摘要:

High resolution x‐ray diffraction has been used to investigate the structural properties of InxGa1−xAs epitaxial layers grown under tension on InP(100) substrates. The nominal indium composition (x=0.42) corresponds to a small lattice mismatch and a two dimensional growth mode. We have also included for comparison two samples grown under compression covering the mostly strained and the mostly relaxed regimes. Our results show that the residual strain and the asymmetry in strain relaxation along ⟨011⟩ directions are always larger for layers under tension. This can be explained by the difference in dislocation glide velocity induced by a different indium content, by the dissociation of perfect dislocations and partially by the difference in thermal expansion coefficients between substrate and epilayer. The larger asymmetry in strain relaxation for tensile strain layers is interpreted by the existence of microcracks aligned in the [011] direction. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117805

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The remote hydrogen plasma passivation of semi‐insulating InP substrates has been investigated byinsituspectroscopic ellipsometry (SE), to characterize the changes of InP morphology, andexsituphotoluminescence (PL) to reveal the passivation effect of nonradiative centers operated by H atoms. The concurrence of the InP native oxide removal without surface damage (phosphorus ablation) and the passivation by H‐atoms results in a remarkable enhancement of the PL intensity. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117806

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Antenna‐coupled high‐Tcbolometers fabricated from YBa2Cu3O7−&dgr;thin films have been prepared using molecular organic dyes. Light‐harvesting layers derived from these visible and near‐infrared absorbers have been utilized to produce detectors which exhibit wavelength‐selective response characteristics in the visible and near‐infrared spectral regions. Using such hybrid structures, initial studies documenting efficient energy transfer between molecular dye layers and superconductor surfaces have been completed. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117807

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We report on efficient coupling of THz radiation to a high‐Tcsuperconducting hot electron bolometer that is suitable for heterodyne detection. Our quasi‐optical system consisted of a planar self‐complementary spiral antenna on a dielectric substrate clamped to an extended hyperhemispherical lens. The antenna was integrated into a co‐planar line for broadband intermediate frequency matching. Measurements in the homodyne regime at a frequency of 2.5 THz showed a radiation pattern with a beam width of 1° and a coupling efficiency of ≊0.1. We measured, at an intermediate frequency of 1.5 GHz, an output noise temperature of ≊160 K and estimated for the device, operated in the heterodyne regime, a system noise temperature of ≊3×105K. We also discuss possibilities of significant improvement of the sensitivity. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117808

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The bit‐error rate of the Josephson junction single‐flux‐quantum comparator was measured as a function of bias current offset, at clock rates up to 10 GHz. The bit‐error rate versus offset is a smooth curve, measured over 16 decades of incidence, which linearly extrapolates to 10−49for optimal bias. The lowest rate actually measured was 5×10−17, corresponding to 4 errors counted in 130 h. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117809

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Current transport across each of the two YBa2Cu3O7–Au interfaces in a step‐edge superconductor–normal metal–superconductor (SNS) Josephson junction could be investigated independently, due to contacts to the Au interlayer. The I–V characteristics of each superconductor–normal metal (SN) interface showed dc and ac Josephson‐like effects fitting well to a model, which takes into account the influence of proximity effect in the normal metal layer on the transport across the SN interface, and Andreev reflection at the interface. In the investigated junctions, both SN interfaces of the step SNS junctions had similar transparencies. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117810

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A reliable technique for wide band measurements of the spectral linewidth of superconducting oscillators integrated on‐chip with superconductor‐insulator‐superconductor (SIS) detectors has been developed. The spectral linewidth of flux‐flow oscillators (FFO) based on the unidirectional and viscous flow of magnetic vortices in a long overdamped Josephson tunnel junction was measured in the frequency range 250–580 GHz, and a linewidth as low as 200 kHz was obtained at 450 GHz. Also stable frequency locking of a FFO to very high (≤60th) harmonics of an external microwave reference source has been demonstrated. The proposed technique may improve the sensitivity, frequency resolution, and stability of the fully superconducting integrated submillimeter wave receiver. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117811

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The temperature dependence of the magneto‐optic sensitivity of gallium‐substituted yttrium iron garnets was measured at 1.3 &mgr;m and compared with a model based on molecular field theory. The model incorporates results of measurements of both the saturation magnetization and saturation Faraday rotation versus temperature. These measurements were analyzed in the context of molecular field theory to extract the fundamental molecular field coefficients and the magneto‐optical coefficients as functions of gallium content. The model and direct sensitivity measurements both indicate that the magneto‐optic sensitivity of garnet compositions with gallium substitution levels near 0.8 should exhibit a vanishing first‐order temperature sensitivity.©American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117812

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We present a technique for characterizing the magnetic state of a magnetic force microscopy (MFM) probe as a function of uniform external magnetic fieldH. A local magnetic field is generated by micron‐scale current carrying conductors and directly imaged by MFM. AsHalters the magnetic state of the probe, changes in image contrast yield componentwise measures of the tip’s net magnetic momentm, tip hysteresis loops and coercivities, and possible orientations (vertical vs lateral) of remanent statesmrused for most MFM imaging. Results are presented for a variety of thin‐film probes. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117813

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Ferromagnetic–insulator–ferromagnetic trilayer tunnel junctions show magnetoresistance (JMR) effects of about 14% or greater at room temperature. Much larger values of the JMR (100% or more) are observed when the actual tunneling resistance (RT) is comparable to electrode film resistance (RL) over the junction area. This latter apparent JMR is an artifact of the nonuniform current flow over the junction in the cross geometry of the electrodes. The ferromagnetic films were CoFe and Co or Ni0.8Fe0.2, and the tunnel barrier was AlN or Al2O3. These junctions show nonvolatile memory effects. The geometrically enhanced large JMR in junctions can be effectively used as magnetic sensors and memory elements. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117814

出版商:AIP    

年代:1996

数据来源: AIP