P-n junction diode open circuit electric field

[rajasmannam]

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[Okefenokee]

On the n side, dopant donor atoms give free-roaming electrons to the semiconductor. That leaves a stationary positive charge where the dopant atom is. On the p side, dopant acceptor atoms trap electrons and create free roaming holes. That leaves behind a stationary negative charge where the dopant atom is.

A p type or n type by itself will be in equilibrium. The charge of the free roaming charges will balance with the charge of any dopant atom sites. When you create the p-n junction, the free roaming holes on the p side of the junction and the electrons on the n side will find each other and annihilate. This creates a depletion region where charge carriers are less dense but the dopant atoms are still there and they have charge. On the p side the negative dopant sites are exposed and on the n side the positive dopant sites are exposed. A field is created by the stationary dopant atoms.