# Is diffusion of electrons (under Fick law) from N to P side of a PN junction dominated by electrons coming from doped or from non doped atoms ? Why?

Let's consider a PN junction between two semiconductor doped P and N. Let's concentrate on the N side for example. Due to Fick law, the electrons from the N side migrate to the P side.

What is the origin of these electrons that migrate : the N doped atoms or the non doped atoms ? Or both ? Is one source dominant ? If yes, which one, and why ?

Do all additive electrons of the N doped atoms migrate or only a subfraction ?

Do some electrons of non doped atoms migrate also ?

Thank you.

• An electron is an electron- how can you tell where it came from? – Jon Custer Sep 16 '19 at 2:00
• does is come from the non doped atom or from the doped atom ? Or both ? I mean is the liaison energy different for the doped and the non doped atom ? – Mathieu Krisztian Sep 16 '19 at 5:35
• Once an electron is in the conduction band, you have no way of knowing where it came from. And, very few electrons from the n-type are going to make it to the p-type region - the excess of holes pretty much guarantees recombination. – Jon Custer Sep 16 '19 at 17:42
• Sorry you escape the question. I focus on N side. Are electron that migrate from Fick law mainly coming from the doped or the non doped atoms ? – Mathieu Krisztian Sep 17 '19 at 16:18
• Do electron need to be in conduction band to diffuse ? If so since electrons from doped atoms are closer to conduction band I would expect that people say that electrons that diffuse are highly dominated by those coming from the doped atoms with respect to the non doped atoms. ? – Mathieu Krisztian Sep 17 '19 at 16:21