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16 Apr 1990

Volume 56, Issue 16, pp. 1515-1602

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Photon scanning tunneling microscope study of optical waveguides

Din Ping Tsai, Howard E. Jackson, R. C. Reddick, S. H. Sharp, and R. J. Warmack

Appl. Phys. Lett. 56, 1515 (1990); http://dx.doi.org/10.1063/1.103160 (3 pages) | Cited 44 times

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A novel technique, photon scanning microscopy, is shown to probe directly the evanescent field outside a planar and a channel waveguide. The decay lengths for these evanescent fields were measured and correspond well to the decay lengths of the evanescent fields calculated for each structure. Two‐dimensional scanning at constant intensity or constant height reveals lateral variations in these fields due to topographic changes, index of refraction inhomogeneities, or modal variations within the waveguide.
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07.60.Pb Conventional optical microscopes
42.79.Gn Optical waveguides and couplers
42.87.-d Optical testing techniques

Butt‐coupled InGaAs metal‐semiconductor‐metal waveguide photodetector formed by selective area regrowth

J. B. D. Soole, H. Schumacher, H. P. LeBlanc, R. Bhat, and M. A. Koza

Appl. Phys. Lett. 56, 1518 (1990); http://dx.doi.org/10.1063/1.103161 (3 pages) | Cited 5 times

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We report the monolithic integration of an InGaAs metal‐semiconductor‐metal Schottky barrier photodetector with a butt‐coupled InP/InGaAsP/InP waveguide, where the latter is formed by selective area regrowth using organometallic chemical vapor deposition. A fast pulse response (60–65 ps full width at half maximum, with no discernible tail) and a high quantum efficiency (∼80%) were observed for 1.3 μm guided light with the detector biased at 7 V. A thin InAlAs Schottky barrier enhancement layer limited the dark current to ∼28 nA at this bias.
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42.82.-m Integrated optics
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
85.60.Gz Photodetectors (including infrared and CCD detectors)
73.40.Sx Metal-semiconductor-metal structures

Injection‐locking characteristics of gain‐guided diode laser arrays with an ‘‘on‐chip’’ master laser

J. P. Hohimer, D. R. Myers, T. M. Brennan, and B. E. Hammons

Appl. Phys. Lett. 56, 1521 (1990); http://dx.doi.org/10.1063/1.103162 (3 pages) | Cited 6 times

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We report measurements of the injection‐locking characteristics of a high‐power continuous‐wave diode laser array with an on‐chip independently controlled master laser. This integrated injection‐locked array emits a near‐diffraction‐limited single‐lobed output beam at cw power levels up to 220 mW/facet. By controlling the current to the master laser, the single‐lobed output beam can be electronically steered over a far‐field angle of >1.7°. We also report preliminary studies of the coupling interaction in these integrated devices.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Mv Dye lasers

Measurement of cw HF laser resonant degenerate four‐wave mixing in an absorbing HF gas

J. G. Coffer, R. A. Chodzko, J. M. Bernard, and H. Mirels

Appl. Phys. Lett. 56, 1524 (1990); http://dx.doi.org/10.1063/1.103163 (2 pages) | Cited 2 times

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Continuous wave (cw) phase conjugation of a HF laser beam has been observed using resonant degenerate four‐wave mixing in a HF gas absorption cell. A HF laser was operated in the P1(8) transition to provide total (forward plus backward) pump beam and probe beam intensities of about 400 and 30 W/cm2, respectively, in the cell. Conjugate reflectivities were measured as a function of HF pressure and frequency detuning from line center. Reflectivities of the order of 10−4 were measured at HF gas pressures of the order of 2 Torr when the laser frequency was tuned near line center.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Semiconductor lasers with uniform longitudinal intensity distribution

Thomas Schrans and Amnon Yariv

Appl. Phys. Lett. 56, 1526 (1990); http://dx.doi.org/10.1063/1.103164 (3 pages) | Cited 6 times

