Silicon doped with electron-rich impurity forms ________.
(i) p-type semiconductor
(ii) n-type semiconductor
(iii) intrinsic semiconductor
(iv) insulator
The answer is the option (ii) Silicon has four valence electrons. The conductivity increases on doping with an electron rich impurity as the extra electron becomes delocalised. The increase in conductivity is due to negatively charged electron. That is why silicon doped with electron-rich impurity is called n-type semiconductor.