PN junction and space charge region formation

[taekcool]

PN Junction

I understand why depletion zone forms when P and N and put together.
However, I do not understand the real root cause of space charge region formation (depletion zone with charges).

Firstable, I thought depletion zone is an area where holes and electrons and all recombined and they impede from conducting (no voltage bias). So the idea that there are charges inside this depletion region.. I am having hard time buying this. I am more convinced that it's caused by capacitive charging by charges next to depletion zones. But wikipedia says it's caused because when electrons (from donors) diffuse from the N region to P region, they leave behind a POSITIVE DONOR (thus a charge region) and vice-versa for acceptors..... But aren't donors electrically negative from the start? aren't acceptors electrically positive from the start? If that's correct, once they give up their electron or hole... what's left behind is neutral atom not.. a charge.

 

[WimRFP]

PN Junction

Hello,

From the beginning, both N and P material is electrically neutral. The dopants are also neutral atoms. However when in N-material an electrons gains sufficient energy to go to a neighbor, the dopant becomes positive charged (the number of protons do not change) and the neighbor becomes negatively charged, but the net charge of the material remains zero.

When you put them together, the diffusion process starts. When electrons flow from N to P, there is a net charge flow.

The N material becomes positively charges because of the protons in the molecules stay behind. The P-material becomes negatively charged. The resultant field strength in the PN junction will in the end stop the net charge flow.