NbN/BN granular films—a sensitive, high-speed detector for pulsed far-infrared radiation

Thin superconducting, granular films of NbN/BN are investigated as photodetectors for pulsed, far-infrared radiation. These films may be thought of as a random network of Josephson junctions. The absorption of photons causes the film resistance to increase. This is thought to occur by destroying the phase coherence of the Cooper pair wave function among the junctions. This resistance change can be used as a basis for a photodetector. It is found that the NbN/BN thin-film detectors have response times faster than 1 ns, and sensitivities of about 0.7 V/W when terminated to 50 Ω, at wavelengths of about 0.50 mm.