Superconductor-semiconductor-superconductor junctions using NbN

We report on the fabrication of the superconductor-semiconductor-supercondu ctor (S-Sm-S) junction formed by two superconducting NbN electrodes and a t wo-dimensional electron gas (2DEG) in an Al0.7Ga0.3Sb/InAs heterostructure and we describe the superconducting characteristics we obtained. A critical current I-C of similar to 0.9 mu A at similar to 70 mK was obtained for th e first time in the S-Sm-S junction using NbN. Although T-C of NbN was abou t 12 K, I-C decreased with increasing temperature and then disappeared at s imilar to 1.7 K. This phenomenon can be qualitatively explained by consider ing that the 2DEG underneath the NbN changed places with the pseudo-superco nductor because of proximity-induced superconductivity.