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20 Oct 1997

Volume 71, Issue 16, pp. 2227-2397

Page 2 of 3 Pages Previous Page Next Page | Jump to Page

Surface roughening by electron beam heating

D. Grozea, E. Landree, and L. D. Marks

Appl. Phys. Lett. 71, 2301 (1997); http://dx.doi.org/10.1063/1.120055 (3 pages) | Cited 4 times

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The effect of electron beam heating during the preparation of clean silicon surfaces suitable for epitaxial studies in ultrahigh vacuum conditions was investigated using surface chemical characterization techniques and transmission electron microscopy. The electron beam irradiation produced a disordered surface on the incident side of the sample and well-ordered monoatomic steps on the other surface, even at electron energies as low as 3 keV. These results have significant implications for epitaxial thin film growth. © 1997 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.65.-b Surface treatments
61.80.Fe Electron and positron radiation effects
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Misfit dislocations and stresses in GaN epilayers

Junyong Kang and Tomoya Ogawa

Appl. Phys. Lett. 71, 2304 (1997); http://dx.doi.org/10.1063/1.120056 (3 pages) | Cited 6 times

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GaN epilayers nitridated initially for different times have been investigated by light scattering tomography (LST) and Raman scattering. In the LST images of the plan-view epilayers, the light scattering defects mainly distribute in 〈1120〉 directions. The density of the defects is lower in epilayer nitridated initially for a longer time. The defects are considered to be the straight threading edge dislocations on {1100} planes. The Raman shift of E2 mode is larger in the sample initially nitridated for a longer time. Our results show that the misfit between the GaN epilayer and the Al2O3 substrate is more unfavorably accommodated by the threading edge dislocations in the epilayers initially nitridated for a longer time. © 1997 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
78.35.+c Brillouin and Rayleigh scattering; other light scattering
68.60.Bs Mechanical and acoustical properties
78.66.Fd III-V semiconductors

Molecular dynamics studies of interacting hydrogenated Si(001) surfaces

D. Conrad, K. Scheerschmidt, and U. Gösele

Appl. Phys. Lett. 71, 2307 (1997); http://dx.doi.org/10.1063/1.120057 (3 pages) | Cited 4 times

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The interaction of hdyrogenated Si(001) surfaces is studied by means of molecular dynamics using an empirical potential. Above a certain critical external force covalent bonds may be formed between the surfaces even at room temperature, leaving a hydrogenated interface. The critical force is related to the assumptions of the molecular dynamics, thus scaling with the potential, heat transfer, boundary conditions, and the weak long-range interaction omitted. Below this critical force, the hydrogen–hydrogen interactions prevent covalent bonding. © 1997 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
61.50.Lt Crystal binding; cohesive energy

Internal oxidation of low dose separation by implanted oxygen wafers in different oxygen/nitrogen mixtures

Per Ericsson and Stefan Bengtsson

Appl. Phys. Lett. 71, 2310 (1997); http://dx.doi.org/10.1063/1.120058 (3 pages) | Cited 6 times

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The electrical properties and the structure of the buried oxide in low dose SIMOX wafers were investigated after 1200 °C oxidation in different diluted oxygen ambients. The thickness of the silicon dioxide grown on top of the thin silicon films was the same for all samples. Correlating the breakdown field and the surface structure of the buried oxide with process conditions showed that the oxidation time was the key parameter for improving oxide performance while the oxygen partial pressure only played a minor role. We suggest that saturation of atomic oxygen in the thin silicon film during oxidation is responsible for this behavior. © 1997 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.72.uf Ge and Si
85.40.Ry Impurity doping, diffusion and ion implantation technology
68.35.B- Structure of clean surfaces (and surface reconstruction)
77.22.Jp Dielectric breakdown and space-charge effects
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Lattice expansion of Ca and Ar ion implanted GaN

C. Liu, B. Mensching, K. Volz, and B. Rauschenbach

Appl. Phys. Lett. 71, 2313 (1997); http://dx.doi.org/10.1063/1.120059 (3 pages) | Cited 44 times

