Shadowing of epitaxial superconductors on selectively grown in-plane semiconductor wires for advanced quantum devices

In superconductor-semiconductor systems, a clean interface between superconductor and semiconductor is crucial for quantum transport studies. Advances in epitaxial Al growth on low-dimensional semiconductors have resulted in enhanced features of superconducting proximity effect. In addition, development of clean junctions by in-situ shadowing has led to further improvement of superconducting features in 1D nanowire-based systems. Here we demonstrate a shadowing scheme of epitaxial superconductors on in-plane quantum wires by selective-area growth. Shadow wall structures are pre-fabricated next to wire-shape trenches. After epitaxial growth of semiconductor wires on the trenches, Al deposition is carried out at an angle between 40 and 60 degrees from the normal direction of the substrate. The shadowing of Al results in clean Al-semiconductor junctions based on the shape of the shadow wall structures. This shadow scheme can be applied to any selective-area growth wires by various techniques such as molecular beam epitaxy, chemical beam epitaxy, and metalorganic vaporphase epitaxy. We further discuss transport studies in devices prepared by this scheme as well as deposition of another superconductor with a higher superconducting transition temperature.