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Danerud, M., Winkler, D., Lindgren, M., Zorin, M., Trifonov, V., Karasik, B. S., et al. (1994). Nonequilibrium and bolometric photoresponse in patterned YBa2Cu3O7−δ thin films. J. Appl. Phys., 76(3), 1902–1909.
Abstract: Epitaxial laser deposited YBa2Cu3O7−δ films of ∼50 nm thickness were patterned into detectors consisting of ten parallel 1 μm wide strips in order to study nonequilibrium and bolometric effects. Typically, the patterned samples had critical temperatures around 86 K, transition widths around 2 K and critical current densities above 1×106A/cm2 at 77 K. Pulsed laser measurements at 0.8 μm wavelength (17 ps full width at half maximum) showed a ∼30 ps response, attributed to electron heating, followed by a slower bolometric decay. Amplitude modulation in the band fmod=100 kHz–10 GHz of a laser with wavelength λ=0.8 μm showed two different thermal relaxations in the photoresponse. Phonon escape from the film (∼3 ns) is the limiting process, followed by heat diffusion in the substrate. Similar relaxations were also seen for λ=10.6 μm. The photoresponse measurements were made with the film in the resistive state and extended into the normal state. These states were created by supercritical bias currents. Measurements between 75 and 95 K (i.e., from below to above Tc) showed that the photoresponse was proportional to dR/dT for fmod=1 MHz and 4 GHz. The fast response is limited by the electron‐phonon scattering time, estimated to 1.8 ps from experimental data. The responsivity both at 0.8 and 10.6 μm wavelength was ∼1.2 V/W at fmod=1 GHz and the noise equivalent power was calculated to 1.5×10−9 WHz−1/2 for the fast response.
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Nebosis, R. S., Steinke, R., Lang, P. T., Schatz, W., Heusinger, M. A., Renk, K. F., et al. (1992). Picosecond YBa2Cu3O7−δdetector for far‐infrared radiation. J. Appl. Phys., 72(11), 5496–5499.
Abstract: We report on a picosecond YBa2Cu3O7−δ detector for far‐infrared radiation. The detector, consisting of a current carrying structure cooled to liquid‐nitrogen temperature, was studied by use of ultrashort laser pulses from an optically pumped far‐infrared laser in the frequency range from 25 to 215 cm−1. We found that the sensitivity (1 mV/W) was almost constant in this frequency range. We estimated a noise equivalent power of less than 5×10−7 W Hz−1/2. Taking into account the results of a mixing experiment (in the frequency range from 4 to 30 cm−1) we suggest that the response time of the detector was few picoseconds.
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Uchiki, H., Kobayashi, T., & Sakaki, H. (1987). Photoluminescence and energyâ€loss rates in GaAs quantum wells under highâ€density excitation. J. Appl. Phys., 62(3), 1010–1016.
Abstract: The timeâ€resolved luminescence spectra from excited conduction subbands in three samples of multiâ€quantumâ€well GaAs/AlxGa1-xAs (x=0.3 and 1) semiconductors with several well widths and barrier heights were obtained under highâ€density excitations by a 30â€ps pulsed laser at 532 nm, which generated electron–hole pairs to the concentration of 1010–1013/cm2 per well per pulse at 77 K. The temperature and the Fermi energy of electron were determined by fitting best the constructed timeâ€resolved spectrum to the observed, and the timeâ€dependent electron energy was obtained by using these parameters. The energyâ€loss rates of hot electrons are at least twice smaller than the calculated ones induced by the electronâ€polar phonon scattering, including the screening effect due to the high carrier density.
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