Regarding diffusion in p-n Junction

Question

I know that in p-n junction there is p type semiconductor in one side where there are majority holes and n-type semiconductor in another side where the majority charge carriers are electrons. Now during diffusion, electrons move from n-type to p-type and holes from p-type to n-type. My argument is I admit that since atom loses electron it becomes immovable positively charged ion and creates a region of positively charged ion in the near side of n type semiconductor. But it is found that nearby p-type semiconductor region of negative ions accumulate creating barrier voltage. I am confused how can there be region of negatively charged ions near p-type semiconductor as holes(positively charged) get neutralized by the electron. Please help.

Answer 1

Electrons of the conduction band of n side of the joint can lower its energy by migrating to the p-side, where there are available states (holes) in the valence band, with lower energy.

But the existence of that available states doesn't mean that p-side of the joint was positive charged. It was neutral before the electron migration.

After the migration, there is an excess of electrons at the p-side of the joint and a lack of electrons at the n-side.

So, there is an electrical field that balances the band structure tendency to migrating. When that E-field is strong enough, the migrating process is no more energetically favorable and the process stops, leaving what is called a depletion zone.