Fabrication and characterization of epitaxial NbN/MgO/NbN Josephson tunnel junctions

We fabricated epitaxial NbN/MgO/NbN Josephson tunnel junctions with good tunneling characteristics in the range of JC=0.2–70 kA/cm2. The counter and base NbN electrodes of the tunnel junctions had the same TC and 20 K resistivity at about 15.7 K and 60 μΩ-cm, respectively. X-ray analysis showed that all the layers that formed the tunnel junctions grew epitaxially. In the range of JC=0.2–15 kA/cm2, the tunnel junctions fabricated had large gap voltages (5.6–5.9 mV), narrow gap widths (less than 0.1 mV), high ICRN products (2.6–3.8 mV), and small subgap leakage current (Vm=40–96 mV).

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