What, you don't think you could whip up a GaAs foundry in the post Apocalypse?
(Actually, between the birdman and Rev, they might actually find a way to pull it off.)
Funny you should mention that...
We'd Start with silicon..or germanium. The latter is easier, and since we'd be the only folks who can make chips...yeah...there would definitely be a few "it's good to be da king" moments
Er. Actually, in the plot, the facility's cover is Pennsylvania Alternative Energy (Post Apocalyptic Enterprises being the real name) that makes solar panels and other alternative energy junk. Which obviously gives a really good excuse to have silicon manufacturing stuff lying around.
To give away the plot. We discover space rock on collision path. Contractors are paid to make a coherent beam combining space fiber laser to vaporize spots on the space rock surface to provide delta V to make the space rock miss earth. Essentially, the laser I suspect you've worked on for you know who, but in space. NASA/Administration screws it up by attempting big kaboom for PR rather than couple hundred taps that are about as interesting as watching paint dry. So the earth is saved from ELE, just screwed in the process when a couple thousand large space rocks hit about everywhere.
While simultaneously planning on throwing them under the bus, government is paying them to build barely underground bunkers ostensibly for some percentage of the population, but in reality primarily as their own hidey hole. Politicians are too thick to realize that defense contractors aren't stupid and the mil brass know enough to look the other way. So they have to be on the down low, or the administration will throws them to the wolves, likely to be literally ripped limb from limb if the media blames them as being evil profiteers that killed the world. So, they're trying to covertly build their own ark while hiding from both the general population as well as the government.
A solar panel place would be awfully handy starting ground for oh, chip manufacturing and ghetto FLIR units that you just described, if one was being sneaky. At least, for trying to hide large supply purchases of silicon and related material. And get tax credits for while doing so.
That's why it's admittedly taking so long, I want literally every scrap of science to be right and well planned out.
Admit it, reading the above, you thought it'd be an eerily possible scenario.