Physics – Condensed Matter – Superconductivity
Scientific paper
Jun 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999itas....9.2935s&link_type=abstract
IEEE Transactions on Applied Superconductivity, vol. 9, issue 2, pp. 2935-2939
Physics
Condensed Matter
Superconductivity
Scientific paper
We discuss the design for a submillimeter-wave photometer, using a combination of superconducting and single-electron devices, which would have high quantum efficiency, very low noise-equivalent powers, and eventually even submicrosecond timing resolution. The absorption of above-gap photons occurs in a small strip of superconducting Al, whose normal-state resistance can be matched efficiently to an antenna of a higher gap (Nb) superconductor. The quasiparticles produced by photon absorption are then confined via Andreev reflection, and forced to tunnel through a small SIS tunnel junction. The tunneling time is much shorter than the known (> 10 microsec) quasiparticle recombination time, so collection efficiency will be high. The device sensitivity would be limited by the small subgap current in the high-quality Al/AlOx/Al tunnel junction at temperatures (100 mK) well below Tc. Scaling based on the larger junctions used in X-ray detector applications suggests that the total dark current can be < 0.1 pA, or of order l0^5 electrons/second, corresponding to an NEP of less than l0^-19 W/sqrt(Hz) at 500 microns (600 GHz). The photocurrent will be measured using a fast single-electron transistor (RF-SET), which allows a shot-noise-limited performance even for the very small currents delivered from this low capacitance and high impedance SIS junction. Results of initial fabrication and dc characterization of an integrated photodetector are also given.
Delsing Per
Moseley Samuel Harvey
Schoelkopf Robert J.
Stahle Carl M.
Wahlgren P.
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