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11 Feb 1991

Volume 58, Issue 6, pp. 551-658

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Compositional disordering by solid phase regrowth

W. Xia, C. C. Han, S. A. Pappert, S. N. Hsu, Z. F. Guan, P. K. L. Yu, and S. S. Lau

Appl. Phys. Lett. 58, 625 (1991); http://dx.doi.org/10.1063/1.104549 (3 pages) | Cited 5 times

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The principle of solid phase regrowth (SPR)has been used to induce compositional disordering in AlGaAs/GaAs superlattice structures in the temperature range of 400 °C (30 min)–650 °C (30 s) as compared to the conventional diffusion method in the temperature range of 600–850 °C for hours. The SPR process is simple to implement, requiring only thin‐film deposition and annealing. The crystal quality as well as the photoluminescence signals emerging from the disordered region generally improve with increasing processing temperature. The simplicity, the low process temperature, and the short process duration of the SPR technique are distinct advantages for optoelectronic applications, especially for self‐aligned devices.
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68.35.Rh Phase transitions and critical phenomena
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors
78.55.Cr III-V semiconductors
81.15.Np Solid phase epitaxy; growth from solid phases

Photoluminescence measurements for GaAs grown on Si(100) and Si(111) by molecular beam epitaxy

Z. Sobiesierski, D. A. Woolf, D. I. Westwood, and R. H. Williams

Appl. Phys. Lett. 58, 628 (1991); http://dx.doi.org/10.1063/1.104550 (3 pages) | Cited 5 times

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Photoluminescence measurements have been used to characterize Si‐doped GaAs layers, ranging in thickness from 1.1–8.1 μm, grown on Si(111) and misorientated Si(100) substrates by molecular beam epitaxy. 4.2 K PL spectra for GaAs/Si (100) show a strain‐induced splitting between the heavy and light hole valence bands which corresponds to a biaxial tensile stress of 2.8± 0.15 kbar acting on the GaAs layer. Similar measurements for GaAs/Si(111) indicate that the GaAs layer is subject to a biaxial tensile stress of 3.9±0.15 kbar at 4.2 K. Furthermore, the intensity and line shape of luminescence features for GaAs/Si(111) for the first time indicate a crystalline quality comparable with the best GaAs/Si(100) material.
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78.55.Cr III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.Gy Mechanical properties; surface strains

Photoluminescence of GaAs quantum wells grown by molecular beam epitaxy with growth interruptions

R. F. Kopf, E. F. Schubert, T. D. Harris, and R. S. Becker

Appl. Phys. Lett. 58, 631 (1991); http://dx.doi.org/10.1063/1.104551 (3 pages) | Cited 64 times

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Single GaAs/AlxGa1−xAs quantum wells, grown by molecular beam epitaxy with growth interruptions at each interface, are investigated using low‐temperature photoluminescence. The three clearly resolved photoluminescence peaks are attributed to discrete monolayer thicknesses of the well. The splitting of the peaks is investigated for several hundred points across a 2 in. wafer. The negligible variation of the peak splitting is consistent with abrupt interfaces in the growth direction, atomically smooth interfaces, and discrete thicknesses of the quantum well with changes of only integer multiples of monolayers.
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78.55.Cr III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Properties of all YBa2Cu3O7 Josephson edge junctions prepared by in situ laser ablation deposition

G. Koren, E. Aharoni, E. Polturak, and D. Cohen

Appl. Phys. Lett. 58, 634 (1991); http://dx.doi.org/10.1063/1.104552 (3 pages) | Cited 19 times

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Thin‐film YBa2Cu3O7‐YBa2Cu3O7 edge junctions of 0.4×10 μm2 cross section were prepared in situ by a multistep laser ablation deposition process. The fabrication time was about 3 h and the yield of good devices was 50%. Typical junctions reached zero resistance at 72 K and had a critical current density Jc of 300 A/cm2 at 70 K. Their Jc as a function of temperature increased slowly with decreasing temperature down to 65 K and much faster below it. In the region of low Jc we observed suppression of the critical current by a magnetic field. Under microwave radiation clear Shapiro steps were observed whose magnitude versus the microwave field agreed qualitatively with the resistively shunted junction model of a current biased junction.
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74.50.+r Tunneling phenomena; Josephson effects
74.78.-w Superconducting films and low-dimensional structures
85.25.Cp Josephson devices

