Which of the following elements can be used to dope intrinsic Ge to make it a p-type semiconductor?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → In
A p-type semiconductor is made by doping with a trivalent element (group 13), whose atom has one electron fewer than needed for the four covalent bonds of germanium and so creates a hole (an acceptor).
Indium (In) is trivalent, so it gives 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.”