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Power‐dependent nonuniform longitudinal intensity distribution leading to spectral and spatial instabilities is a major problem in semiconductor lasers. It is shown theoretically that a proper choice of the longitudinal distribution of the gain as well as that of the magnitude of the grating coupling coefficient will lead to a uniform intensity distribution in distributed feedback lasers. We also show that the widely used phase, rather than magnitude, control of the coupling coefficient cannot lead to a uniform intensity distribution when the facet reflectivities are zero.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.79.Dj Gratings
42.79.Gn Optical waveguides and couplers

Low‐loss AlGaAs optical rectangular waveguides at 830 nm

M. K. Hibbs‐Brenner and C. T. Sullivan

Appl. Phys. Lett. 56, 1529 (1990); http://dx.doi.org/10.1063/1.103165 (3 pages) | Cited 3 times

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Optical channel waveguides with rectangular cross section and losses less than 0.1 dB/cm at 830 nm have been fabricated in AlGaAs heterostructures grown by organometallic vapor phase epitaxy. The modal attenuation correlates with surface morphology for all waveguide widths and with sidewall roughness for narrow channels. Surface morphology and modal attenuation improve when a superlattice buffer layer is incorporated into the structure. The loss is also reduced when the arsenic source (arsine) is purified in‐line.
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42.79.Gn Optical waveguides and couplers
42.82.-m Integrated optics
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors

Intense charged‐particle emission in a diffuse vacuum discharge

H. Gundel and H. Riege

Appl. Phys. Lett. 56, 1532 (1990); http://dx.doi.org/10.1063/1.103166 (3 pages) | Cited 2 times

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The effects of plasma‐assisted emission of electrons from a cathode and of ions from an anode are used in experiments to generate intense particle beams in a vacuum gap. The plasma is produced by sputtering of the electrons and ions impinging on the electrode surfaces. When the initial electron beam, which is generated by ferroelectric emission, reaches a current density of about 1 A/cm2, a homogeneous vacuum discharge takes place provided an electric field of the order of 10 kV/cm is applied between the anode and the cathode. The vacuum gap is short circuited and the sum of the electron and ion beam currents is determined by the charging voltages and by the parameters of the external electric circuit. Beam currents of electrons and ions are extracted through holes or grids in the corresponding electrodes.
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29.25.Lg Ion sources: polarized
29.25.Ni Ion sources: positive and negative
29.25.Bx Electron sources
52.80.Vp Discharge in vacuum
79.20.Kz Other electron-impact emission phenomena

Ferroelectric inversion layers formed by heat treatment of proton‐exchanged LiTaO3

Kiyoshi Nakamura and Hiroshi Shimizu

Appl. Phys. Lett. 56, 1535 (1990); http://dx.doi.org/10.1063/1.103213 (2 pages) | Cited 41 times

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We report that a ferroelectric inversion layer can be formed in LiTaO3 by proton exchange in benzoic acid melts followed by heat treatment at temperatures just below the Curie point. It is demonstrated that the inversion layer appears at the −c surface for LiTaO3, whereas it appears at the +c surface for LiNbO3. The dependence of the inversion layer thickness on the conditions of proton exchange and heat treatment is also reported.
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77.80.Dj Domain structure; hysteresis
77.65.-j Piezoelectricity and electromechanical effects
81.40.Rs Electrical and magnetic properties related to treatment conditions

Effects of hydrogen on the photochemical unpinning of gallium arsenide

N. A. Ives, G. W. Stupian, and M. S. Leung

Appl. Phys. Lett. 56, 1537 (1990); http://dx.doi.org/10.1063/1.103167 (3 pages) | Cited 4 times

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Recent studies have shown that, after a preparative photowashing step, water, oxygen, and light must all be present in order to produce Fermi level unpinning of gallium arsenide surfaces. The in situ photoluminescence (PL) investigations in an optical flow cell reported here confirm this finding and show that the unpinning and subsequent repinning processes speed up with an increase in oxygen concentration in the water during photoluminescence measurements. When the water is saturated with hydrogen the surface unpins, although more slowly than if the water were saturated with oxygen, air, or nitrogen. In addition the surface remains unpinned for longer periods. The PL transient response data suggest that hydrogen is an active participant in surface photochemical reactions. A conceptual model is advanced that is consistent with the experimental data on pinning/unpinning processes on the GaAs surface.
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82.50.Bc Processes caused by infrared radiation
82.50.Hp Processes caused by visible and UV light
81.65.-b Surface treatments
73.20.At Surface states, band structure, electron density of states

