摘要:

We report upon the fabrication and characterization of the firstn‐type resonant tunneling diodes in the SiGe materials system. The devices fabricated were Si/SiGe/Si/SiGe/Si double‐barrier diodes, employing strain‐relieved SiGe as the barrier layers surrounding pseudomorphic tensile strained Si. These devices were prepared using ultrahigh vacuum chemical vapor deposition. Negative differential conductance is observed at room temperature in these devices with a peak‐to‐valley ratio of 1.2. The corresponding value at 77 K is 1.5.

ISSN:0003-6951    

DOI:10.1063/1.106319

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We have investigated the structural properties of Bragg reflectors grown by molecular beam epitaxy. The reflectors consist of quarter‐wavelength stacks of AlAs/ AlxGa1−xAs. We find a strong dependence of the interface quality on the substrate growth temperature, the Al composition in the ternary alloy, and the presence of impurities in AlAs. We have classified the interface disorder into two categories: interface roughness and structural waviness. We ascribe interface roughness to the segregation of oxygen during AlAs growth. The structural waviness originates from differing surface migration kinetics of Al and Ga which results in phase separation during growth of AlGaAs.

ISSN:0003-6951    

DOI:10.1063/1.106421

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We explored the reactivity of gold on cleaved 2212 BiCaSrCuO by synchrotron‐radiation photoemission spectroscopy. We found no evidence for reactivity when the substrate was at room temperature, similar to what has been reported for very low temperatures (20 K). At intermediate temperatures (100 K), however, clear evidence was found of a chemical reaction with formation of a localized nonmetallic phase. These findings have potentially important implications for the manufacturing of devices based on BiCaSrCuO.

ISSN:0003-6951    

DOI:10.1063/1.106320

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

High quality YBa2Cu3O7−x/normal‐metal/YBa2Cu3O7−xedge‐geometry weak links have been fabricated using nonsuperconducting Y‐Ba‐Cu‐O barrier layers deposited by laser ablation at reduced growth temperatures. Devices incorporating 25–100 A˚ thick barrier layers exhibit current‐voltage characteristics consistent with the resistively shunted junction model, with strong microwave and magnetic field response at temperatures up to 85 K. The critical currents vary exponentially with barrier thickness, and the resistances scale linearly with Y‐Ba‐Cu‐O interlayer thickness and device area, indicating good barrier uniformity, with an effective normal metal coherence length of 20 A˚.

ISSN:0003-6951    

DOI:10.1063/1.106321

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Bulk superconductivity was observed in the new system (InxPb0.75−xCu0.25)Sr2(Ca0.5Y0.5)Cu2O7−&dgr;. An increase in indium doping, 0≤x≤0.2, into the Pb sites results in an increase in the superconducting transition temperatureTcfrom 45 K forx=0 to 60 K forx=0.2. For nominal compositionsx≳0.2, a decrease inTcwas observed, and an increase in the concentration of an impurity phase. From the results of the x‐ray diffraction and energy‐ dispersive spectrometry, we identify the phase responsible for the superconductivity to be [In0.06(1)Pb0.69(1)Cu0.25]Sr1.99(7)[Ca0.47(1)Y0.53(2)]Cu2O7−&dgr;; this phase resulted from the synthesis of a sample of nominal composition (In0.2Pb0.55Cu0.25)Sr2(Ca0.5Y0.5)Cu2O7−&dgr;.

ISSN:0003-6951    

DOI:10.1063/1.106322

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Our YBa2Cu3O7−xthin‐film magnetometer consists of a dc superconducting quantum interference device with bi‐epitaxial Josephson junctions, fabricated on one chip, and a flux transformer with a multiturn input coil, fabricated on a second chip. Photolithographic processing is used to pattern all layers. The magnetometer operates in a flux‐locked loop at temperatures up to 81 K, with the flux transformer improving the magnetic field sensitivity by a factor of 83±3. The low‐frequency rms magnetic field noise scales approximately as 1/f1/2, wherefis the frequency, with a magnitude of 0.6 pT Hz−1/2at 10 Hz and 0.09 pT Hz−1/2at 1 kHz with the magnetometer immersed in liquid N2.

ISSN:0003-6951    

DOI:10.1063/1.106323

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Millimeter mixers have been fabricated from epitaxial films of Tl2CaBa2Cu2O8, using a bowtie antenna structure integrated with grain‐boundary weak links that were deliberately formed during film growth. The bowtie antenna was utilized for broadband millimeter wave coupling of the radiation into the weak links. Heterodyne mixing of signals at bothVband (55 GHz) andWband (94 GHz) frequencies, and subharmonic mixing atVhas been observed at liquid nitrogen temperature for zero and finite bias voltage conditions. The dependence of the IF output on temperature, bias voltage, and millimeter wave signal power has been studied. Efficient mixing with bias voltage exhibited strong signals right up toTc(101 K).

ISSN:0003-6951    

DOI:10.1063/1.106324

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Scanning electron acoustic microscopy (SEAM) has been used in the observation of domain walls in iron‐ and cobalt‐based amorphous alloys ribbons. Controlled magnetic annealing experiments enabled the direct identification of domain walls in SEAM micrographs. Walls in perpendicular anisotropy regions of the high magnetostriction samples show a particular high contrast, probably related to the wall stress field.

ISSN:0003-6951    

DOI:10.1063/1.106325

出版商:AIP    

年代:1991

数据来源: AIP