NbN/BN granular films--A novel broadband bolometric detector for pulsed far infrared radiation

Thin films of NbN/BN are investigated as photodetectors for pulsed, far infrared radiation. It is found that there are two distinct modes of operation for these devices, depending on whether the device is biased in the superconducting or resistive regime. When the device is biased into the resistive region, the absorption of photons decreases its resistance. Conversely, when the device is superconducting, the absorption of photons causes the resistance to increase. The more sensitive mode occurs when the device is biased superconducting. Detector parameters are studied in this condition and are compared to other, more conventional detectors (ie. pyroelectric, point contact diodes, semiconductor photoconductors). It is found that the NbN/BN thin film detectors have response times faster than 1 ns, and sensitivities of about 0.2 V/W.