摘要:

The relative densities of high‐voltage stress‐generated traps near the anode and cathode in 10‐nm‐thick silicon oxides have been measured after both positive and negative gate voltage stressing. The density of traps near the stress anode and cathode were approximately equal after negative gate voltage stressing. The density of traps near the stress cathode was higher than near the stress anode after positive gate voltage stressing. These results implied that impact ionization near the anode was not a significant generator of traps in 10‐nm‐thick oxides. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361251

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The evolution of microstructure during Au‐mediated solid phase epitaxial growth of a SixGe1−xalloy film on Si(001) was investigated byinsitusheet resistance measurements, x‐ray diffraction, conventional and high‐resolution transmission electron microscopy, energy dispersive x‐ray spectroscopy, and Rutherford backscattering spectrometry. Annealing amorphous‐Ge/Au bilayers on Si(001) to temperatures below 120 °C caused changes primarily in the microstructure of the Au film. Near ≊130 °C, Ge from the top layer diffused and crystallized along the grain boundaries of Au. The Ge that had reached the Au/Si (001) interface mixed with Si from the substrate, to form epitaxial SixGe1−xislands on Si (001). Si from the substrate had dissolved into Au before entering the growing epitaxial islands. Meanwhile, the Au that was displaced by Ge that filled the Au grain boundaries, diffused into the top layer along columnar voids in the amorphous Ge film. With increasing temperature, more Au was displaced to the top by the flux of Ge towards the substrate, facilitating further epitaxial growth and the coalescence of epitaxial SixGe1−xislands. At 310 °C, the initial Au film was displaced completely to the top by a laterally continuous SixGe1−xepilayer of uniform composition (x≊0.15). The epilayer thickness was limited by that of the initial Au film. Twins and residual amounts of Au trapped near the SixGe1−x/Si(001) interface were the predominant defects observed in the completely strain‐relaxed SixGe1−xepilayer. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361252

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have applied the 6×6k⋅pHamiltonian to calculate the valence subband structure ofp‐type GexSi1−xquantum wells. When the sheet density of carriers is 5×1012cm−2or less, normal incident radiation absorption in thep‐type GexSi1−xquantum well is due to the inter‐valence band mixings. Subbands become more independent when their energy separations are high, so that high‐energy optical absorption is weak. The transition from ground subband to the first excited subband contributes mostly to the normal incident radiation absorption, as demonstrated in many measurements. The work can be extended to design and optimizep‐type GexSi1−xquantum well infrared detector. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361253

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The electronic structure of SiC/SiO2interfaces was studied for different SiC polytypes (3C, 4H, 6H, 15R) using internal photoemission of electrons from the semiconductor into the oxide. The top of the SiC valence band is located 6 eV below the oxide conduction band edge in all the investigated polytypes, while the conduction band offset at the interface depends on the band gap of the particular SiC polytype. In the energy range up to 1.5 eV above the top of the SiC valence band, interface states were found. Their electron spectrum is similar to that ofsp2‐bonded carbon clusters in diamond‐likea‐C:H films suggesting the presence of elemental carbon at the SiC/SiO2interfaces. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361254

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A method is described for extracting bulk minority carrier lifetimes and surface recombination velocities from insulator‐semiconductor structures. Recombination in the bulk and at the two surfaces of the wafer are distinguished by using the wavelength dependence of the penetration depth of the incident light flux. Pulse modulated light from various wavelength light‐emitting diodes is used to create excess minority carrier holes which are collected in the depletion region of an inverted surface. The spectral dependence of the resulting photocurrents can then be used to determine the surface recombination velocities and the bulk lifetime. A model is described which provides relationships between the bulk minority carrier lifetime, the surface recombination velocities, the absorption coefficient of the incident light, and the resulting capacitive current. The experimental values of lifetime and surface recombination velocity are combined to obtain an effective lifetime which is in good agreement with a combined lifetime obtained from the photoconductive decay technique. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361255

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The structural properties of superconducting (Bi,Pb)2Sr2Ca2Cu3O10–Ag (2223) tapes have been measured using synchrotron x‐ray scattering techniques. The x‐ray photon energy was tuned just below the silverKabsorption edge so the penetration depth was large, which allowed the measurements to be performed in a transmission geometry without removing the silver cladding. Analysis of the peaks in 2&thgr; scans indicates that residual (Bi,Pb)2Sr2CaCu2O8(2212) superconductor starting material is present in all samples studied. The amount of 2212 varied widely among the tapes, and was not homogeneous along the length of each individual tape. Residual 2212 content increased near the ends of most samples, suggesting that 2223 phase development is sensitive to whether the superconducting material is encased in silver or not. The bulkc‐axis alignment was measured in ∼100 mono‐ and multifilament samples, and correlations betweenc‐axis alignment and current carrying capacity at 77 K were found. Multifilament samples generally had better alignment than monofilament samples. Thec‐axis alignment along the length of the tapes was uniform, and the superconducting material within ∼1 &mgr;m of the Ag was better textured than the bulk of the sample. Intermediate pressings were directly shown to have an adverse affect onc‐axis alignment. Finally, the evolution of texture and phase development was examined in a series of samples annealed for varying times. The 2212 starting material acquired the finalc‐axis alignment state after brief heating times, and only after much longer heating times did the 2212 transform into the 2223 phase. These results and their implications for improving processing procedures are discussed. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362695

