Which of the following causes electric conduction in a semiconductor?

The correct answer is Option (3) → Both electrons and holes

In a semiconductor, an electron that breaks free of its bond moves into the conduction band and leaves behind a vacancy, a hole, in the valence band. Under an electric field the free electrons move one way and the holes, behaving as positive charges, move the other way; both motions carry current in the same direction. The total current is \( I = I_e + I_h \).

Option (1) Holes only — Incorrect. Holes carry only part of the current; the free electrons in the conduction band also conduct.

Option (2) Electrons only — Incorrect. This is true of metals, but in a semiconductor the holes also contribute.

Option (3) Both electrons and holes — Correct. Both electrons and holes are charge carriers in a semiconductor.

Option (4) Neither holes nor electrons — Incorrect. Without charge carriers there would be no conduction at all; a semiconductor does conduct, through electrons and holes.

Note: A similar question was also asked in CUET (UG) 2026 on 29-05-2026 (Slot 2).

NCERT (2026-27):
Intrinsic Semiconductor – “… The free electron moves completely independently as conduction electron and gives rise to an electron current, I_e under an applied electric field. Remember that the motion of hole is only a convenient way of describing the actual motion of bound electrons, whenever there is an empty bond anywhere in the crystal. Under the action of an electric field, these holes move towards negative potential giving the hole current, I_h. The total current, I is thus the sum of the electron current I_e and the hole current I_h:

    \( \displaystyle I = I_e + I_h \qquad (14.2) \) ”