Arrange the following materials in the increasing order of their energy band gaps.
A. Germanium
B. Metal
C. Carbon
D. Silicon
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → B, A, D, C
The energy band gap \( E_g \) separates the filled valence band from the conduction band. In a metal the bands overlap (or the conduction band is partly filled), so \( E_g = 0 \). Carbon here is carbon in its diamond form, the group-IV partner of silicon and germanium, which is an insulator.
(B) Metal: \( E_g = 0 \)
(A) Germanium: \( E_g \approx 0.7\,\mathrm{eV} \)
(D) Silicon: \( E_g \approx 1.1\,\mathrm{eV} \)
(C) Carbon (diamond): \( E_g \approx 5.4\,\mathrm{eV} \)
Increasing order of band gap: B, A, D, C.
NCERT (2026-27):
Extrinsic Semiconductor – “… The difference in the resistivity of C, Si and Ge depends upon the energy gap between their conduction and valence bands. For C (diamond), Si and Ge, the energy gaps are 5.4 eV, 1.1 eV and 0.7 eV, respectively. Sn also is a group IV element but it is a metal because the energy gap in its case is 0 eV.”