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18 Feb 1991

Volume 58, Issue 7, pp. 663-780

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Temperature effects for current transport in resonant tunneling structures

G. D. Shen, D. X. Xu, M. Willander, G. V. Hansson, and Y. M. Wang

Appl. Phys. Lett. 58, 738 (1991); http://dx.doi.org/10.1063/1.104532 (3 pages) | Cited 5 times

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Temperature effects on current transport and the negative differential resistance for SiGe/Si and GaAlAs/GaAs resonant tunneling structures (RTS) have been studied, and the maximum working temperature Tm has been estimated. The calculations show that decreases in the carrier effective mass, well width and barrier thicknesses, lead to better temperature characteristics, implying higher peak current and larger peak‐to‐valley ratio (PVR) at higher temperature. These results are consistent with our experiment on SiGe/Si RTSs and other published experiments. The crucial role of nonresonant tunneling current Jnon in temperature effects for current transport is emphasized. Suggestions for optimizing RTS design to increase its Tm and PVR are discussed.
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73.40.Gk Tunneling
73.40.Ty Semiconductor-insulator-semiconductor structures
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Bonding configuration and defects in amorphous SiNx:H films

S. Hasegawa, M. Matsuda, and Y. Kurata

Appl. Phys. Lett. 58, 741 (1991); http://dx.doi.org/10.1063/1.104533 (3 pages) | Cited 38 times

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Amorphous SiNx:H films were prepared by rf glow discharge of SiH4‐NH3 mixtures at 300 °C, and the optical properties and the density Ns of Si dangling bonds obtained from electron spin resonance were investigated as a function of the N content x. The slope E0 in the Urbach form of the absorption coefficient and Ns, respectively, have a maximum at x=1.2 and 0.7. The dependence of E0 on x was examined on the basis of the random‐bonding model including H atoms, and the dependence of Ns was connected with the optical gap and E0, according to the weak‐bond dangling‐bond conversion model.
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78.30.Hv Other nonmetallic inorganics
78.40.Ha Other nonmetallic inorganics
61.72.S- Impurities in crystals
71.55.Ht Other nonmetals

Band offset of GaAs/In0.48Ga0.52P measured under hydrostatic pressure

Jianhui Chen, J. R. Sites, I. L. Spain, M. J. Hafich, and G. Y. Robinson

Appl. Phys. Lett. 58, 744 (1991); http://dx.doi.org/10.1063/1.104534 (3 pages) | Cited 57 times

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Low‐temperature photoluminescence spectra of an In0.48Ga0.52P alloy and a p‐type GaAs/In0.48Ga0.52P multiple quantum well, both grown by molecular beam epitaxy, have been obtained under hydrostatic pressures from 0 to 6 GPa. The zero‐pressure extrapolation of the InGaP(X) to GaAs(Γ) transitions yields a 0.40±0.02 valence‐band offset, and hence only a small, 0.06 ± 0.02 eV, conduction‐band offset. These offset values are in agreement with measured values of the confinement energy versus well width.
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62.50.-p High-pressure effects in solids and liquids
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.55.Cr III-V semiconductors

Resonant tunneling in submicron double‐barrier heterostructures

Bo Su, V. J. Goldman, M. Santos, and M. Shayegan

Appl. Phys. Lett. 58, 747 (1991); http://dx.doi.org/10.1063/1.104535 (3 pages) | Cited 48 times

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We have fabricated submicron resonant tunneling devices from double‐barrier AlGaAs/GaAs heterostructures using electron beam lithography and wet chemical etching. These devices exhibit step‐like features in the current‐voltage curves. We interpret these steps as arising from additional size quantization of the electronic states in the well due to in‐plane lithographic confinement. Magnetotunneling experiments on these devices are reported for the first time. A simple model calculation describes well the experimental data.
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73.40.Gk Tunneling
73.40.Ty Semiconductor-insulator-semiconductor structures
71.23.An Theories and models; localized states

Annealing stability in superconducting Nb wiring with nitrogen plasma treatment

Tetsuyoshi Shiota, Takeshi Imamura, and Shinya Hasuo

Appl. Phys. Lett. 58, 750 (1991); http://dx.doi.org/10.1063/1.104536 (3 pages) | Cited 4 times

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We improved the annealing stability in superconducting Nb wiring used in Josephson circuits. Nb film was exposed to nitrogen plasma just after sputtering. We measured the critical current of the Nb wiring before and after annealing. Even before annealing, the critical current with nitrogen plasma treatment is 50% higher than that without treatment. The decrease in critical current after annealing is markedly suppressed. We confirmed using secondary‐ion mass spectroscopy profiles that very little oxygen diffuses into Nb films treated using the nitrogen plasma.
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85.25.Qc Superconducting surface acoustic wave devices and other superconducting devices
74.25.Sv Critical currents

Novel all‐high Tc epitaxial Josephson junction

D. K. Chin and T. Van Duzer

Appl. Phys. Lett. 58, 753 (1991); http://dx.doi.org/10.1063/1.104537 (3 pages) | Cited 42 times

