Q:

Charge density in depletion layer for pn-junction

I just came across this Wikipedia article on pn-junctions:
pn junction
What I don't get is why the negative charge density is narrower/smaller than the positive one in Figure A. I'm guessing the area is probably the same, so why don't they just make them the same shape ? Is there a good reason to why they are different, or...?

A:

You can see from the Q over x diagram that the p-doping is stronger than the n-doping. (More aceptors per volume in the p-region than donators per volume in the n-region.)
The overall depletion zone is neutral (e.g., the diode is not electrically charged). Therefore, the overall charge must be zero. The positive charge of the depleted n-region with less donators per volume must be the same as the negative charge of the depleted p-region with more acceptors per volume. Therefore, the space charge region must penetrate the n-region deeper than the p-region.

