  We report a method for making epitaxial superconducting contacts to
semiconducting nanowires. The temperature and gate characteristics demonstrate
barrier-free electrical contact, and the properties in the superconducting
state are investigated at low temperature. Half-covering aluminum contacts are
realized without the need of lithography and we demonstrate how to controllably
insert high-band gap layers in the interface region. These developments are
relevant to hybrid superconductor-nanowire devices that support Majorana zero
energy states.
