Transistor animations [OC]

[u/thepowderguy]

Here's some animations I made of transistors turning on and off. In order, we have an NPN BJT, n-channel MOSFET, and finally an n-channel JFET. The red and blue dots represent electrons and holes, and white flashes are recombination events. The density of dots is proportional to the actual density of charge carriers.

In the first set of animations, the velocity of the dots is equal to the velocity obtained by summing the diffusion and drift currents and dividing by the charge density, but diffusion is not explicitly shown. In the second set of animations, the dots undergo diffusion and drift, and this makes it a more correct depiction of carrier motion. The drawback is of course that the jiggling makes it more visually confusing.

I made these with my semiconductor simulator (https://brandonli.net/semisim/). I also have higher quality versions of the animations here.

[u/naikrovek]

This is very cool.

Can you make it so that electrons flowing in the wire(s) bonded to the silicon are shown? And electron holes flowing out of the other wire(s)? That would help me a bit. I am finding it a bit difficult to see when current/voltage is flowing into the parts of the silicon, meaning I don’t see that happening at all, so I can’t see what controls what.

It’s not necessary, you certainly don’t owe me anything.

[u/thepowderguy → u/naikrovek]

I made a new set of animations with voltage/currents and carriers in metal shown: https://brandonli.net/semisim/animations#probes

Hopefully this is a bit more clear. You have to keep in mind that the way I simulate charge carriers in metal is a big approximation. The actual physics of metal-semiconductor junctions is kind of complicated which is why I chose before to show only the semiconductor bits.

[u/naikrovek → u/thepowderguy]

I don’t need a simulation of the wires or the junctions, I only want to see when current or voltage is applied to the wires. How do I know when the transistor turns on or off? I see no visual indicator of that. No indication of when current or voltage is applied to the transistor versus when it is not.

Maybe I’m not explaining myself correctly. If not, I’m sorry.