Comparison of the THz Direct-Detection Behaviors of Nb and NbN Superconducting Tunnel Junctions

Superconducting SIS (superconductor-insulator-superconductor) tunnel junctions are promising application prospect in the incoherent detection of astronomy observation. In this paper, the direct detection performances of Nb and NbN based superconducting SIS junctions, which cover about 250 GHz and 140 GHz centered at 600 GHz respectively, are characterized at a bath temperature of 4.2 K. The experiments show that Nb and NbN based SIS junctions have a current shot noise of 2.5 times 10^-12 and 3.1 times 10^-12 A/radicHz, a current responsivity of 303 and 187 A/W (corresponding to the quantum efficiency of 0.67 and 0.43) respectively. Thus their respective NEPs are 8.4 times 10^-15 and 1.7 times 10^-14W/radic Hz.