OVERDAMPED NBN JUNCTIONS WITH NBNX BARRIERS FORMED BY PLASMA NITRIDATION

We have fabricated NbN Josephson junctions with NbN, barriers formed b y plasma nitridation on the surface of the base superconductive NbN la yer. Both nonhysteretic junctions (overdamped junctions) and small-hys teretic ones have been obtained at 4.2 K by changing plasma nitridatio n conditions. An overdamped junction showed a product of the critical current I-c and junction resistance R-n (an IcRn product) of 0.95 mV a t 4.2 K and the I-c exponentially decreased with increasing temperatur e. On the other hand, a small-hysteretic junction showed Superconducto r-Insulator-Superconductor (SIS)like characteristics in the temperatur e dependence of I-c and its current-voltage characteristics changed to nonhysteretic ones at the temperature more than 8 K. The IcRn product for the junction was 0.91 mV at 8.2 K. (C) 1998 Elsevier Science Ltd. All rights reserved.