A photodetector with high responsivity has been fabricated with a high quality Y1Ba2Cu3O7−δ film on a regular SrTiO3 (100) substrate that has no thinning or etching. The film exhibits a precipitation-free morphology and has an extremely smooth surface having a rms roughness smaller than 5 nm. The film was patterned into a 25×650 μm2 long microbridge by a conventional photolithography technique. The Tco of the microbridge can be tuned by applying different bias currents, which results in a tunable operation temperature of the photodetector at 77.35±1 K. This makes it operationally more practical and economical. The noise voltage at 10 mA bias current is less than the resolution of our setup, 15 nV  Hz−0.5. A high responsivity of 2.3×103 V/W was obtained when a bias current of 8 mA and a low power density He–Ne laser of 0.08 J/cm2 s chopped at 2 Hz were applied on the microbridge at 77.35 K. Under the same condition, the noise equivalent power (NEP) and detectivity (D*) have been measured to be 4.34×10−12 W Hz−0.5 and 3×109 cm Hz0.5 W−1, respectively.

Abstract. Airglow imaging at mid-latitude stations often show intensity modulations associated with medium scale travelling ionospheric disturbances (MSTID), while those carried out near the equatorial regions reveal depletions caused by equatorial plasma bubbles (EPB). Two all sky cameras are used to observe plasma depletions in the 630.0 nm emission over the equatorial ionization anomaly (EIA) region, Taiwan (23 • N, 121 • E; 13.5 • N Magnetic) during 1998-2002 and 2006-2007. The results show EPB and MSTID depletions in different solar activity conditions. Several new features of the EPB depletions such as bifurcation, secondary structure on the walls, westward tilt, etc., are discussed in this paper. Evidence of tilted depletions with secondary structures developing on the eastern wall that later evolve to appear as bifurcations, are presented for the first time. Moreover, detail investigations are carried out using International Reference Ionosphere (IRI) model as well as the electron density from Ionosonde and Global Positioning System (GPS) Occultation Experiment (GOX) onboard FORMOSAT-3/COSMIC satellite, to understand the conditions that favor the propagation of MSTID to the latitude of Taiwan.

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Three Y1Ba2Cu3O7−δ superconducting thin films with 20%, 60%, and 100% coverage of precipitates were fabricated into microbridges of 25×650 μm2 by a conventional photolithography method. These microbridges exhibit a Tco(R=0) from 83.6 to 87.2 K and a transition width of about 1.8 K. These also have (dR/dt)max values of about 71–78 Ω/K. We find that the fewer the precipitates on the film, the better the thermal conduction, and a larger responsivity (S) can be achieved. The best responsivity of 783 V/W measured at Ib=8 mA, Top=86.8 K, and f=2 Hz for various wavelengths of light sources is obtained from the film with 20% precipitation. The photoresponse signals decay exponentially with the precipitation coverages, which indicates that these precipitates behave as thermal resistance layers that smooth out the ac incident signal, suppress the rise in microbridge temperature, and result in a smaller photoresponse signal for the bolometer.

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