Real time in situ observation of the film growth of hydrogenated amorphous silicon by infrared reflection absorption spectroscopy

Yasutake Toyoshima, Kazuo Arai, Akihisa Matsuda, and Kazunobu Tanaka

Appl. Phys. Lett. 56, 1540 (1990); http://dx.doi.org/10.1063/1.103168 (3 pages) | Cited 37 times

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The growth of hydrogenated amorphous silicon films on Al substrates in a flow reactor was studied using infrared reflection absorption spectroscopy. All three hydride species (SiHx , x=1–3) in the growing films were detected as stretching and bending absorption bands in P polarization spectra. The dominant absorption band, initially originating from higher hydrides, was shifted to lower wave numbers with an increase of film thickness. A steep rise in absorption intensity at the initial stage and a time delay in SiH emergence are discussed in terms of the enhancement of detection sensitivity in a hydrogen‐rich layer and the time needed for the formation of a bulk‐network structure, respectively.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.30.Hv Other nonmetallic inorganics

Selective deposition of aluminum from selectively excited metalorganic source by the rf plasma

Kazuya Masu, Kazuo Tsubouchi, Nobuyuki Shigeeda, Tatsuya Matano, and Nobuo Mikoshiba

Appl. Phys. Lett. 56, 1543 (1990); http://dx.doi.org/10.1063/1.103169 (3 pages) | Cited 13 times

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A selective method of depositing aluminum onto silicon was developed using trimethylaluminum and hydrogen as source gases. Trimethylaluminum was selectively decomposed into excited species through the well controlled radio frequency (13.56 MHz) excited hydrogen plasma of 0.03–0.06 W/cm3. Excited species were reacted on the silicon surface to produce aluminum without carbon incorporation at 230–260 °C. The thermally oxidized silicon dioxide line and space pattern and contact windows were successfully filled with selectively deposited 3000‐Å‐thick aluminum.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.10.Aj Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Anomalous silicon and tin doping behavior in indium phosphide grown by chemical beam epitaxy

P. J. Skevington, D. A. Andrews, and G. J. Davies

Appl. Phys. Lett. 56, 1546 (1990); http://dx.doi.org/10.1063/1.103170 (3 pages) | Cited 4 times

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Anomalous doping behavior of the most commonly used n‐type dopants, Si and Sn, has been observed in InP grown by chemical beam epitaxy from trimethylindium and cracked phosphine. In the case of Si, although incorporation is initially facile, the doping level decreases in successive runs. It is proposed that this decrease is due to the formation of SiC in the dopant cell. The behavior of Sn is more complex. In the range of Sn cell temperatures from 600 to 750 °C, incorporation is proportional to the elemental Sn vapor pressure. However, at low cell temperatures, 175–350 °C, anomalously large incorporations of Sn are observed. We attribute this behavior to the formation of a volatile metalorganic precursor within the Sn cell, its transport to the substrate, and subsequent decomposition and incorporation.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Ultraviolet‐induced defect creation in amorphous SiO2 exposed to an O2 plasma

R. A. B. Devine, J‐M. Francou, A. Inard, and J. Pelletier

Appl. Phys. Lett. 56, 1549 (1990); http://dx.doi.org/10.1063/1.103214 (3 pages) | Cited 8 times

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The creation of paramagnetic defects in plasma chemical vapor deposited amorphous SiO2 exposed to a rf oxygen plasma has been studied as a function of exposure time for two plasma power densities. Unpaired Si dangling bond defects (oxygen‐vacancy or oxygen‐vacancy like) have been observed in densities attaining ∼4×1017 cm−3 after more than 20 min exposure. These defect levels are equivalent to 10 Mrad of 60 Co γ radiation. Ultraviolet photons in the wavelength range 250≤λ≤300 nm are shown to be responsible for the defect creation. The 130 nm O∗ emission is found not to be important.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
76.30.Mi Color centers and other defects
61.72.sd Impurity concentration
61.72.sh Impurity distribution
61.72.sm Impurity gradients

