Superconducting junctions using AlGaAs/GaAs heterostructures with high H-c2 NbN electrodes

We investigated a superconductor-semiconductor-superconductor junction formed by two superconducting NbN electrodes and a two-dimensional electron gas (2DEG) in an AlGaAs/GaAs heterostructure. We obtained a good ohmic contact between NbN/AuGeNi electrodes and 2DEG by annealing them at 450degreesC for 1 min in an N-2 atmosphere. We observed a decrease in the resistance caused by Andreev reflection (AR) within the superconducting energy gap voltage in a zero magnetic field in this structure. We found that the peculiar features of the magnetoresistance in the transition region can be qualitatively explained by considering the existence of the AR in high magnetic fields. (C) 2002 Elsevier Science B.V. All rights reserved.