摘要:

A numerical procedure for the calculation of the electron tunneling current through an arbitrary potential profile has been developed. It involves subdividing the profile into a number of strips for which a linear approximation of the potential is appropriate. A solution of the Schro¨dinger equation in the form of Airy functions is obtained. These functions are linked through boundary conditions at the interface of the strips. An expression for the transmission coefficient of the structure is obtained. The approach is found to accelerate the calculation of the electrical characteristic of resonant tunneling devices. An analysis is performed of tunneling through parabolic quantum‐well and half‐parabolic quantum‐well structures in the presence of an electric field. The room‐temperature current‐voltage characteristic for the half‐parabolic quantum‐well structure is calculated and is found to be rectifying with multiple peaks and regions of negative differential resistance. It is also found to have a relatively high peak‐to‐valley ratio and high peak current density.

ISSN:0021-8979    

DOI:10.1063/1.345423

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The resistivity and temperature coefficient of resistivity of copper and nickel thin films used as high‐density interconnections in hybrid packages have been measured in the temperature interval 298–723 K. The effects of film thickness, deposition conditions, and postdeposition anneal were analyzed in detail. Minimum as‐deposited resistivities approximately 18% and 80% above bulk values could be achieved under optimized deposition conditions for 1‐&mgr;m‐thick copper and nickel films, respectively. Contributions to the resistivity values attributable to electron scattering at phonons, surfaces, impurities, grain boundaries, and intragranular defects were also established. Although subsequent annealing had little impact on the resistivity of copper, a significant reduction in the resistivity of nickel was observed, due primarily to dislocation sinking. Lastly, the relationship of resistivity to the temperature coefficient of resistivity for both metal films was found to be in agreement with Matthiessen’s rule.

ISSN:0021-8979    

DOI:10.1063/1.345424

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The effect of rapid thermal annealing on the composition, structure, andI‐Vcharacteristics of Al(0.8% Si)/Ti:W/a‐Si contacts was studied. It was established that heat treatments in temperatures ranging between 300 and 500 °C for a time span of 10 s led to grain boundary diffusion of Si and Al through the Ti10W90layer. Subsequently, Si diffused into the Al film while Al penetrated into the amorphous Si. No silicides or intermetallic compounds were observed to form as a result of the rapid heat treatments. The electrical measurements showed that theI‐Vcurve in the forward bias is identical to that of the reversed bias. The electrical resistance of the contacts increased as a result of a rise in the heat treatment temperature. A model of electrical conductivity in amorphous semiconductors was applied to explain the electrical behavior of the contacts.

ISSN:0021-8979    

DOI:10.1063/1.345425

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Data are presented on the role of the InAs/AlSb interface in determining the electron transport in AlSb/InAs/AlSb quantum wells grown by molecular‐beam epitaxy. Because both anion and cation change across an InAs/AlSb interface, it is possible to grow such wells with two different types of interfaces, one with an InSb‐like bond configuration, the other AlAs‐like. Electron mobility and concentration were found to depend very strongly on the manner in which the quantum well’s interfaces were grown, indicating that high mobilities are seen only if the bottom interface is InSb‐like. An As‐on‐Al sites antisite defect model is postulated for bottom AlAs‐like interfaces. Such antisites were used in subsequent samples as donors in modulation‐doped high‐mobility InAs/AlSb quantum wells.

ISSN:0021-8979    

DOI:10.1063/1.345426

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A process for the fabrication of high‐quality, all‐refractory Josephson junctions of the type Nb/SixNy/Nb is described in detail. The junctions have been fabricated using the selective niobium anodization process with a tunnel barrier consisting of an amorphous Si film converted to its nitride by the application of a rf plasma of nitrogen. An attractive feature of these junctions is their comparably low specific capacitanceC/A=3.9±0.1 &mgr;F/cm2(forJc=6 A/cm2). Junctions of this type having critical current densities up toJc=2000 A/cm2andVm=16 mV have been fabricated. Excellent magnetic field threshold curves have also been observed for these junctions, indicating that the critical current density is very uniform.