Digital etching of GaAs: New approach of dry etching to atomic ordered processing

T. Meguro, M. Hamagaki, S. Modaressi, T. Hara, Y. Aoyagi, M. Ishii, and Y. Yamamoto

Appl. Phys. Lett. 56, 1552 (1990); http://dx.doi.org/10.1063/1.103171 (3 pages) | Cited 19 times

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A new approach to dry etching of GaAs, digital etching, has been demonstrated. In digital etching, the etchant and an energetic beam, which induces chemical sputtering at the surface, alternately impinge onto the surface. Electrons and Cl2 gas were used as the energetic beam and the etchant, respectively, in the present experiment. Etching rates of 1/3 monolayer/cycle, independent of Cl2 flux and electron current density, were obtained. The present results show that an inherent self‐limiting mechanism is involved and that the etching process is limited by the adsorption of etchant. This digital etching technique is expected to be applied to the fabrication of well‐defined quantum wire and quantum box structures.
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81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer
61.80.Fe Electron and positron radiation effects
61.80.Lj Atom and molecule irradiation effects

Modulation of quantized levels of GaAs/AlGaAs quantum wells by InAs monomolecular plane insertion

Michio Sato and Yoshiji Horikoshi

Appl. Phys. Lett. 56, 1555 (1990); http://dx.doi.org/10.1063/1.103172 (3 pages) | Cited 10 times

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GaAs/AlGaAs quantum well structures with InAs monomolecular planes are fabricated by flow‐rate modulation epitaxy. Photocurrent spectra of these structures are measured to investigate the effect of the InAs planes on the quantized levels. The InAs monomolecular plane inserted at the center of the well shifts the transition peak between the lowest levels (n=1 heavy hole and electron), but does not shift the transition peak between n=2 levels. The amplitude of the wave function for the electrons and holes on the n=2 levels is zero at the center of the well. Therefore, an InAs plane at the center does not modify the distribution of the n=2 carriers. When two InAs planes are inserted in a well and the distance between the two planes is varied, both n=1 and n=2 transition peaks are shifted. Measured spectra are well explained by a finite square well model calculation using the band parameters of GaAs and strained InAs.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Ey III-V semiconductors

Influence of the impurity concentration on charge carrier dynamics in GaAs films

A. Werner, M. Kunst, and T. D. Moustakas

Appl. Phys. Lett. 56, 1558 (1990); http://dx.doi.org/10.1063/1.103152 (3 pages)

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The influence of the silicon concentration on excess charge carrier kinetics in molecular beam epitaxy grown GaAs films has been studied by transient photoconductivity measurements with a contactless microwave conductivity technique. Several decay channels can be distinguished: an initial, fast second‐order decay more active in low impurity films and at high excitation intensities, and a slower decay component characterized by effective decay times ranging from 6 μs for low impurity samples and increasing decay times with increasing Si concentration. The initial, fast second‐order decay is attributed to electron‐hole recombination and is quenched by hole traps present at higher Si concentrations. In low impurity samples, the slower decay channel is ascribed to a deep electron trapping channel which can be saturated at higher excitation intensities. In high impurity samples, the decay time exceeds 100 μs and may be due to electron‐trapped hole transitions.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.40.+w Photoconduction and photovoltaic effects
72.80.Ey III-V and II-VI semiconductors

Focused ion beam channeling effects and ultimate sizes of GaAlAs/GaAs nanostructures

F. Laruelle, A. Bagchi, M. Tsuchiya, J. Merz, and P. M. Petroff

Appl. Phys. Lett. 56, 1561 (1990); http://dx.doi.org/10.1063/1.103153 (3 pages) | Cited 27 times