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The ac losses of NbTi multifilamentary superconducting wires with a copper matrix were measured using a sensitive calorimetric method. The wire samples, which have filament diameters in the micrometer range and interfilament spacings of a few tenths of a micrometer, exhibit a strong proximity effect. The measured power loss at a constant ac field amplitude and frequency showed an unexpected time dependence on a very long time scale of hours, compared to the ac field cycle time being in the millisecond range. The measured loss vs time curves were found to depend sensitively on amplitude and frequency of the ac field, and in the way the ac field was switched on. The effect can be rather large, changes of losses by up to 60% were found. Losses can increase or decrease with time depending on the structure of the sample. As an independent check losses were also measured by a magnetization method. The results were in very good agreement with the calorimetric measurement. The effect of time dependent losses is qualitatively explained by the slow decay of proximity currents which are induced when the ac field is switched on. They create a time dependent bias magnetization, which influences the ac losses. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361256

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The effective magnetoelastic (ME) coupling coefficientsBeffof polycrystalline Ni79Fe21and Ni films have been reported as functions of thicknesst.Beffwas observed to have a thickness‐independent bulk term,Bb, and a thickness‐dependent surface term,Bs/tconsistent with the Ne´el model. For thickness below 50 A˚ the surface term is important; it can change the sign of the effective ME coupling constant and dramatically increase its magnitude. We expect that the surface ME coupling we observe in polycrystalline thin films may be a combination of the intrinsic Ne´el surface effect and extrinsic microstructure effects. Our transmission electron microscopy, Auger depth profiling, and atomic force microscopy rule out film discontinuity and compositional gradients as significant sources of the surface ME effect. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361223

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The magnetic properties of a series of Ce2Fe17−xAlxsolid solutions withxequal to 0.00, 0.88, 2.06, 2.81, 3.98, 5.15, 6.08, 7.21, 8.20, 9.08, 9.84, and 10.62 have been studied by magnetic measurements, neutron diffraction, and Mo¨ssbauer spectroscopy. The compounds crystallize in the rhombohedral Th2Zn17‐type structure. Magnetization studies indicate that the Curie temperature increases uniformly from 238 K for Ce2Fe17to 384 K for Ce2Fe14Al3and then decreases at higher aluminum content. Powder neutron diffraction results, obtained at 295 K, indicate that aluminum avoids the 9dsite for allxvalues and preferentially occupies the 18hsite at low aluminum content. Aluminum shows a marked preference for the 6csite forx≳6. The room‐temperature iron magnetic moments increase fromx=0 to 2 and then decrease forx≳2. The Mo¨ssbauer spectra have been fit with a binomial distribution of the near‐neighbor environments in terms of a maximum hyperfine field,Hmax, for an iron with zero aluminum near neighbors, and a decremental field, &Dgr;H, per aluminum near neighbor. The compositional dependence of the decremental field indicates the influence of aluminum on the long‐range magnetic ordering in the compound.The compositional dependence of the weighted average maximum hyperfine fields and the weighted average isomer shifts in Ce2Fe17−xAlxmay be understood in terms of a mixing of the 3dconduction band electrons with the 3pvalence band electrons of aluminum, a mixing which is more extensive than that associated with silicon in the Ce2Fe17−xSixsolid solutions. We conclude that this mixing has a larger influence on the magnetic properties of these solid solutions than does the presence of a short iron–iron bond or the expansion or contraction of the lattice parameters and unit cell volume. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361257

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The angular dependence of surface magnetic Barkhausen noise (MBN) with flux densities up to 1.7 T on eight different samples of oriented 3% Si–Fe steel laminate was investigated. On two of the samples encircle MBN measurements were performed. MBN energy values were obtained by integrating the square of the MBN voltage signal with respect to time. The angular variation of the MBN energy signal was modeled by considering anisotropic internal fields that moderate 180° domain wall motion and the local eddy current field interactions between spatially correlated Barkhausen events. The eddy current field interactions arising between 180° domain walls that lie along the sample’s primary easy axis direction were represented by a parameter, &agr;′. &agr;′ had a cos &thgr; angular dependence where &thgr; is the angle of the applied sweep field with respect to the sample rolling direction. The angular averaged MBN energy signal, ⟨Energy⟩, was evaluated and compared with core losses measured using the standard Epstein technique at 1.5 T. Surface MBN measurements on samples with higher ⟨Energy⟩ demonstrated lower core loss. This was associated with a larger proportion of microscopic eddy currents generated parallel to the sample plane which were, therefore, uncoupled from macroscopic eddy currents generated by the bulk magnetization of the sample. Larger surface ⟨Energy⟩ signals were identified with a finer domain wall structure. For samples with a nonzero &agr;′, the core loss was observed to decrease with increasing &agr;′ magnitude. This was interpreted as a result of a reduction of microscopic eddy currents arising from an increase in interactions between simultaneously moving 180° domain walls. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361258

出版商:AIP    

年代:1996

数据来源: AIP