I know Steven Johnson (whose group develops MEEP) well, since he is a Julia core developer, so if you had questions about MEEP in particular, I can probably get those answered also. He mostly does nanophotonics though, so it might be more suited to that application. My understanding is that for TCAD applications you want to make some symbolic simplifications to speed up the simulation. Haven't really dug too deep into this myself yet though, but as I said, @User, if there are specific things you need to get answers to, I can probably find them.