Pure silicon has to be doped to make a p-type semiconductor. The impurity atom will be
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Indium
A p-type semiconductor is made by doping silicon (group 14, four valence electrons) with a trivalent impurity (group 13). Each impurity atom has one electron too few to complete the four covalent bonds, so it creates a hole; such an impurity is called an acceptor.
Indium is trivalent (like boron, aluminium and gallium), so it produces a p-type semiconductor.
NCERT (2026-27):
Extrinsic Semiconductor – “… (ii) Trivalent (valency 3); like Indium (In), Boron (B), Aluminium (Al), etc.”
p-type Semiconductor – “This is obtained when Si or Ge is doped with a trivalent impurity like Al, B, In, etc. The dopant has one valence electron less than Si or Ge and, therefore, this atom can form covalent bonds with neighbouring three Si atoms but does not have any electron to offer to the fourth Si atom.”