  Superconducting circuits are exceptionally flexible, enabling many different
devices from sensors to quantum computers. Separately, epitaxial semiconductor
devices such as spin qubits in silicon offer more limited device variation but
extraordinary quantum properties for a solid-state system. It might be possible
to merge the two approaches, making single-crystal superconducting devices out
of a semiconductor by utilizing the latest atomistic fabrication techniques.
Here we propose superconducting devices made from precision hole-doped regions
within a silicon (or germanium) single crystal. We analyze the properties of
this superconducting semiconductor and show that practical superconducting
wires, Josephson tunnel junctions or weak links, superconducting quantum
interference devices (SQUIDs), and qubits are feasible. This work motivates the
pursuit of "bottom-up" superconductivity for improved or fundamentally
different technology and physics.
