Match List-I with List-II
| List-I | List-II | ||
|---|---|---|---|
| Semiconductor | Energy gap | ||
| (A) | Germanium | (I) | \( 0.05 \) eV |
| (B) | Silicon | (II) | \( 0.01 \) eV |
| (C) | Germanium doped with Arsenic | (III) | \( 1.1 \) eV |
| (D) | Silicon doped with Arsenic | (IV) | \( 0.72 \) eV |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A) - (IV), (B) - (III), (C) - (II), (D) - (I)
In a pure semiconductor the band gap lifts an electron from the valence band to the conduction band. Arsenic (pentavalent) adds a donor level just below the conduction band, so very little energy frees its fifth electron.
(A) Germanium — this matches (IV) 0.72 eV, the smaller of the two pure band gaps.
(B) Silicon — this matches (III) 1.1 eV, the band gap of pure silicon.
(C) Germanium doped with Arsenic — this matches (II) 0.01 eV, the donor ionisation energy in germanium.
(D) Silicon doped with Arsenic — this matches (I) 0.05 eV, the donor ionisation energy in silicon.
Note: It seems that there is a mistake in the original NTA paper, which heads all four List-II values “Energy gap”; for (C) and (D), 0.01 eV and 0.05 eV are donor ionisation energies, since doping does not change the band gap. The question can still be solved, and Option (3) is the only option that matches them this way.
NCERT (2026-27):
n-type Semiconductor – “… As a result the ionisation energy required to set this electron free is very small and even at room temperature it will be free to move in the lattice of the semiconductor. For example, the energy required is ~ 0.01 eV for germanium, and 0.05 eV for silicon, to separate this electron from its atom. This is in contrast to the energy required to jump the forbidden band (about 0.72 eV for germanium and about 1.1 eV for silicon) at room temperature in the intrinsic semiconductor.”