Improved Nb-Si-Nb SNAP devices

We have compared the tunneling characteristics of Nb-Si-Nb junctions whose amorphous silicon barriers have been sputtered in pure Ar with those sputtered Ar-H
2
plasmas as well as in various combinations. We observe lower subgap currents with composite barriers which comprise a central region which is hydrogenated but which is sandwiched between two thin unhydrogenated layers. The improved tunneling characteristics may be associated with the lower density of localized states in the hydrogenated silicon.