Answer:-

n-type semiconductor: n-type semiconductor contains increased number of electrons in the conduction band. 

When Si semiconductor is doped with 15th group element phosphorus, P, the new atoms occupy some vacant sites in the lattice in place of Si atoms. 

P has five valence electrons, out of which four are involved in covalent bonding with neighboring Si atoms while one electrons remains free and delocalised.  These free electrons increase the electrical conductivity of the semiconductor.  The semiconductors with extra nonbonding free electrons are called n-type semiconductors