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Asked in GSEB Board July 2018 · Energy bands and band gap
Idea: read the symbols in the order the question gives them -- insulator, semiconductor, conductor -- and then rank the forbidden gaps.
An insulator has the widest gap, about 5.4 eV in diamond, so E_g1 is the largest of the three.
A semiconductor has a narrow gap: 1.1 eV in silicon, 0.72 eV in germanium. That is E_g2, smaller than E_g1 but not zero.
In a conductor the valence and conduction bands overlap, so there is no gap at all to cross and E_g3≈0 is the smallest.
So E_g1 > E_g2 > E_g3.
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