Picosecond hot-electron energy relaxation in NbN superconducting photodetectors
Journal article, 2000

We report time-resolved characterization of superconducting NbN hot-electron photodetectors using an electro-optic sampling method. Our samples were patterned into micron-size microbridges from 3.5-nm-thick NbN films deposited on sapphire substrates. The devices were illuminated with 100 fs optical pulses, and the photoresponse was measured in the ambient temperature range between 2.15 and 10.6 K (superconducting temperature transition TC). The experimental data agreed very well with the nonequilibrium hot-electron, two-temperature model. The quasiparticle thermalization time was ambient temperature independent and was measured to be 6.5 ps. The inelastic electron–phonon scattering time τe–ph tended to decrease with the temperature increase, although its change remained within the experimental error, while the phonon escape time τes decreased almost by a factor of two when the sample was put in direct contact with superfluid helium. Specifically, τe–ph and τes, fitted by the two-temperature model, were equal to 11.6 and 21 ps at 2.15 K, and 10(±2) and 38 ps at 10.5 K, respectively. The obtained value of τe–ph shows that the maximum intermediate frequency bandwidth of NbN hot-electron phonon-cooled mixers operating at TC can reach 16(+4/−3) GHz if one eliminates the bolometric phonon-heating effect.

superconducting microbridges


superconducting mixers

superconducting transition temperature


niobium compounds

electro-optical effects

hot carriers

type II superconductors

electron-phonon interactions


K.S. Il'in

Martin Lindgren

M Currie

A.D. Semenov

G.N. Gol'tsman

Roman Sobolewski

Serguei Cherednichenko

Department of Microelectronics and Nanoscience, Physical Electronics and Photonics

E.M. Gershenzon

Applied Physics Letters

0003-6951 (ISSN) 1077-3118 (eISSN)

Vol. 76 19 2752-2754

Areas of Advance

Nanoscience and Nanotechnology (2010-2017)


Basic sciences

Subject Categories

Other Electrical Engineering, Electronic Engineering, Information Engineering

Condensed Matter Physics



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