2, University of Twente, Enschede, , Netherlands
Hybrid devices comprised of topological insulator (TI) nanostructures in proximity to superconductors (SC) are expected to pave the way towards topological quantum computation. Fabrication under ultra-high vacuum conditions is necessary to attain high quality of TI-SC hybrid devices because the physical surfaces of V-VI three-dimensional TIs suffer from degradation at ambient conditions. I will present an in-situ process, which allows to fabricate such hybrids by combining molecular beam epitaxy and stencil lithography. Here, we prepare a Si/SiO2/Si3N4 substrate by means of e-beam lithography and reactive ion etching to process Si3N4 bridges. A dip hydrofluoric acid removes the SiO2 underneath the Si3N4 to obtain freestanding Si3N4 bridges above the Si substrate. These Si3N4 bridges function as a shadow mask during the MBE growth that allow to realize high-quality in-situ grown (Bi,Sb)2Te3/Nb Josephson junctions on the nanometer scale. These in-situ Josephson junctions show nearly perfect interface transparency and very large products. The Shapiro response of radio frequency measurements indicates the presence of gapless Andreev bound states, so-called Majorana bound states.