Not in wild spirits at T=0K, electrons move on the orbit, next to a kernel. In a solid body atoms the close friend to an electronic cloud shift power are formed the whole zones of levels.
Boundary layer. Will be will be impoverished by charge carriers => there will be internal U. It is U will interfere with diffusive current and it will fall. On the other hand existence of an internal field will cause emergence of dreyfy current of nonbasic carriers. Eventually diffusive current will become = to drift current and total current through transition will be = 0