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The 180 keV Ca+ and Ar+ ions were homogeneously implanted in GaN at temperature of liquid nitrogen. High resolution x-ray diffraction was used to monitor the change of GaN (0002) peak with the dose ranging from 5×1012 to 1×1016 cm−2. It has been found that with increasing dose a new peak beside the GaN (0002) peak appears, grows up, and gradually shrinks until disappearance with arising of the amorphous peak, accompanied with a shift towards smaller angles. The difference between Ca+ and Ar+ implantation is discussed. Expansion of GaN crystal lattice due to Ca+ and Ar+ implantation accounts for this phenomenon and is confirmed by TEM results. © 1997 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors

Landau level formation in semiconductor quantum dots in a high magnetic field

S. Nomura, L. Samuelson, M.-E. Pistol, K. Uchida, N. Miura, T. Sugano, and Y. Aoyagi

Appl. Phys. Lett. 71, 2316 (1997); http://dx.doi.org/10.1063/1.120070 (3 pages) | Cited 10 times

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Landau level formations have been observed in the photoluminescence spectra of highly optically populated InP strained self-organized quantum dots in between barriers of In0.5Ga0.5P at a high magnetic field. The results clearly show the evolution of the discrete states caused by 3D confinement at 0 T into Landau level-like structures at 40.9 T. © 1997 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
71.70.Di Landau levels

Quantum-size effects in the titanosilicate molecular sieve

Enzo Borello, Carlo Lamberti, Silvia Bordiga, Adriano Zecchina, and Carlos Otero Areán

Appl. Phys. Lett. 71, 2319 (1997); http://dx.doi.org/10.1063/1.120060 (3 pages) | Cited 42 times

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The recently synthesized Engelhard titanosilicate (ETS-10) represents a material which contains in the structure well defined atomic ⋯O–Ti–O–Ti–O⋯ quantum wires embedded in a highly insulating siliceous matrix. We report and discuss the UV-Vis spectrum of this material and compare the experimentally determined optical band gap with the results predicted by simple modeling of a titanium oxide semiconductor wire unidimensionally confined by an infinite potential barrier. © 1997 American Institute of Physics.
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73.50.Mx High-frequency effects; plasma effects
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Le Other inorganic semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Li Other semiconductors
78.40.Fy Semiconductors

Effect of total deposition pressure on the structure of polycrystalline-silicon films

T. I. Kamins and A. Fischer-Colbrie

Appl. Phys. Lett. 71, 2322 (1997); http://dx.doi.org/10.1063/1.120061 (3 pages) | Cited 1 time

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The effect of total deposition pressure on the structure of chemically vapor deposited polycrystalline-silicon films was examined over the pressure range from 10–600 Torr using thermal decomposition of SiH4 in a hydrogen carrier gas in the 625–675 °C temperature range in a cold-wall, lamp-heated reactor. The temperature and deposition rate were kept constant for each set of experiments to isolate the effect of hydrogen on the surface diffusion of the silicon species. Both the amorphous-to-polycrystalline transition and the dominant crystal orientation depend on the total deposition pressure; however, the dependence is only moderate. Differences in gas purity and system integrity between different reactors also play a strong role in controlling the structure. © 1997 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
68.35.Fx Diffusion; interface formation

Formation of InAs/GaAs quantum dots by molecular beam epitaxy: Reversibility of the islanding transition

Hao Lee, Roger R. Lowe-Webb, Weidong Yang, and Peter C. Sercel

Appl. Phys. Lett. 71, 2325 (1997); http://dx.doi.org/10.1063/1.120062 (3 pages) | Cited 38 times

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We report a study of the dynamics of coherent island formation in InAs/GaAs films grown by molecular beam epitaxy. A comparison of the temperature dependence of the critical layer thickness for islanding between the migration-enhanced and the continuous growth modes confirms that surface adatom diffusion and indium desorption are the controlling processes which determine the variation of the measured critical layer thickness with temperature. We find that under conditions in which indium desorption is significant, the islanding transition is reversible, which provides a new way to study the dynamics of the islanding transition. Applying this technique, we find that the size distribution of the three-dimensional islands evolves into a bimodal distribution during the reverse process. © 1997 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
68.35.Fx Diffusion; interface formation

Effects of isolation materials on facet formation for silicon selective epitaxial growth

