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

摘要

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 I_CR_N 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.