Which of the following corresponds to an intrinsic semiconductor at \( T = 0\,\mathrm{K} \)?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2)
An intrinsic semiconductor is pure, so its band diagram has no donor or acceptor level in the gap. At \( T = 0\,\mathrm{K} \) there is no thermal energy to lift electrons across the gap, so the valence band is completely filled and the conduction band is completely empty: no free electrons and no holes.
Option (2) shows exactly this: a filled valence band, an empty conduction band and no impurity level.
Why the other options are incorrect
Option (1) — Incorrect. It shows electrons in the conduction band and holes in the valence band; that happens only above 0 K.
Option (3) — Incorrect. It shows a donor level \( E_D \), which belongs to an n-type (extrinsic) semiconductor, and carriers in the bands.
Option (4) — Incorrect. It shows an acceptor level \( E_A \), which belongs to a p-type (extrinsic) semiconductor, and holes in the valence band.
NCERT (2026-27):
Intrinsic Semiconductor – “… An intrinsic semiconductor will behave like an insulator at T = 0 K as shown in Fig. 14.6(a).”
