Resonant tunneling in amorphous-silicon-barrier Josephson junctions

We have fabricated amorphous‐silicon‐barrier Josephson junctions to test the theory of resonant tunneling due to localized electron states. The position of a very thin oxide layer embedded in the silicon barrier was varied, with the barrier thickness fixed, in order to observe its effect on resonant tunneling. An expression for the conductance of this structure was derived from the resonant‐tunneling equation and found to agree with our results. We calculate the density of localized states from these measurements and find it is in the range typically obtained from electron‐spin‐resonance measurements. It is also found, as indicated by theory, that the localized states support supercurrent in the same proportion to quasiparticle current as does direct tunneling.