Terahertz electromagnetic-wave detector using Nb-based superconducting tunnel junction on LiNbO3 substrate absorber

We have been developing terahertz (THz) wave detectors using superconducting tunnel junctions (STJs). The STJs consist of the Nb/Al/AlOx/Al/Nb structure. We fabricated THz-wave detectors on LiNbO3 substrates that have a high absorption coefficient for the frequency range of 1012 Hz. Two kinds of signals were detected when the THz-wave was irradiated from the substrate side. One was an indirect signal related to the generation of phonons. The other was a signal that corresponds to directly generated quasi-particles in the Nb electrode of the STJ. The pulse height of the indirect signal was larger than that of the latter signal. To enlarge the detector area, we designed a STJ that has different areas of the base electrode and top electrode. In this paper, the characteristics of the THz-wave detector area will be discussed.2007 Elsevier B.V. All rights reserved.