Abstract-Terahertz direct-detection behavior of niobium nitride superconducting tunnel junctions above liquid helium temperature

Zheng Wang1,2, Dong Liu1,2, Shao-liang Li1,2, Jing Li1,2 and Sheng-Cai Shi1,2

zhwang@pmo.ac.cn http://iopscience.iop.org/0953-2048/27/7/075003scshi@pmo.ac.cn

1 Millimeter & Submillimeter Wave Lab, Purple Mountain Observatory, CAS, Nanjing, Jiangsu, 210008, People's Republic of China
2 Key Laboratory of Radio Astronomy, CAS, Nanjing, Jiangsu, 210008, People's Republic of China 

Niobium nitride (NbN) superconducting tunnel junctions (STJs) have an energy gap nearly double that of niobium STJs, making them potential sensitive detectors that operate at higher frequencies and temperatures. In this paper, we investigate the direct-detection behavior (i.e. the spectral response, current responsivity, noise characteristics, and noise equivalent power (NEP)) of a 500 GHz NbN STJ detector at temperatures from approximately 5 to 9 K. The detector shows an uncorrected NEP of 3.8 × 10−13W/around 5 K and 1.5 × 10−12 W/at 9 K. Its performance can be further improved by adopting a cryogenically cooled readout circuit and fabricating the device with a wiring layer of higher critical-transition temperatures.