) is doped with an electron rich material like As( Group 15, valency 4).4 electrons are used by As to make covalent bond with the neighbouring Ge atoms and the one extra electron is free to move through the crystal lattice.
eg : Ge doped with As.
P type semiconductor.
This is an extrinsic semiconductor made by doping with an electron deficient molecule.
Eg : Si doped with B
Here, Si has a valency 4 and B has a valency 3. So when some of the Si are replaced by B, Only 3 electrons are available for bonding with the neighbouring atom. So one of the neighbouring bond breaks and the electron come towards the B helping it to make the fourth bond. This creates an electron deficiency at the sight from which the bond was broken. So another bond is broken and electron come to this sight and so on. It would appear that a positive hole is moving in the direction opposite to the diection of flow of elelctrons.Hence it is called a p - tyoe semiconductor.
Hope that helps.