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We show that focused ion beam implantation of Ga into GaAlAs/GaAs quantum wells occurs much deeper than expected from theory of implantation into amorphous GaAs and that the lateral straggling is one order of magnitude smaller than predicted by the same theories. We show that channeling is the main mechanism involved in these effects. The small probe size achieved with the focused ion beam is thus preserved 200 nm below the surface.
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61.85.+p Channeling phenomena (blocking, energy loss, etc.)
78.60.Hk Cathodoluminescence, ionoluminescence
61.72.U- Doping and impurity implantation
68.35.Dv Composition, segregation; defects and impurities

Nanometer resolution in luminescence microscopy of III‐V heterostructures

D. L. Abraham, A. Veider, Ch. Schönenberger, H. P. Meier, D. J. Arent, and S. F. Alvarado

Appl. Phys. Lett. 56, 1564 (1990); http://dx.doi.org/10.1063/1.103154 (3 pages) | Cited 86 times

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In a scanning tunneling microscope experiment, the luminescence induced by the recombination of holes with electrons tunneling into cleaved (110) GaAs/AlGaAs heterostructures is used to image the interface region with nanometer resolution.
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78.55.Cr III-V semiconductors
73.40.Gk Tunneling
78.30.Fs III-V and II-VI semiconductors
07.60.Pb Conventional optical microscopes

Planar stress relaxation in solid phase epitaxial CaF2 films grown on (111)Si by in situ rapid isothermal processing

R. Singh, A. Kumar, R. P. S. Thakur, P. Chou, J. Chaudhuri, V. Gondhalekar, and J. Narayan

Appl. Phys. Lett. 56, 1567 (1990); http://dx.doi.org/10.1063/1.103215 (3 pages) | Cited 6 times

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Planar strain in CaF2 films on (111) Si substrate has been measured by an x‐ray double‐crystal diffraction technique using rocking curves. The films grown by a solid phase epitaxial approach using in situ rapid isothermal processing are almost free of tensile planar strain, and free from defects as observed by the transmission electron microscope diffraction pattern.
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81.15.Np Solid phase epitaxy; growth from solid phases
68.55.-a Thin film structure and morphology
68.35.Gy Mechanical properties; surface strains

Study of cooling of hot carriers and intervalley scattering in In0.53Ga0.47As by subpicosecond Raman scattering

D. S. Kim and P. Y. Yu

Appl. Phys. Lett. 56, 1570 (1990); http://dx.doi.org/10.1063/1.103133 (3 pages) | Cited 9 times

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Subpicosecond laser pulses have been used to excite and probe photoexcited hot‐electron plasma in In0.53 Ga0.47 As by Raman scattering. Hot‐electron temperatures have been measured as a function of the length of subpicosecond pulses. Cooling of the hot electrons is compared with a model calculation in which the cooling mechanism is dominated by intervalley scattering. The Γ to L intervalley deformation potential in In0.53 Ga0.47 As was determined to be around 3.5×108 eV/cm.
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78.47.-p Spectroscopy of solid state dynamics
78.30.Fs III-V and II-VI semiconductors
71.35.-y Excitons and related phenomena

Preparation of the Tl‐Ba‐Ca‐Cu‐O thick film by processing the screen‐printed Ba‐Ca‐Cu‐O film in Tl2O3 vapor

Lingwen Zeng, Zijiang Zhao, Li Zhang, Hongqi Chen, Zhengnan Qian, and Daiming Wu

Appl. Phys. Lett. 56, 1573 (1990); http://dx.doi.org/10.1063/1.103216 (3 pages) | Cited 4 times

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Superconducting Tl‐Ba‐Ca‐Cu‐O thick films on yttria‐stablized zirconia (YSZ) substrates have been obtained by processing the screen‐printed Ba‐Ca‐Cu‐O films in Tl2O3 vapor. The properties of the films are found to be dependent sensitively on the Tl2O3 vapor processing conditions. The best film with a zero resistance Tc at 115 K was heated in Tl2O3 vapor at 890 °C for 4 min followed by cooling to 300 °C at a rate of 2–3 °C/min. X‐ray diffraction and energy dispersive x‐ray studies indicated that the films are polyphase, but the high Tc phase Tl2Ba2Ca2Cu3Ox is predominant.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates
74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition

