On pictures of p-n junctions, what do the circles with positives and negatives inside represent?

The positives have an electron around them, and the negatives have a hole around them.

2012-11-05T11:31:51Z

http://fourier.eng.hmc.edu/e84/lectures/figures/pn_junction0.gif

billrussell422012-11-05T11:30:24Z

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for your first question, I think they represent loose electrons (–) and hole (+).

Re your second statement, make no sense, how can an electron surround anything?

tinkertailorcandlestickmaker2012-11-05T19:40:55Z

My guess would be that the larger circles represent the atoms of the doping element, while the smaller circles are electrons or "holes" (In this case "around" means "in proximity to")