Main Question or Discussion Point
why do electric field is zero out side of depletion region?
the remaining atom dont generate any fied, then who cancel the field of depletion layer?The remaining atoms have a charge as well. There is nothing "uncovered". A doped semiconductor has free charges of one type with zero overall charge density. If you remove those free charges the volume gets charged.
Sure they do.the remaining atom dont generate any fied
sheets of uniform charge must have infinite dimension(infinite plane) to lead uniform fieldsDistance does not matter in a one-dimensional problem. Sheets of uniform charge density lead to uniform fields in all space (outside those sheets).
i dont talk about approximationCompare the typical thickness of a depletion region with the typical dimension of a semiconductor device.
The infinite sheet is a good approximation unless you consider modern microprocessors, and then things are much more complicated anyway.