H.-C. Tseng, C. Y. Chang, F. M. Pan, J. R. Chen, and L. J. Chen

Appl. Phys. Lett. 71, 2328 (1997); http://dx.doi.org/10.1063/1.120033 (3 pages) | Cited 8 times

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Effects of isolation materials on facet formation for low temperature Si selective epitaxial growth (SEG) using Si2H6 have been demonstrated by ultrahigh vacuum-chemical molecular epitaxy (UHV-CME) system. The activation energy of the Si epitaxial growth is 47.35 Kcal/mol. The isolation material includes silicon nitride, wet oxide, and tetraethylorthosilicate (TEOS) oxide. Different isolation materials have different faceting behaviors for the Si epilayer. A silicon nitride mask and a wet oxide mask result in a preferred faceting plane of (111) and (311), respectively. Using a TEOS oxide mask, we obtain a low temperature Si SEG layer without facet and twin formation. The preferred faceting plane orientation for different isolation materials is ascribed to the difference in the interface free energy between the Si layer and the isolation material. © 1997 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
61.72.Mm Grain and twin boundaries
65.20.-w Thermal properties of liquids
65.40.gd Entropy

Evidence of a blue shift in near surface ultra thin InAs/InP island like quantum wells

J. M. Sallese, J. F. Carlin, M. Gailhanou, and M. Ilegems

Appl. Phys. Lett. 71, 2331 (1997); http://dx.doi.org/10.1063/1.120022 (3 pages) | Cited 7 times

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We report evidence of a large blue shift (up to 70 meV) in the photoluminescence spectra of InAs/InP island like quantum wells following the reduction of the InP top barrier layer thickness from 6 nm to near zero. The photoluminescence intensity only starts to decrease when the top barrier thickness falls below 1.5 nm, indicating that radiative recombinations in the islands are very efficient. These results are well understood by a model assuming a vacuum confinement energy close to 5 eV. © 1997 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors

Low noise p-π-n GaN ultraviolet photodetectors

A. Osinsky, S. Gangopadhyay, R. Gaska, B. Williams, M. A. Khan, D. Kuksenkov, and H. Temkin

Appl. Phys. Lett. 71, 2334 (1997); http://dx.doi.org/10.1063/1.120023 (3 pages) | Cited 105 times

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We report on the fabrication and characterization of p-π-n GaN ultraviolet detectors. The peak responsivity at ∼ 363 nm is measured to be 0.1 A/W in the photovoltaic mode, and 0.14 A/W with a bias of −15 V. Speed measurements have shown the photoresponse to be RC-limited with the response time decreasing from 17.4 ns at zero bias to 10.3 ns at −6 V bias. For a 200×200μ m2 device, we measure the dark current to be 2.7 pA at −3 V bias, and a noise density of less than 10−25 A2/Hz, the noise floor of the measurement. Extrapolating the noise data taken at higher reverse biases, we estimate the noise equivalent power to be 6.6×10−15 W/Hz1/2. © 1997 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
42.79.Pw Imaging detectors and sensors
81.05.Ea III-V semiconductors
85.30.De Semiconductor-device characterization, design, and modeling
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Field emission properties of diamond films of different qualities

N. A. Fox, W. N. Wang, T. J. Davis, J. W. Steeds, and P. W. May

Appl. Phys. Lett. 71, 2337 (1997); http://dx.doi.org/10.1063/1.120024 (3 pages) | Cited 30 times

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Field emission properties of diamond films were studied by macroscopic I–V measurement. A lower turn-on field and a higher emission current were observed for diamond films produced by higher methane concentration, or with higher density of defects, introduced by ion implantation. However, diamond films of poorer quality experience a severe reliability problem. Cold implantation followed by rapid thermal or laser annealing produced diamond emitters with a turn-on field as low as 5 V/μm and the desired reliability. © 1997 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
61.72.up Other materials
61.72.Cc Kinetics of defect formation and annealing
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Formation of carbon-induced germanium dots

O. G. Schmidt, C. Lange, K. Eberl, O. Kienzle, and F. Ernst

Appl. Phys. Lett. 71, 2340 (1997); http://dx.doi.org/10.1063/1.120072 (3 pages) | Cited 91 times

