(1) n–type doping: In this, element with five valence electrons are added as impurity(pentavalent impurity or donor impurity) in the semiconductor. Semiconductor has four valence electrons, when it is doped with pentavalent impurity the four valence electron makes covalent bond and the remaining one is now free to move, this is how n-type doping increases conductivity of the semiconductor. Due to excess of electron (e) in the n-type semiconductor it generates an overall negative charge and thus the name n-type semiconductor.