Tailored thin films of a superconducting Bi‐Sr‐Ca‐Cu oxide prepared by incorporation of exotic atoms—control of the distance between CuO2 layers

Hitoshi Tabata, Osamu Murata, Tomoji Kawai, and Shichio Kawai

Appl. Phys. Lett. 56, 1576 (1990); http://dx.doi.org/10.1063/1.103217 (3 pages) | Cited 13 times

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A layer‐by‐layer successive deposition method utilizing laser ablation has been applied to the site‐selective incorporation of +1, +2, and +3 ions at the Ca and Sr site of Bi2Sr2Ca1Cu2O8 superconducting films. The replacement of Ca by larger ions increases the lattice parameter c and Tc simultaneously, while the replacement of Sr does not. These changes are explained by structure models of Bi2Sr2Ca1Cu2O8, and the correlation between Tc and the lattice parameter c is explained on the basis of the distance between CuO2 layers, indicating the importance of the interaction among CuO2 layers.
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74.70.-b Superconducting materials other than cuprates
74.78.-w Superconducting films and low-dimensional structures
61.72.up Other materials
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Bulk BiPbSrCaCuO rf SQUIDs operating up to 101 K

Yi Zhang, Yunhui Xu, and C. Heiden

Appl. Phys. Lett. 56, 1579 (1990); http://dx.doi.org/10.1063/1.103134 (3 pages) | Cited 2 times

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rf superconducting quantum interference devices (SQUIDs) of bulk Bi1.4Pb0.6Sr2Ca2Cu3Ox samples have been fabricated using an adjustable break junction and operated from 4.2 to 101 K. An adjustable break junction is used as weak link whose critical current can be varied to obtain the optimum signal at each given temperature. These SQUIDs can be reproducibly operated after many thermal cycles and moisture‐drying processes. Flux noise spectra as function of both of frequency and temperature have been measured. The typical values of flux noise and energy resolution at a frequency of 200 Hz and 77 K are ∼2×10−4 ϕ0/(Hz)1/2 and ∼8.6×10−28 J/Hz, respectively, which are comparable to that of bulk YBa2Cu3O7−y rf SQUIDs.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
74.40.-n Fluctuation phenomena
74.50.+r Tunneling phenomena; Josephson effects

Effect of Lorentz force on thermally activated processes of flux lines in a Bi‐Sr‐Ca‐Cu‐O film

S. Takamura, T. Hoshiya, and T. Aruga

Appl. Phys. Lett. 56, 1582 (1990); http://dx.doi.org/10.1063/1.103135 (3 pages) | Cited 1 time

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The temperature dependence of electric voltage in a Bi‐Sr‐Ca‐Cu‐O film is measured for various electric currents and magnetic fields perpendicular and parallel to the film plane, in which the direction of the electric current is both perpendicular and parallel to the magnetic field. The thermally activated flux motion is deduced from the logarithmic dependence of voltage against l/T and the relation between the transition temperature and the Lorentz force. The relation between the activation energy, the transition temperature, the Lorentz force, and the volume to hop over energy barrier is discussed.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.78.-w Superconducting films and low-dimensional structures
74.25.Sv Critical currents
74.70.-b Superconducting materials other than cuprates

Origin of the silver doping effects on superconducting oxide ceramics

Yasumichi Matsumoto, Jukichi Hombo, Yoshiaki Yamaguchi, Minoru Nishida, and Akira Chiba

Appl. Phys. Lett. 56, 1585 (1990); http://dx.doi.org/10.1063/1.103218 (3 pages) | Cited 24 times

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The origin of silver doping effects on Y‐Ba‐Cu‐O superconducting ceramics, such as a high‐temperature shift of the point at zero resistivity in resistivity measurements and an increase in critical current density, was sought by transmission electron microscopy observations. Sintering was strongly promoted together with suppression of the formation of the liquid phase in the grain boundaries by silver. Consequently, the liquid phase, which is not a superconductor, was not present in almost all the grain boundaries of the silver‐doped ceramics, while this phase was present in almost all the grain boundaries in pure ceramics.
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74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.70.-b Superconducting materials other than cuprates
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
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