If the lattice constant of this semiconductor is decreased, then which of the following is correct? (a) All Ec, Eg, Ev increase (b) Ec and Ev increase, but Eg decreases (c) Ec and Ev decrease, but Eg increases (d) All Ec, Eg, Ev decrease

Answer: (c). In the figure Ec and Ev are the widths of the conduction and valence bands, Eg is the gap between them. Smaller lattice constant means atoms are closer, so their wave functions overlap more. Greater overlap spreads each level over a wider range: Ec and Ev increase. Wider bands come closer to each other, so the gap Eg decreases. This gives (b); the answer key gives (c).

If the lattice constant of this semiconductor is decreased, then… | JEE Main 2006 (AIEEE)

Q17JEE Main 2006 · AIEEEMedium

Energy Bands in Solids

If the lattice constant of this semiconductor is decreased, then which of the following is correct?

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Answer: (c)

In the figure $E_c$ and $E_v$ are the widths of the conduction and valence bands, $E_g$ is the gap between them.
Smaller lattice constant means atoms are closer, so their wave functions overlap more.
Greater overlap spreads each level over a wider range: $E_c$ and $E_v$ increase.
Wider bands come closer to each other, so the gap $E_g$ decreases.
This gives (b); the answer key gives (c).

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