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Josephson junctions are essential components in high‐temperature superconductive integrated circuits. YBaCuO/Nb‐doped SrTiO3/YBaCuO epitaxial Josephson junctions have been designed, fabricated, and tested. The YBaCuO and Nb‐doped SrTiO3 films were deposited by off‐axis sputtering. Both dc and ac Josephson effects have been observed and the supercurrent persists up to 80 K. The critical current density is an exponential function of the barrier layer thickness. The product of critical current and normal resistance is between one and three millivolts. A superconducting quantum interference device made of the junctions displays magnetic field modulation of critical current.
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74.50.+r Tunneling phenomena; Josephson effects
74.25.N- Response to electromagnetic fields
74.78.-w Superconducting films and low-dimensional structures
85.25.Dq Superconducting quantum interference devices (SQUIDs)

Anomalous compositional dependence in in situ growth of YBaCuO films at low oxygen pressure

K. Shinohara, V. Matijasevic, P. A. Rosenthal, A. F. Marshall, R. H. Hammond, and M. R. Beasley

Appl. Phys. Lett. 58, 756 (1991); http://dx.doi.org/10.1063/1.104538 (3 pages) | Cited 8 times

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The roles of composition and oxygen pressure in in situ growth of superconducting YBaCuO films have been studied. Anomalous results are observed at low oxygen pressure. Off‐stoichiometric, Ba‐deficient films have superior superconducting properties and more bulk‐like crystal structure compared to films made on the 1:2:3 stoichiometry. Films made at low pressure have an expanded c axis compared to the bulk value, although their Tc’s are only slightly depressed. Tc and c‐axis lattice parameters are reported as a function of the deposition conditions.
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74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Electromigration failure in YBa2Cu3O7−x thin films

Satish Vitta, M. A. Stan, J. D. Warner, and S. A. Alterovitz

Appl. Phys. Lett. 58, 759 (1991); http://dx.doi.org/10.1063/1.104539 (3 pages) | Cited 6 times

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Electromigration failure in highly oriented YBa2Cu3O7−x thin films below the superconducting transition temperature is reported here for the first time. The film on SrTiO3 failed at 86 K, 2.3×105 A cm−2; while that on LaAlO3 failed at 84 K, 9.3×105 A cm−2. Scanning electron microscopy and energy dispersive x‐ray analysis of the films after failure shows that Cu migrates preferentially away from the failure region towards the electrode.
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82.45.-h Electrochemistry and electrophoresis
74.78.-w Superconducting films and low-dimensional structures
73.50.-h Electronic transport phenomena in thin films
68.35.Fx Diffusion; interface formation

In situ growth of PbSrYCaCuO films by laser ablation

R. A. Hughes, Y. Lu, T. Timusk, and J. S. Preston

Appl. Phys. Lett. 58, 762 (1991); http://dx.doi.org/10.1063/1.104540 (3 pages) | Cited 9 times

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We report the successful preparation of 1212 PbSrYCaCuO thin films by laser ablation. The films are grown in situ on (100)LaAlO3 at the relatively low substrate temperature of 610 °C. The starting composition of the target is not that of the superconductor produced. Its composition was choosen to yield the 2213 PbSrYCaCuO phase, but the structural analysis shows a predominantly 1212 film with a small impurity phase. The films are highly oriented and show superconducting transitions with onsets at 90 K and zero resistance by 75 K.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
74.78.-w Superconducting films and low-dimensional structures
74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition

Heteroepitaxial YBa2Cu3O7−x‐SrTiO3‐YBa2Cu3O7−x trilayers examined by transmission electron microscopy

Mohammed E. Tidjani, Ronald Gronsky, John J. Kingston, Frederick C. Wellstood, and John Clarke

Appl. Phys. Lett. 58, 765 (1991); http://dx.doi.org/10.1063/1.104541 (3 pages) | Cited 19 times

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We report high‐resolution transmission electron microscopy and electron diffraction studies of the heteroepitaxial superconductor‐insulator‐superconductor system YBa2Cu3O7−x‐SrTiO3‐YBa2Cu3O7−x deposited on polished (001)MgO substrates by in situ laser ablation. The resulting films grow epitaxially and consistently preserve a parallel orientation between the close‐packed (001)YBa2Cu3O7−x planes and (001)SrTiO3 planes over the entire trilayer, even in the presence of ledges or steps along vicinal interfaces. Although the interface regions showed strain occasionally relieved by stacking faults, they were free of disorder and any evidence of impurity phases. The observed epitaxial growth is very likely responsible for the excellent electrical properties found in similarly constructed multilayer interconnects.
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74.70.-b Superconducting materials other than cuprates
81.15.Np Solid phase epitaxy; growth from solid phases
68.55.-a Thin film structure and morphology
85.25.Qc Superconducting surface acoustic wave devices and other superconducting devices

