I would recommend to stay away from AI… everyone and their dog are into the topic right now so you’ll probably face fierce competition in finding a job when the current hype is over.

We’re always looking for good students in anything related to systems if this is your thing - OS, distributed systems, compilers, virtualisation, hardware design/codesign, system level security and all sorts of embedded systems topics. Most of the students here in Germany choose to go to industry after graduating (which pays quite a bit better than universities right now in these areas), so we have quite some trouble to find good PhD students…