Novel hybrid Nb/InAs/Nb step junctions

We present experimental results for novel superconductor/semiconductor heterostructure hybrid systems, which rely on the use of the two-dimensional electron gas at the surface of p-type InAs. The surface channel is made in an InAs step between Nb contacts. Such a geometry allows fabrication of short weak links (≈100 nm) as well as realization of a variety of heterostructure potential profiles along the channel since the latter is oriented perpendicular to the growth direction of the heterostructure. By measuring the current-voltage characteristics at 4.2 K, we observe supercurrent, subharmonic gap structure, as well as above gap structure and excess current. The junction transparency is estimated to exceed 70%.