High-quality epitaxial NbN/AlN/NbN tunnel junctions with a wide range of current density

We have developed high-quality epitaxial NbN/AlN/NbN Josephson tunnel junctions with a wide range of current density J(c). The junctions show excellent tunneling properties with a large gap voltage of 5.6 mV and a large IcRN product of 3.5 mV. The quality factor R-sg/R-N is about 60 for the junctions with a J(c) of 2.2 A/cm(2), and above 10 for the junctions with a J(c) of 25 kA/cm(2). The crystal structures across the junction barrier are investigated using x-ray diffraction and cross-sectional scanning transmission electron microscopy, and demonstrate epitaxial growth of the NbN/AlN/NbN trilayers for the wide range of J(c). (C) 2013 AIP Publishing LLC