There's one (well, probably more, but right now I'm hung up on this one) aspect of P-N junction diodes that doesn't quite make sense to me.
I understand that doping introduces free electrons in the N-doped region and holes (or empty orbitals?) in the P-doped region, and that because of the density gradient, the free electrons will cross the junction, creating anions in on one side of the depletion zone. Those free electrons will then "fall" into the holes in the P-doped region, creating cations in the other side of the depletion zone, and that because these anions and cations are fixed in the lattice, an electric field will build up that will, at equilibrium, exactly equal the diffusion force.
But here's what's throwing me - in almost every explanation I read, they reference the holes diffusing as well and try as I might, I just can't "see" that. I do see the holes disappearing as they are occupied in the P-doped region by diffused electrons, but I can't grasp the idea that the holes are also moving across the junction to the N-doped region, effectively neutralizing the free electrons. There is one site that I've found that does not refer to hole diffusion in their explanation of the creation of a P-N junction diode, which is the HyperPhysics site hosted by Georgia State University. But since every other explanation I've seen does, I have to ask - are the holes really diffusing as well, or is it really just that cations are forming when the free electrons diffuse, and so we think of that as a hole being created?