Ultimate quantum efficiency of a superconducting hot-electron photodetector

The quantum efficiency and current and voltage responsivities of fast hot-e lectron photodetectors, fabricated from superconducting NbN thin films and biased in the resistive state, have been shown to reach values of 340, 220 A/W, and 4 x 10(4) V/W, respectively, for infrared radiation with a wavelen gth of 0.79 mu m. The characteristics of the photodetectors are presented w ithin the general model, based on relaxation processes in the nonequilibriu m electron heating of a superconducting thin film. The observed, very high efficiency and sensitivity of the superconductor absorbing the photon are e xplained by the high multiplication rate of quasiparticles during the avala nche breaking of Cooper pairs. (C) 1998 American Institute of Physics. [S00 03-6951(98)03252-5].