SUPERCONDUCTING FAST DETECTOR BASED ON THE NONEQUILIBRIUM INDUCTANCE RESPONSE OF A FILM OF NIOBIUM NITRIDE

A new type of fast detector is proposed, whose operation is based on t he variation of the kinetic inductance of a superconducting film cause d by nonequilibrium quasiparticles created by the electromagnetic radi ation. The speed of the detector is determined by the rate of multipli cation of photo-excited quasiparticles, and is nearly independent of t he temperature, being less than 1 ps for NbN. Models based on the Owen -Scalapino scheme give a good description of the experimentally determ ined dependence of the power-voltage sensitivity of the detector on th e modulation frequency. The lifetime of the quasiparticles is determin ed, and it is shown that the reabsorption of nonequilibrium phonons by the condensate has a substantial effect even in ultrathin NbN films 5 nm thick, and results in the maximum possible quantum yield. A low co ncentration of equilibrium quasiparticles and a high quantum yield res ult in a detectivity D = 10(12) W-1 . cm . Hz(1/2) at a temperature T = 4.2 K and D = 10(16) W-1 cm Hz(1/2) at T= 1.6 K. (C) 1997 American Institute of Physics. [S1063-7850(97)02906-6].