PROPERTIES OF NB INAS/NB HYBRID STEP JUNCTIONS/

Experimental results for novel superconductor/semiconductor hybrid sys tems are presented. The junctions have a step-like geometry, employing two Nb electrodes which are evaporated onto a step that is etched in InAs. Such a geometry allows one to fabricate short weak links (approx imately 200nm) as well as to realize a variety of heterostructure pote ntial profiles along the channel between the superconducting electrode s, since this channel is oriented parallel to the growth direction of the heterostructure. Different semiconductor heterostructures, such as low p-doped InAs, whose native surface inversion layer has the charac ter of a two-dimensional electron gas (2DEG), or npn-InAs heterostruct ures, where the 2DEG of a thin (150nm) p-layer is sandwiched between t wo n-InAs layers, are used. By measuring the current-voltage character istics at 4.2K, supercurrents, subharmonic gap structures, as well as excess currents, are observed.