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 J(C)=0.2-70 kA/cm(2). The counter and base NbN electrodes of the tunnel junctions had the same T-C and 20 K resistivity at about 15.7 K and 60 mu Omega -cm, respectively. X-ray analysis showed that all the layers that formed the tunnel junctions grew epitaxially. In the range of J(C)=0.2-15 kA/cm(2), 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 (V-m=40-96 mV). (C) 2001 American Institute of Physics.