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Asked in GUJCET 2020 · Depletion region and barrier potential
Idea: the depletion layer is the region the majority carriers have left, and its width sets itself so that the uncovered ions can support the net voltage across the junction.
The built-in barrier V₀ opposes diffusion. A forward bias V is applied with the p side positive, so it acts against V₀ and the net junction voltage falls to V₀ - V.
A smaller junction voltage needs less uncovered charge to support it, so the layer becomes thinner and the field inside it weaker.
More carriers can then diffuse across, which is exactly why the forward current grows so steeply.
So the thickness of the depletion layer decreases.
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