Practice portal › Semiconductor Electronics › p-n Junction Formation
Asked in GUJCET 2019 · Depletion region and barrier potential
Idea: the space charge region -- the depletion layer -- is the thin layer at the junction that diffusion empties of free carriers, leaving only the bare dopant ions behind.
Its width is set by the doping: the more heavily doped the crystal, the fewer uncovered ions are needed to build the barrier, and the thinner the layer.
For an ordinary p-n junction it works out at the order of 10⁻⁷ to 10⁻⁶ m, that is a few tenths of a micrometre.
Of the four values offered, only 0.5 lies in that range; 5 and 6 are ten times too wide and 0.05 is ten times too thin.
So the space charge region is approximately 0.5 μm wide. Check it against the field: a barrier of a few tenths of a volt across 0.5 μm gives about 10⁶ V m⁻¹, which is the field such a junction really has.
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