How does a p-n junction work?

mike2349

I've been reading various explanations for a number of hours, and I'm still completely confused. I'll refer to an explanation from Wikipedia, but do point me to a better one if you know one.

What does the depletion zone have to do with current flow? Looking at Figure A (see link above), there are plenty of charge carriers throughout the depletion layer, mostly holes on the left and mostly electrons on the right. And they are in equilibrium, so there is no net force stopping them. If a potential difference is applied either way, why won't current flow through the depletion zone like in a normal conductor, with the oncoming electrons filling the oncoming holes?

In case it helps with pinpointing my source of confusion, I have (or should have) roughly high-school-level physics and chemistry knowledge (no such claims about understanding), I visualise free electrons as tiny charged balls that obey Newtonian physics and Coulomb's law and nothing more, and I don't understand how non-ionic chemical bonds work.

willem2

There are no holes or loose electrons in the depletion layer. What you see in figure A, are the negatively charged acceptor atoms, and the positively charged donor atoms, that have created the free electrons and the holes that have diffused to the other side of the junction. The donor/accpetor atoms can't move. The only way of getting the p-n junction to connect is feeding in electrons on the n-side to fill in the positively charged part of the depletion layer, and removing them to create holes to fill in the negatively charged part of the depletion layer.

mike2349

The negatively charged acceptor atoms and the positively charged donor atoms are the circled minuses and pluses, right? But what about the red and blue lines? I thought they show the free electrons and holes, which can move?

willem2

They show the concentration of holes. Note that it's on a logarithmic scale, so the concentration both of holes and electrons at the point where the red and the blue line meets, is very small