Effect of Ca2PbO4 additions on the formation of the 110 K phase in Bi‐Pb‐Sr‐Ca‐Cu‐O superconducting ceramics

F. H. Chen, H. S. Koo, and T. Y. Tseng

Appl. Phys. Lett. 58, 637 (1991); http://dx.doi.org/10.1063/1.104553 (3 pages) | Cited 23 times

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The growth of the Bi2Sr2Ca2Cu3Ox phase in the high Tc superconducting Bi‐Pb‐Sr‐Ca‐Cu‐O system through reacting Bi2Sr2CaCu2Ox with Ca‐ or Cu‐rich intermediate phases, Ca2CuO3, CuO, and Ca2PbO4, has been studied. X‐ray diffraction and electrical and diamagnetic analyses revealed that the interaction and interdiffusion of these intermediate phase led to the formation of a high percentage of the 2223 phase and a sharp single‐step superconducting transition at Tc(R = 0) = 108 K. Also, Ca2PbO4 proved essential for accelerating the growth rate of the 110 K phase from the 85 K phase.
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74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
64.70.K- Solid-solid transitions
68.35.Rh Phase transitions and critical phenomena
74.70.-b Superconducting materials other than cuprates

Characteristics of interfaces for sputter deposited Bi2Sr2Ca1Cu2Ox/Bi2Sr2Cu1Oy/Bi2Sr2Ca1Cu2Oz structure

K. Mizuno, H. Higashino, K. Setsune, and K. Wasa

Appl. Phys. Lett. 58, 640 (1991); http://dx.doi.org/10.1063/1.104554 (3 pages) | Cited 4 times

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A depth profile of an Auger electron spectroscopy (AES) for a Bi2Sr2Ca1Cu2Ox/Bi2Sr2Cu1Oy/Bi2Sr2Ca1Cu2Oz structure was investigated. This multilayered structure was fabricated by an in situ sputtering process and used for sandwich‐type Josephson junctions. A little diffusion of Ca atoms from a top layer into the Bi2Sr2Cu1Oy layer was observed. It was confirmed that selective sputter etching during the AES measurement did not occur so seriously. The transition width at the two interfaces was estimated as about 10 nm, which was close to the depth resolution of our AES measurement. In addition, the interdiffusion between a Bi‐based oxide film and a MgO substrate was hardly observed.
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74.50.+r Tunneling phenomena; Josephson effects
74.78.-w Superconducting films and low-dimensional structures
85.25.Cp Josephson devices

IcR products of tunnel junctions with depressed order parameter

J. Mannhart and P. Martinoli

Appl. Phys. Lett. 58, 643 (1991); http://dx.doi.org/10.1063/1.104555 (2 pages) | Cited 15 times

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IcRN products of tunnel junctions with depressed order parameters are calculated. It is shown that in contrast to abrupt, classical tunnel junctions, IcRN products of junctions with depressed order parameter are a function of Ic with IcRN(Ic) ≤ πΔ0/2e.
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85.25.Cp Josephson devices
74.20.Fg BCS theory and its development
74.50.+r Tunneling phenomena; Josephson effects
74.25.Sv Critical currents

Cross‐sectional transmission electron microscopy observation of Nb/AlOx‐Al/Nb Josephson junctions

Takeshi Imamura and Shinya Hasuo

Appl. Phys. Lett. 58, 645 (1991); http://dx.doi.org/10.1063/1.104556 (3 pages) | Cited 13 times

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A study of microstructure of Nb/AlOx‐Al/Nb Josephson junctions by cross‐sectional transmission electron microscopy yielded much information regarding the junction barrier region. Both thick Nb and several‐nanometer Al form polycrystalline films with columnar structures. Nb is oriented to the (110) plane, and Al is (111). The 200 nm lower Nb has a wavy surface with ∼5 nm smoothness, but its surface is planarized by several nanometers Al deposited on it. Thus AlOx with a smoothness under 1 nm can be formed on Al. The upper Nb has a good crystalline structure even just above the AlOx barrier.
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74.50.+r Tunneling phenomena; Josephson effects
73.40.Rw Metal-insulator-metal structures
85.25.Cp Josephson devices