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A very small amount of pre-deposited C on a Si substrate causes island formation after epitaxial growth of less than 2 monolayers Ge. These C-induced Ge dots can be as small as 10 nm in lateral size and 1 nm in height. Their areal density is 1011 cm−2. Intense photoluminescence signal from these small Ge quantum dots is observed reaching a maximum for 2.1±0.3 monolayers of Ge. In the initial stages of island formation, the optical transition of the wetting layer is blue-shifted by strain compensation effects. We propose spatially indirect mechanisms of radiative recombination between electrons confined in the underlying wetting layer and holes confined in the Ge islands. © 1997 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Nq Composition and phase identification
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.55.Ap Elemental semiconductors
81.05.Cy Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

A microfabricated tip for simultaneous acquisition of sample topography and high-frequency magnetic field

V. Agrawal, P. Neuzil, and D. W. van der Weide

Appl. Phys. Lett. 71, 2343 (1997); http://dx.doi.org/10.1063/1.120073 (3 pages) | Cited 8 times

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We report a combined μm-level topography and high-frequency magnetic field probe, a 6 μm loop defined on a scanning-force microscope cantilever. Since it functions as a near-zone antenna, it can be used with any suitable detector, and can probe both active and passive samples. We demonstrate its performance by scanning a coplanar waveguide sample at 10 GHz using a microwave network analyzer. With this instrument, the device noise at this frequency is ∼ 2μΦ0/Hz1/2 at T = 300 K, comparable to that found for a superconducting quantum interference device (SQUID) at DC. Unlike the SQUID, however, the thermally limited minimum-detectable field of this system scales with frequency. © 1997 American Institute of Physics.
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07.10.Cm Micromechanical devices and systems
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
07.55.Ge Magnetometers for magnetic field measurements
07.79.Lh Atomic force microscopes
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
68.35.B- Structure of clean surfaces (and surface reconstruction)
07.79.Pk Magnetic force microscopes
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
84.40.Az Waveguides, transmission lines, striplines

Spatially resolved cathodoluminescence spectra of InGaN quantum wells

Shigefusa Chichibu, Kazumi Wada, and Shuji Nakamura

Appl. Phys. Lett. 71, 2346 (1997); http://dx.doi.org/10.1063/1.120025 (3 pages) | Cited 176 times

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Spatially resolved cathodoluminescence (CL) spectrum mapping revealed a strong exciton localization in InGaN single-quantum-wells (SQWs). Transmission electron micrographs exhibited a well-organized SQW structure having abrupt InGaN/GaN heterointerfaces. However, comparison between atomic force microscopy images for GaN-capped and uncapped SQWs indicated areas of InN-rich material, which are about 20 nm in lateral size. The CL images taken at the higher and lower energy side of the spatially integrated CL peak consisted of emissions from complementary real spaces, and the area was smaller than 60 nm in lateral size. © 1997 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
81.05.Ea III-V semiconductors
72.80.Ey III-V and II-VI semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
68.35.B- Structure of clean surfaces (and surface reconstruction)

Interstitial copper-related center in n-type silicon

A. A. Istratov, H. Hieslmair, C. Flink, T. Heiser, and E. R. Weber

Appl. Phys. Lett. 71, 2349 (1997); http://dx.doi.org/10.1063/1.120026 (3 pages) | Cited 21 times

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n-type silicon samples were measured by deep level transient spectroscopy (DLTS) immediately (within one hour of storage at room temperature, required for the preparation of Schottky-diodes) after copper diffusion and quench. A donor level at Ec-(0.15±0.01) eV with a concentration of up to 1013 cm−3 was detected. The amplitude of the DLTS peak decreased with the time of storage at room temperature, and stabilized at a concentration (4 to 7)×1011 cm−3 after 15–20 h. The activation energies and prefactors of the decay of the DLTS peak in n-type Si and the reactivation of copper-compensated boron in p-type Si concur. This correlation suggests that the deep level is interstitial copper itself or a complex of interstitial copper. © 1997 American Institute of Physics.
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71.55.Cn Elemental semiconductors
66.30.J- Diffusion of impurities
61.72.J- Point defects and defect clusters

Electric-field-independent band gap superpositioning at 1.3 μm in an InGaAs–InAlAs strained-layer superlattice

