Tunnel junctions with Nb3Ge base electrode

For quasiparticle mixers for very high frequencies and ultrafast samplers, tunnel junctions with a large energy gap are needed. Large gap voltages should be possible with high-Tcmaterials like Nb3Sn or Nb3Ge. We describe an in-situ preparation process for these junctions using Nb3Ge as base electrode, and different superconductors as top electrode material. Because of poor results with native oxide layers, an artificial barrier was used. For this purpose, several oxides have been investigated. First results on these contacts, using several oxides and fluorides as barriers and Pb and NbN as top electrodes are presented.