To obtain a n-type silicon semiconductor, it must be doped with

The correct answer is Option (2) → Phosphorus

An n-type semiconductor is made by doping silicon (valency 4) with a pentavalent impurity. Four of its valence electrons form covalent bonds with the neighbouring silicon atoms, and the fifth is loosely bound and becomes a free electron. Such an impurity is called a donor.

Option (1) Aluminium — Incorrect. Aluminium is trivalent; it creates holes and gives a p-type semiconductor.

Option (2) Phosphorus — Correct. Phosphorus (group 15) is pentavalent, so each atom donates one free electron.

Option (3) Boron — Incorrect. Boron is trivalent, an acceptor impurity that gives a p-type semiconductor.

Option (4) Magnesium — Incorrect. Magnesium has only two valence electrons; it is not a donor for silicon.

NCERT (2026-27):
Summary – “… 8. n-type semiconducting Si or Ge is obtained by doping with pentavalent atoms (donors) like As, Sb, P, etc., while p-type Si or Ge can be obtained by doping with trivalent atom (acceptors) like B, Al, In etc.”