Photons heat electrons in superconducting photodetector

Photons heat electrons in superconducting photodetector

Researchers at the University of Rochester (Rochester, NY) and Moscow State Pedagogical University (Moscow, Russia) have developed a superconducting hot-electron photodetector with properties that include a speed of 25 GHp and the capability of detecting single photons. Made of niobium nitride and cooled to just below its superconduction transition temperature of 11.7 K, the detector operates by forming a cascade of electrons when struck by a photon. The cascade is energetic enough that the detector temporarily loses superconductivity, creating an electrical signal. A typical detector has an active area consisting of five parallel stripes, each 6 µm long and 0.6 µm wide.

When excited by light with a wavelength of 0.79 µm, the detector has a voltage responsivity of 40,000 V/W and a current responsivity of 220 A/W--the latter is more than two orders of magnitude higher than that of any semiconductor photodetector. The quantum efficiency of the device reaches 340, showing a large intrinsic gain. The detector is sensitive to wavelengths extending to 10 µm. The researchers envision uses for the detector in telecommunications and infrared astronomy. Contact Roman Sobolewski at [email protected].