High critical current densities in YBa2Cu3O7−x thin films formed by metalorganic chemical vapor deposition at 730 °C

Y. Q. Li, J. Zhao, C. S. Chern, W. Huang, G. A. Kulesha, P. Lu, B. Gallois, P. Norris, B. Kear, and F. Cosandey

Appl. Phys. Lett. 58, 648 (1991); http://dx.doi.org/10.1063/1.104557 (3 pages) | Cited 28 times

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YBa2Cu3O7−x superconducting thin films with a critical current density of 2.3×106 A/cm2 at 77.7 K and 0 T were prepared by a metalorganic chemical vapor deposition process. The films were formed in situ on LaAlO3 at a substrate temperature of 730 °C in 2 Torr partial pressure of N2O. Resistivity and magnetic susceptibility measurements of the as‐deposited films show a sharp superconducting transition temperature of 89 K with a narrow width of less than 1 K. Critical current densities were measured by the dc transport method with a patterned bridge of 120 μm×40 μm. Both x‐ray diffraction and high‐resolution electron microscopy measurements indicate that films grew epitaxially with the c axis perpendicular to the surface of the substrate.
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74.78.-w Superconducting films and low-dimensional structures
74.25.Sv Critical currents
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Enhanced critical current density in Ca‐doped Y1Ba2Cu4O8

P. K. Narwankar, M. R. Chandrachood, D. E. Morris, and A. P. B. Sinha

Appl. Phys. Lett. 58, 651 (1991); http://dx.doi.org/10.1063/1.104558 (3 pages) | Cited 3 times

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The Jc of Ca0.1Y0.9Ba2Cu4O8 (Ca‐1:2:4) synthesized in elevated oxygen pressure is found to be ≳106 A/cm2 at low temperatures and fields, two orders of magnitude greater than the Jc of undoped Y1Ba2Cu4O8 (1:2:4). The Jc (determined by magnetic hysteresis measurements) remains high (5×105 A/cm2) up to B=4 T at 5 K, and is still ≳104 A/cm2 at 40 K and 4 T indicating strong flux pinning. At 77 K, Jc drops to 103 A/cm2 at B=1 T. Ca‐1:2:4 was partially converted to 1:2:3+CuO by brief thermal treatment to generate additional flux pinning centers, but Jc did not improve further.
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74.25.Sv Critical currents
74.70.-b Superconducting materials other than cuprates
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)

Sequential deposition growth of Bi‐Sr‐Ca‐Cu‐O systems observed using in situ reflection high‐energy electron diffraction

I. Yoshida, M. Kamei, K. Suzuki, T. Morishita, and S. Tanaka

Appl. Phys. Lett. 58, 654 (1991); http://dx.doi.org/10.1063/1.104559 (2 pages) | Cited 3 times

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The crystal growth mechanism in Bi‐Sr‐Ca‐Cu‐O thin films has been revealed by sequential deposition with an electron cyclotron resonance (ECR) oxygen plasma using in situ reflection high‐energy electron diffraction (RHEED) observation. A series of RHEED patterns presents clear evidence that the unit cell of the Bi‐Sr‐Ca‐Cu‐O structure is completed as the Bi layers have sandwiched Sr, Ca, and Cu layers. This crystalline process is not an atomic layer by atomic layer growth but a ‘‘unit cell by unit cell’’ growth.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.10.Bk Growth from vapor
74.78.-w Superconducting films and low-dimensional structures
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)

Critical heat transfer analysis of pulsed laser melting of pure metals

Biswajit Basu

Appl. Phys. Lett. 58, 656 (1991); http://dx.doi.org/10.1063/1.104560 (3 pages) | Cited 4 times

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Laser surface melting allows selective and rapid melting and solidification which leads to various improved properties. In this letter heat transfer during pulsed laser melting is critically analyzed for aluminum and iron using a numerical model. Using a pulse of few milliseconds and 0.5 mm spot radius, we show that there is a critical range of peak powers for which complete solidification occurs even before the end of the pulse. This is due to the rate of heat diffusion through the substrate being higher than the decaying laser heat flux. In this range, a directional growth of the solidification front can be expected.
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44.10.+i Heat conduction
79.20.Ds Laser-beam impact phenomena
81.40.Gh Other heat and thermomechanical treatments
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