Abstract
To enable the design of fully epitaxial NbN–SIS mixers, we estimated the penetration depth of epitaxial NbN thin films in the submillimeter wave region. Tunnel junctions with sizes of 40 × 3, 20 × 3, and 10 × 3 μm 2 were fabricated to observe Fiske steps. X-ray analysis showed that all the NbN and MgO layers that formed the tunnel junction were epitaxially grown. Based on the harmonic Fiske steps, the penetration depth of the epitaxial NbN films was estimated in the frequency range from 0.1 to 1.1 THz. Using the Mattis–Bardeen theory, we found that the measured penetration depths in the submillimeter wave region were larger than the calculated results. This result indicates that it is important to design fully epitaxial NbN–SIS mixers based on the measurement results of penetration depth.
Published Version
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