GATE EC 2017 Set 2 — Question 39
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Electronic Devices → P-N Junction & Diodes → Junction Formation & Depletion
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Question
An abrupt junction (located at ) is uniformly doped on both and sides. The width of the depletion region is and the electric field variation in the -direction is . Which of the following figures represents the electric field profile near the junction?
Correct answer
(A) Triangular profile, positive: E(x) rises linearly from zero at the n -side depletion edge to a positive peak at x=0 and falls linearly to zero at the p -side edge (total width W; n -side on the left, p -side on the right).
Solution
In the depletion region of a uniformly doped abrupt junction the space charge is on the -side and on the -side. Gauss's law then makes piecewise linear, zero at both depletion edges and largest in magnitude at — a triangle, so the rectangular profiles B and D are wrong.Direction: the field points from the positive donor ions (-side, on the left) to the negative acceptor ions (-side, on the right), i.e. along . So : on the -side it rises from 0 (slope ), on the -side it falls back to 0 (slope ). The negative triangle C would have the field pointing from to .Answer: (A)
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