Linked from
The 10 pages that link to Depletion region, each with the reason it gives.
PhotodiodeRelated: Photons absorbed here generate carriers that the field can rapidly separate.
Schottky diodeRelated: Its extent affects the junction’s electric field and capacitance.
Forward biasRelated: The applied polarity narrows this region as the junction conducts.
Junction transistorRelated: Its electric field controls which carriers cross a transistor junction.