The conductivity of semiconductors like silicon or germanium can be increased by adding certain amount of impurity or foreign particles in it, this is called doping. The doping can be done either by adding electron rich compound (Example phosphorus) or electron deficit compound (example boron etc). The doped semiconductors are called extrinsic semiconductors and has conductivity greater than pure semiconductor called intrinsic semiconductors. This impurities causes electronic effect in them. When doped with electron rich compound, an unpaired electron becomes delocalized. These delocalized electrons increases the conductivity of doped silicon due to negatively charged electrons when placed in electric field. Silicon doped with electron rich impurity is called n type semiconductor. Similarly when silicon is doped with electron deficit impurity, a delocalized hole is generated with acts as positive charge ion as increases conductivity of silicon when placed in electric field. Silicon doped with electron deficit impurity is called p type semiconductor.