  We report on fabrication of single-electron transistors using InAs nanowires
with epitaxial aluminium with fixed tunnel barriers made of aluminium oxide.
The devices exhibit a hard superconducting gap induced by the proximized
aluminium cover shell and they behave as metallic single-electron transistors.
In contrast to the typical few channel contacts in semiconducting devices, our
approach forms opaque multichannel contacts to a semiconducting wire and thus
provides a complementary way to study them. In addition, we confirm that
unwanted extra quantum dots can appear at the surface of the nanowire. Their
presence is prevented in our devices, and also by inserting a protective layer
of GaAs between the InAs and Al, the latter being suitable for standard
measurement methods.
