In an intrinsic semiconductor, thermal energy keeps producing electron-hole pairs. At the same time, recombination of charge carriers takes place. Recombination occurs when
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → an electron collides with a hole
Recombination is the reverse of generation. A free electron fills an empty bond, and the electron and the hole both disappear.
Option (1) two holes meet each other — Incorrect. Two holes are two empty bonds. Their meeting fills no bond, so no carrier is lost.
Option (2) an electron collides with a hole — Correct. The free electron drops into the empty bond. The electron-hole pair is lost.
Option (3) a free electron collides with a silicon ion core — Incorrect. Such a collision only scatters the electron. It fills no empty bond, so no pair is lost.
Option (4) a hole reaches the surface of the crystal — Incorrect. A hole is an empty bond inside the crystal. It moves from bond to bond and does not leave the crystal.
NCERT (2026-27):
Intrinsic Semiconductor – “… a simultaneous process of recombination occurs in which the electrons recombine with the holes. At equilibrium, the rate of generation is equal to the rate of recombination of charge carriers. The recombination occurs due to an electron colliding with a hole.”