I. J. Fritz, M. J. Hafich, and S. A. Casalnuovo

Appl. Phys. Lett. 71, 2352 (1997); http://dx.doi.org/10.1063/1.120027 (3 pages) | Cited 1 time

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We report on the electric-field dependent band-gap energy and near-gap absorption coefficient of a specially designed strained-layer superlattice (SLS) employing tensile strained quantum wells and having a band-gap wavelength near 1.3 μm. The SLS was grown by molecular-beam epitaxy on an InP substrate and consists of In0.43Ga0.57As wells (4.5-nm-thick) and In0.6Al0.4As barriers (6.75-nm-thick). For applied fields from zero up to at least 2.5×105 V/cm, the band-edge absorption exhibits a single peak, which we attribute to a field-independent superpositioning of the heavy- and light-hole ground states. This result agrees with tunneling resonance calculations, which predict these hole states to have the same zero-field energy and to undergo nearly identical Stark shifts. Absorption–coefficient changes of up to 104 cm−1 were readily achieved with applied biases under 15 V, suggesting potential applications to optical modulator devices. © 1997 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.20.Jq Electro-optical effects

Real time observation of surface kinetics during the self-assembly of Ga chains on Si(112)

O. J. Glembocki and S. M. Prokes

Appl. Phys. Lett. 71, 2355 (1997); http://dx.doi.org/10.1063/1.120428 (3 pages) | Cited 10 times

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Single wavelength reflectance difference anisotropy (RDA) has been used to study the kinetics of the self-assembly of Ga atom chains on faceted Si(112) surfaces. The formation of the chains is followed from the initial deposition through changes in the surface reconstruction from (5×1) to (6×1). We present a simple Monte Carlo model to account for the time evolution of the RDA signal as a function of temperature and experimentally determined kinetic parameters. © 1997 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
61.46.-w Structure of nanoscale materials
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics

X-ray photoelectron spectroscopy studies on Pd doped SnO2 liquid petroleum gas sensor

A. R. Phani

Appl. Phys. Lett. 71, 2358 (1997); http://dx.doi.org/10.1063/1.120557 (3 pages) | Cited 19 times

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The present investigation deals with the electrical response of palladium doped tin oxide, as a means of improving the selectivity for liquid petroleum gas (LPG) in the presence of CO, CH4. The sensor element with the composition of Pd(1.5 wt %) in the base material SnO2 sintered at 800 °C, has shown a high sensitivity towards LPG with a negligible cross interference of CO and CH4at an operating temperature of 350 °C. This greatly suggests the possibility of utilizing the sensor for the detection of LPG. X-ray photoelectron spectroscopy studies have been carried out to determine the possible chemical species involved in the gas-solid interaction and the enhancing mechanism of the Pd doped SnO2 sensor element, towards LPG sensitivity. © 1997 American Institute of Physics.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Antenna-coupled bolometer with a micromachined-beam thermal link

D. P. Osterman, R. Patt, R. Hunt, and J. B. Peterson

Appl. Phys. Lett. 71, 2361 (1997); http://dx.doi.org/10.1063/1.120028 (3 pages) | Cited 7 times

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We present the design of a novel bolometer intended for measurement of radiation within a waveguide. The thermal link in the bolometer is a low-thermal conductance micromachined beam. Power is coupled from an antenna to a resistive termination at the center of the beam. The optimization of the design for an astronomical measurement leads to an operating temperature of 0.48 K, accessible with a He3 refrigerator. Measurements on the antenna absorber in a waveguide show an average absorption of 94% from 33 to 50 GHz. © 1997 American Institute of Physics.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
84.40.Ba Antennas: theory, components and accessories
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment

Control of magnetic flux in a YBa2Cu3O7−δ thin film loop using femtosecond laser pulses

Masayoshi Tonouchi, Noboru Wada, Masanori Hangyo, Masahiko Tani, and Kiyomi Sakai

Appl. Phys. Lett. 71, 2364 (1997); http://dx.doi.org/10.1063/1.120029 (3 pages) | Cited 12 times

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A superconducting optical flux-trap memory with a femtosecond pulsed laser is proposed and then demonstrated. The magnetic flux is trapped in a simple YBa2Cu3O7−δ thin film loop with a polarity controlled by means of optical supercurrent modulation. After removing the external bias current, the trapped fluxes are detected by observing electromagnetic pulse radiation 60 cm away from the sample, which is excited by modulating a persistent current that circulates in the loop. The mechanism for the readin of the magnetic fluxes is discussed in relation to the current distribution in the memory. © 1997 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)

