Berlin 2008 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 15: Superconductivity: Poster Session
TT 15.51: Poster
Dienstag, 26. Februar 2008, 14:00–18:00, Poster B
Response of NbN ultra-thin superconducting films to optical irradiation — •Dagmar Rall1,3, Konstantin Ilin2, Stefan Wünsch2, Felix Glöckler1, Uli Lemmer1, and Michael Siegel2 — 1Light Technology Institute, University of Karlsruhe, Germany — 2Institute for Micro- and Nanoelectronic Systems, University of Karlsruhe, Germany — 3Karlsruhe School of Optics and Photonics, Germany
We study energy relaxation processes in ultra-thin NbN films suitable for development of hot-electron bolometers and superconducting single photon detectors. Improvements of device performance require optimization of material properties of NbN films focussing on increasing of sensitivity and speed of the detector. The NbN thin films with different thickness and stoichiometry are fabricated by dc reactive magnetron sputtering and patterned into narrow strip lines and terminated by the detecting element. Energy relaxation processes in the films are studied using a time domain technique. NbN strips are cooled below critical temperature in a continuous-flow helium cryostat fitted with high-frequency readout electronics and optical window. Femtosecond laser pulse irradiation absorbed in ultra-thin NbN film excites hot-electrons resulting in a voltage pulse. Time propagation of the response pulse is determined by electron energy relaxation processes via inelastic electron-electron and electron-phonon interaction and escape of non-equilibrium phonons from film to substrate. Results on fs-laser pulse response of NbN thin films with different material properties and geometry of the sample will be presented and discussed.