Ohhh. I have no real knowledge of electricity or electronics, but I know transistors are very fundamental so if you squint a bit, you might say this is what we set in motion when we program, or even just use a computer! Or at least some of it. Not knowing enough to benefit from it I learned nothing, and don't regret a second of that.
You can google for "From nand to tetris" or get the book Digital Design and Computer Architecture by Harris to get the idea of how these machines work.
The simulation does calculations on the fields only, so it keeps track of the average electron and hole density at each point in space. There is, however, a one-to-one correspondence between the behavior of the fields and the motion of individual particles, which is what makes these animations possible. What I mean by this is the diffusion equation is satisfied by the probability density of a particle undergoing a random walk. So given an electron density that obeys the diffusion-drift equations we can make dots undergo a random walk with drift that turns out to match the given density function (the result is the second set of animations).
Thanks, I have an EE education, but I didn't really understood what charges were doing in a BJT. I can use them and apply the formulas, but I never really "grokked" them. This makes it clearer.
This is one of the coolest animation/diagrams I've ever seen, I wish they had them when I did this at uni. It sure beats whiteboards with scribbles and arrows all over it...
it kind of looks unrealistic that there's so little flow, but I guess that makes sense for micro-sized transistors, larger ones that can handle several amps at high voltage should behave differently and would be a rather interesting comparison.
I run a (Canadian) ham radio training site[0] and would love to put them in the lessons. With attribution of course.
Edit: Oh gosh, your whole site is full of wonderful illustrations. My niece might finally get her license with these :)
[0]: https://clares.ca
I wonder how different those are to real simulations! Do they treat electrons as point-like, or it's all computation on the fields?
One minor suggestion - show the voltages in all the animations.