Carbon, silicon and germanium have four valence electrons each. Their valence and conduction bands are separated by energy gap \( E_g \). If we represent \( E_{g(c)} \), \( E_{g(si)} \) and \( E_{g(ge)} \) as their respective energy gaps, then which of the following is true
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → \( (E_g)_c \gt (E_g)_{si} \gt (E_g)_{ge} \)
The three elements have the same crystal structure but their atoms differ in size, so the energy gap between the valence and conduction bands decreases as the atoms get larger: carbon (diamond) has the largest gap, then silicon, then germanium.
\( \displaystyle E_g(\mathrm{C}) \approx 5.4\,\mathrm{eV} \qquad E_g(\mathrm{Si}) \approx 1.1\,\mathrm{eV} \qquad E_g(\mathrm{Ge}) \approx 0.67\,\mathrm{eV} \)
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.”