Direct detection at FIR frequencies with niobium tunnel junctions

Measurements have been made on an array of six niobium/aluminum-aluminum oxide/niobium junctions with an integrated bow-tie antenna at 584 GHz. These measurements include examining the response of current-voltage curves at different incident radiation powers, both with and without an applied magnetic field. The measurements also include the responsivity and the noise of the devices as direct detectors. A planar superconducting quantum interference device (SQUID) was used as the low-frequency amplifier, and a chopped far infrared (FIR) laser generated the radiation. Comparisons with theoretical predictions show good fits to the current-voltage curves, except at the highest powers where there is evidence of heating and possibly nonequilibrium processes. Current responsivities of greater than one-half of the quantum limit and a noise equivalent power of 2*10/sup 1-4/ W/ square root Hz have been obtained.<>