GATE 2019 EC – Question 18
Which one of the following options describes correctly the equilibrium band diagram at T=300 K of a Silicon $pnn^+p^{++}$ configuration shown in the figure?
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Correct answer: (A) Band diagram (A)
Explanation
In equilibrium the Fermi level is flat across the structure. Moving from $p$ to $n$, $n^+$ and $p^{++}$, the conduction band edge is closest to $E_F$ in the $n^+$ region and $E_F$ drops into the valence band in the heavily doped $p^{++}$ region, with a step at each junction. Diagram (A) is the one with a flat $E_F$ and these relative positions.