Si doped with aluminium (Al)

The correct answer is Option (2) → Holes

Aluminium is a trivalent impurity, so silicon doped with Al is a p-type semiconductor.

Option (1) Electrons — Incorrect. In p-type Si, the conduction electrons come only from intrinsic generation (bonds broken by heat). Recombination with the many holes reduces them further, so they are the minority carriers.

Option (2) Holes — Correct. Each Al atom leaves a vacancy at its fourth bond and gives one hole. These holes add to the intrinsic holes, so holes are the majority carriers, \( n_h\gg n_e \), and they carry most of the current.

Option (3) Protons — Incorrect. Protons are held inside the nuclei of the atoms, which stay fixed in the lattice, so they cannot move through the crystal.

Option (4) Neutrons — Incorrect. Neutrons carry no charge and stay bound in the nuclei, so they cannot carry a current.

NCERT (2026-27):
Extrinsic Semiconductor – “(ii) p-type semiconductor
This is obtained when Si or Ge is doped with a trivalent impurity like Al, B, In, etc. … It is obvious that one acceptor atom gives one hole. These holes are in addition to the intrinsically generated holes while the source of conduction electrons is only intrinsic generation. Thus, for such a material, the holes are the majority carriers and electrons are minority carriers. Therefore, extrinsic semiconductors doped with trivalent impurity are called p-type semiconductors.”