GATE EC 2023 Set 1 — Question 19
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Question
For a MOS capacitor, and are the flat-band voltage and the threshold voltage, respectively. The variation of the depletion width () for varying gate voltage () is best represented by
Correct answer
(B) [figure]
Solution
In a MOS capacitor, the depletion width () varies with the gate voltage () as follows:
1.Accumulation Region (): In this region, the semiconductor surface accumulates majority carriers. The depletion region collapses, and the depletion width is ideally zero or very small.
2.Depletion Region (): As increases beyond , the semiconductor surface starts to deplete majority carriers, and a depletion region forms. The depletion width increases with increasing in this region.
3.Inversion Region (): Once exceeds the threshold voltage , an inversion layer forms at the surface. The depletion width reaches its maximum value () at and then remains relatively constant even with further increases in because the additional charge is accommodated by the inversion layer, not by further widening the depletion region.
Therefore, the depletion width starts small (near zero) in accumulation, increases as goes from to , and then saturates at its maximum value in inversion.Graph (B) correctly depicts this behavior: is low in accumulation, increases from to , and then flattens out for .The final answer is .Continue learning with Success Tracker
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