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Asked in GSEB Board July 2022 · Energy bands and band gap
Idea: the forbidden gap is the energy an electron in the valence band must gain to enter the conduction band, and it is a property of the material itself.
For silicon at room temperature E_g ≈ 1.1 eV; for germanium it is about 0.7 eV.
Compare that with the average thermal energy at 300 K, which is only about 0.026 eV.
The gap is some forty times larger, so only the rare electron far out in the tail of the energy distribution gets across. That is why a pure semiconductor conducts only slightly, and why heating it helps.
So about 1.1 eV is needed.
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