Parameters of the Tunnel Barrier of Superconducting Niobium-Based Structures

The main parameters of the tunnel barrier of Josephson Nb/AlO_x/Nb and Nb/AlN/Nb junctions are estimated in a wide range of the current density using the Simmons method. The dependences of the tunnel barrier height and width of the resistivity are determined experimentally for each type of the junctions. A decrease in the tunnel barrier height of the junction with the AlN interlayer by 0.3 eV as compared to an oxide junction enables us to obtain the junctions with a current density higher than 15 kA/cm² at an insulating layer thickness of 10 Å allowable technologically, which gives the possibility to obtain quality parameter R_j/R_n no lower than 25.