Josephson tunnel junctions with chemically vapor deposited polycrystalline germanium barriers

Abstract
High quality Josephson tunnel junctions have been fabricated whose tunneling barrier is polycrystalline germanium chemically vapor deposited on a NbN base electrode and covered by a Nb counterelectrode. These junctions have excellent characteristics for device applications: values of Vm (the product of the critical current and the subgap resistance measured at 2 mV and 4.2 K) ranging between 35–48 mV, ideal threshold curves, a steep current rise at the gap voltage, and Josephson current densities from 100 to 1100 A/cm2.