InAs nanowire with epitaxial aluminium as a single-electron transistor   with fixed tunnel barriers
  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. 
M. Taupin, E. Mannila, P. Krogstrup, V. F. Maisi, H. Nguyen, S. M.   Albrecht, J. Nygard, C. M. Marcus, and J. P. Pekola
cond-mat.mes-hall cond-mat.supr-con