In p-n junction formation, Electron from n-type combine with holes on p-type to form negative ions leaving behind positive ions on n-type. Now, why aren't these negative ions and positive ions attracted by electron on n-type and holes on p-type respectively? They restrict further movement of electrons or holes but why these ions themselves aren't moved with repulsive forces? Both the above factors would've uniformly distributes the negative ions on positive side and positive ions on negative side. But this doesn't happens... why?