ISSN:0021-8979    

DOI:10.1063/1.345432

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

This paper describes the effect of Sn additions to PbMo6S8ribbons. These ribbons are produced via a vapor‐transport technique. Small amounts of Sn in Sn1−xPbxMo6S8alloy ribbons provide a significant (∼10×) increase inJcat high fields over that obtained with PbMo6S8alone. Critical current densities of 1×104A/cm2at 4.2 K near 20 T have been achieved for compositions withxnear 0.5. The lowJc’s in PbMo6S8appears to be related to the presence of a large fraction of a nonsuperconducting triclinic phase resulting from a partial phase transition at cryogenic temperatures. This phase transition is partially suppressed with Sn additions, resulting in an improved performance.

ISSN:0021-8979    

DOI:10.1063/1.345433

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The magneto‐optical Faraday effect has been used to observe the penetration of magnetic flux into sintered YBa2Cu3O7−&dgr;. In addition, measurements of the magnetic polarization are performed with a SQUID magnetometer. The magneto‐optical Faraday effect shows an inhomogeneous penetration of the magnetic flux into the sample. In a first step the flux penetrates into the intergranular regions and in a second step into single grains separately. A spatial gradient of the flux density within each grain is built up, indicating pinning forces. In the remanent state in each grain trapped flux is observed. The measured magnetization curves show good agreement with the magneto‐optical investigations of the flux penetration.

ISSN:0021-8979    

DOI:10.1063/1.345434

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We have investigated the optical response ofc‐axis oriented crystalline Y1Ba2Cu3O7−xthin films (bridge and meander devices) on strontium titanate and MgO substrates. cw optical response to a He‐Ne laser radiation (wavelength of 0.63 &mgr;m) was primarily bolometric. The pulsed optical response was studied withQ‐switched and mode‐lockedQ‐switched short pulses from a Nd:YAG laser at the wavelength of 1.06 &mgr;m. We identify two distinct components contributing to the pulsed optical response: a nonbolometric (as fast as 1 ns) and a bolometric component (several ns). The bolometric component is strong at temperatures in the vicinity of the transition region to the normal state. The nonbolometric component is dominant at temperatures below the transition region showing weak temperature dependence and a linear dependence on the bias current. These results are discussed using the flux motion model and also electron‐phonon scattering relaxation dynamics of nonequilibrium superconductors based on the theory of Bardeen‐Cooper‐Schrieffer. The results suggest that with proper optimization of device parameters (geometry, critical current density, etc.) sensitive bolometers and high‐speed detectors covering a broad electromagnetic spectrum (visible and infrared) may be developed.

ISSN:0021-8979    

DOI:10.1063/1.345435

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We have achieved ablation of Bi‐Sr‐Ca‐Cu oxide from single targets of superconducting pellets by CO2‐laser pulses of l ms length to grow superconducting thin films. Upon annealing, the 6000‐A˚ thin films have aTc(onset) of 90 K and zero resistance at 78 K. X‐ray diffraction patterns indicate the growth of single‐phase thin films. This technique allows growth of uniform single‐phase superconducting thin films of lateral area greater than 1 cm2.

ISSN:0021-8979    

DOI:10.1063/1.345406

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Aggregation in sterically stabilized Fe3O4ferrofluids has been studied with the small‐angle neutron scattering technique. The influence on the aggregation of the particle volume fraction, varying between 0.02 and 7 vol % Fe3O4, and the influence of an applied magnetic field is examined. Contrast variation enabled the scattering of particles and surfactants to be measured independently. The particle size distribution derived from the scattering is in good agreement with the field dependence of the magnetization and the optical anisotropy. From the anisotropy in the neutron scattering patterns of fluids subjected to a magnetic field of 0.10 T perpendicular to the neutron beam, it is derived that at all volume fractions below 1 vol % Fe3O4most of the particles are located in small chainlike aggregates oriented parallel to the field direction. Larger, three‐dimensional aggregates arise at higher volume fractions, both in the applied field and in zero field. The interparticle distance within an aggregate corresponds to surface‐to‐surface contact of the surfactant coatings.

ISSN:0021-8979    

DOI:10.1063/1.345407

出版商:AIP    

年代:1990

数据来源: AIP