CONTACT RESISTANCE OF SUPERCONDUCTOR-SEMICONDUCTOR INTERFACES - THE CASE OF NB-INAS/ALSB QUANTUM-WELL STRUCTURES

The contact resistances of widely spaced (much greater than 1 mum) superconducting Nb contacts to InAs-AlSb quantum wells indicate a resistive behavior of the interface, with a positive electron transfer length, while narrow-spaced contacts (less-than-or-equal-to 1 mum) exhibit a strong conductance enhancement at low bias with pronounced subgap features. The data are interpreted in terms of a model in which the current across the interface is carried by Andreev reflections. From the measured transfer lengths, we estimate a single-event Andreev reflection probability of about 3.5%, but with a high backplane-enhanced overall reflection probability.