Characterization of NbN/AlN/NbN tunnel junctions

We report on tunneling properties and interface structures for high-quality NbN/AlN/NbN tunnel junctions fabricated on ambient temperature MgO substra tes, Junction quality and electrical parameters were systematically investi gated in a very wide range for current density. The junctions show a very g ood junction quality with a high gap voltage, large I,RN product, and large R-sg/R-N ratio as the current density varied from 100 A/cm(2) to above 100 kA/cm(2). The average barrier heights of the NbN/AlN/NbN tunnel junctions are calculated from the barrier thickness dependence of the critical curren t density. We found that the current density has two distinct types of depe ndency on the AIN barrier thickness, corresponding to two average barrier h eights in different regions for the current density.