Increased flux pinning in cation‐deficient Bi2(Sr,Ca)3−xCu2O8+δ

Shunji Nomura and Yet‐Ming Chiang

Appl. Phys. Lett. 58, 768 (1991); http://dx.doi.org/10.1063/1.104542 (3 pages) | Cited 5 times

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We show that flux pinning in Bi2(Sr,Ca)3−xCu2O8+δ is increased by intentional deviations in cation nonstoichiometry. Polycrystalline samples of alkaline earth‐deficient composition (x=0.24–0.32) show a larger irreversibility in magnetization (ΔM), and a slower decay of ΔM with both increasing field and time than stoichiometric compositions. The difference between compositions grows with increasing field out to 5 T, and is greatest at T≤20 K but still significant at 40 K. The critical state model yields a difference in intragranular current density (Jcm) at 20 K and 2 T of ≳102 between stoichiometric and x=0.3 compositions. Flux pinning energies determined from relaxation of magnetization are several times greater for cation‐deficient than for stoichiometric compositions. These improvements are only achieved upon slow cooling or low‐temperature annealing, indicating that defect clustering or incipient precipitation is necessary to form more effective pinning defects.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
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
74.25.Ha Magnetic properties including vortex structures and related phenomena

Atomic layer and unit cell layer growth of (Ca,Sr)CuO2 thin film by laser molecular beam epitaxy

Masaki Kanai, Tomoji Kawai, and Shichio Kawai

Appl. Phys. Lett. 58, 771 (1991); http://dx.doi.org/10.1063/1.104543 (3 pages) | Cited 68 times

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Thin films of (Ca,Sr)CuO2, the parent material of high Tc cuprate superconductors, have been formed by the laser ablation method under molecular beam epitaxial condition, and the growth mechanism has been investigated with reflection high‐energy electron diffraction (RHEED). Analyses of RHEED patterns and intensity oscillations show that this material grows with two‐dimensional layer growth. When all the metal elements are supplied simultaneously in NO2 atmosphere, the layer growth occurs with the unit‐cell layer of (Ca,Sr)CuO2. Furthermore, it has become evident that the growth unit can be separated into Ca (Sr) atomic layer and CuOx atomic layer by monitoring the RHEED intensity oscillation. The successive supply of each metal element leads to one atomic layer growth of this material.
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74.78.Fk Multilayers, superlattices, heterostructures
74.70.-b Superconducting materials other than cuprates
74.78.-w Superconducting films and low-dimensional structures
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Delay‐time measurements in narrowed waveguides as a test of tunneling

A. Ranfagni, D. Mugnai, P. Fabeni, and G. P. Pazzi

Appl. Phys. Lett. 58, 774 (1991); http://dx.doi.org/10.1063/1.104544 (3 pages) | Cited 76 times

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Delay‐time measurements with a microwave setup, where a step narrowing in the waveguide simulates a quantum mechanical potential barrier, have been performed even beyond the cutoff. This allows experimental measurements in a very accessible temporal range of the order of nanoseconds. The results, interpreted as tunneling times, are compared with the existing quantum mechanical models, translated into the electromagnetic framework.
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03.65.Sq Semiclassical theories and applications
42.50.-p Quantum optics
74.50.+r Tunneling phenomena; Josephson effects
73.40.Gk Tunneling

Cation termination at ion‐polished and chemically etched (001)YBa2Cu3O7 crystal surfaces: An ion channeling study

A. T. Fiory, A. F. Hebard, R. H. Eick, L. F. Schneemeyer, J. V. Waszczak, and H.‐J. Gossmann

Appl. Phys. Lett. 58, 777 (1991); http://dx.doi.org/10.1063/1.104515 (3 pages)

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Local cation order approaching ideal bulk termination was found for cleaned (001) surfaces of YBa2Cu3O7 crystals by ion‐channeling surface‐peak analysis. Surfaces etched in dilute CH3OH:Br2 and ultrasonically agitated in CH3OH to dislodge the Br2 appear terminated preferentially by the Cu‐O ‘‘double‐plane’’ sequence, containing less than 1/2‐cation monolayer of surface disorder. Planar polishing with ion beams incident at a glancing angle on a rotating crystal leaves residual disorder as low as ∼8 Å, damage which is readily removed by a light chemical etch.
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74.78.-w Superconducting films and low-dimensional structures
81.65.-b Surface treatments
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
FREE

Erratum: Electric field screening by photogenerated holes in multiple quantum wells: A new mechanism for absorption saturation [Appl. Phys. Lett. 57, 1081 (1990)]

Thomas H. Wood, J. Z. Pastalan, Charles A. Burrus, Bart C. Johnson, Barry I. Miller, Jose L. deMiguel, Uziel Koren, and Martin G. Young

Appl. Phys. Lett. 58, 780 (1991); http://dx.doi.org/10.1063/1.105248 (1 page)

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Abstract Unavailable
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78.20.Jq Electro-optical effects
99.10.Cd Errata
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