Intergranular transport properties in c-axis oriented YBa2Cu3Oy polycrystalline films

H. Ishii, S. Shingo, S. Harada, S. Hirano, Y. Iwata, T. Hara, N. Yoshida, K. Fujino, and K. Sato

Appl. Phys. Lett. 71, 2367 (1997); http://dx.doi.org/10.1063/1.120430 (3 pages)

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The current–voltage (I–V) characteristics and the resistive transition under magnetic field were extensively investigated on c-axis oriented YBCO polycrystalline films with a different amount of an in-plane grain alignment. All the parameters deduced from the scaling analyses in the intergranular region along with the vortex-glass-to-liquid transition indicate that the intergranular current transport is not via weak links but is due to strongly coupled channels regardless of a degree of an in-plane grain alignment. © 1997 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
74.25.F- Transport properties
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Sv Critical currents

Significantly enhanced flux pinning in the Bi-substituted TlBa2Ca2Cu3Oy system

V. Badri, Y. T. Wang, and A. M. Hermann

Appl. Phys. Lett. 71, 2370 (1997); http://dx.doi.org/10.1063/1.120030 (3 pages)

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We have found that substitution of bismuth into the TlBa2Ca2Cu3O9 system leads to a high temperature superconductor with significantly greater low temperature flux pinning than that of the other copper oxide superconductors. Bi substitutes at the Tl site up to 20 at. %. The superconducting transition temperature Tc increases from 110 K for x = 0.0 to 116 K for x = 0.2. Scanning electron microscope (SEM) images reveal a platelike morphology which is highly suitable for powder-in-tube processing. The magnetization–hysteresis loop shows that the Bi-substituted phase has significantly better low temperature flux pinning properties than the pristine Tl cuprate, and exhibits only a weak dependence on temperature and field when compared to that of unsubstituted phase. However, at 77 K the compound has lower Jc, determined magnetically, compared to that of the (Tl,Pb,Bi)Sr1.6Ba0.4Ca2Cu3Oy and Y-123 systems. The enhancement of superconducting properties is attributed to an increased coupling between the CuO2 planes along the c axis. Substitution of 20% of Bi in TlBa2Ca2Cu3O9 makes the compound an excellent choice for magnet wire applications at relatively low temperatures. © 1997 American Institute of Physics.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.72.-h Cuprate superconductors
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.25.Sv Critical currents
74.10.+v Occurrence, potential candidates
74.62.Dh Effects of crystal defects, doping and substitution

An ion-beam-assisted process for high-Tc Josephson junctions

M. Q. Huang, L. Chen, Z. X. Zhao, T. Yang, J. C. Nie, P. J. Wu, and X. M. Xiong

Appl. Phys. Lett. 71, 2373 (1997); http://dx.doi.org/10.1063/1.120031 (3 pages)

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We have developed a non-ion-etching ion-beam-assisted-deposition (IBAD) process for fabricating high critical-temperature (Tc) grain boundary Josephson junctions through a photoresist liftoff mask. The YBa2Cu3O7 (YBCO) junctions fabricated through this process exhibited the resistively-shunted-junction (RSJ)-like I–V characteristics. The well-defined Shapiro steps have been seen on the I–V curves under microwave radiation. The magnetic modulation of critical current of a 4 μm width YBCO junction tallied with the prior simulated Fraunhofer diffraction pattern of a Josephson junction with a spatially homogeneous critical current density. The maximum peak-to-peak modulation voltage across the dc superconducting quantum interference device (SQUID) fabricated by using these junctions reached up to 32 μV at 77 K. The magnetic modulation of the SQUID exhibited periodic behavior with the observed modulation period of 5.0×10−4 G. © 1997 American Institute of Physics.
Show PACS
74.50.+r Tunneling phenomena; Josephson effects
85.25.Cp Josephson devices
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.25.Sv Critical currents
85.25.Dq Superconducting quantum interference devices (SQUIDs)
61.72.Mm Grain and twin boundaries
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
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