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27 Mar 2000

Volume 76, Issue 13, pp. 1641-1784

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Noise and conversion properties of Y–Ba–Cu–O Josephson mixers at operating temperatures above 20 K

Oliver Harnack, Marian Darula, Stephan Beuven, and Hermann Kohlstedt

Appl. Phys. Lett. 76, 1764 (2000); http://dx.doi.org/10.1063/1.126160 (3 pages) | Cited 5 times

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We have measured the noise performance and conversion efficiency of Y–Ba–Cu–O bicrystal Josephson mixers at operating temperatures between 20 and 60 K and at operating frequencies around 90 GHz. A double-sideband mixer noise temperature of about 1600 K and a conversion efficiency of −10 dB at 20 K operating temperature has been measured using the Y-factor method. The absorbed local oscillator power was in the range of 10 nW. The dependence of the mixer performance on the normalized frequency Ω and the fluctuation parameter Γ has been studied. In accordance with the resistively shunted junction model, the experimental data show the presence of excess noise. The temperature dependence of the mixer noise temperature can be explained by the variation of the linewidth of the Josephson oscillations with the operating temperature. © 2000 American Institute of Physics.
Show PACS
85.25.Cp Josephson devices
84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors
84.40.-x Radiowave and microwave (including millimeter wave) technology
85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors

Al composition dependence of breakdown voltage in AlxGa1−xN Schottky rectifiers

A. P. Zhang, G. Dang, F. Ren, J. Han, A. Y. Polyakov, N. B. Smirnov, A. V. Govorkov, J. M. Redwing, X. A. Cao, and S. J. Pearton

Appl. Phys. Lett. 76, 1767 (2000); http://dx.doi.org/10.1063/1.126161 (3 pages) | Cited 27 times

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Planar geometry, lateral Schottky rectifiers were fabricated on high resistivity AlxGa1−xN (x = 0–0.25) epitaxial layers grown on sapphire substrates. The reverse breakdown voltages of unpassivated devices increased with Al composition, varying from 2.3 kV for GaN to 4.3 kV for Al0.25Ga0.75N. The reverse current–voltage (I–V) characteristics showed classical Shockley–Read–Hall recombination as the dominant mechanism, with I∝V0.5. The reverse current density in all diodes was in the range 5–10×10−6 A cm−2 at 2 kV. The use of p+ guard rings was effective in preventing premature edge breakdown and with optimum ring width increased VB from 2.3 to 3.1 kV in GaN diodes. © 2000 American Institute of Physics.
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85.30.Kk Junction diodes
84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables
73.61.Ey III-V semiconductors
73.50.Fq High-field and nonlinear effects

Transient electroluminescence under double voltage pulse: Charge accumulation in light-emitting devices based on alizarin violet

Sharmistha Das and Amlan J. Pal

Appl. Phys. Lett. 76, 1770 (2000); http://dx.doi.org/10.1063/1.126162 (3 pages) | Cited 18 times

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Transient characteristics of organic light-emitting devices with alizarin violet as emitting material have been studied. A sequence of two voltage pulses separated by a time delay was applied. From the transient response of electroluminescence, the effects of accumulated and injected carriers have been separated out. During the first voltage pulse, the intrinsically accumulated charges generated a peak in luminance, which was absent during the latter pulses. The separation time between the two pulses has been varied to study the relaxation dynamics of the accumulated carriers. By varying the molar concentration of the emitting material, we have studied the parameters related to electron barrier modification and discussed the contribution of accumulated carriers in device operation. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
73.61.Ph Polymers; organic compounds
78.66.Qn Polymers; organic compounds
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