Fabrication of hybrid superconductor–semiconductor nanostructures by integrated ultraviolet-atomic force microscope lithography

Hybrid superconductor–semiconductor (S–Sm) nanostructures were fabricated by integrating standard ultraviolet photolithography and direct patterning of photoresist with an atomic force microscope (AFM). This novel technology was used to fabricate Nb–InAs–Nb weak links comparable in length to the coherence length. These structures exhibit high critical currents up to 10 μA/μm in planar geometry at 0.3 K. The fabrication protocol is based on the modification of photolithographically defined patterns by AFM static ploughing of the photoresist. Wet chemical etching is subsequently used for the definition of nanoscale S–Sm–S bridges. Additionally Lift-off procedures allowed the fabrication of submicron superconducting bridges. Successful fabrication of the nanostructures was verified by electrical characterization and by AFM and scanning electron microscope structural characterization.