Fabrication and characterization of mesoscopic superconductor–semiconductor hybrid structures

We have deposited superconducting niobium films on high mobility InAs:GaSb quantum wells. The films are patterned with gaps containing up to four niobium lines. The size of the lines and the spacing between them is less than the electron mean free path in the quantum well and ballistic effects are therefore expected to play a role in the current transport. Differential resistance measurements show evidence of supercurrents of up to 10 μA in each of the hybrid structures as well as enhanced conductivity due to Andreev reflection. The supercurrents are suppressed by magnetic fields of order 50 mT. At higher fields, the resistance minimum associated with Andreev reflection evolves into a resistance maximum for fields such that the cyclotron diameter is smaller than the gaps between the niobium. A detailed explanation of the fabrication process is also presented.