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20 Sep 1993

Volume 63, Issue 12, pp. 1595-1706

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Self‐consistent simulation of Stark shift of intersubband transition in modulation‐doped step quantum wells

F. Y. Huang, J. Li, Lie‐Ming Li, and H. Morkoç

Appl. Phys. Lett. 63, 1669 (1993); http://dx.doi.org/10.1063/1.110732 (3 pages) | Cited 8 times

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Self‐consistent simulations, including free carrier screening and many body effects, have been carried out for Stark shifts of intersubband transitions in step quantum wells. Unlike carrier screening in single quantum wells, where the charge distribution screens the applied field and reduces the Stark shift, our numerical results show that the asymmetric nature of the step quantum well may yield to an enhancement in the Stark shift. Discrepancies between experimental data and theoretical simulations are also addressed.
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71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.66.Fd III-V semiconductors

Low‐frequency noise behavior of γ‐irradiated partially depleted silicon‐on‐insulator n‐channel metal‐oxide‐semiconductor transistors

E. Simoen and C. Claeys

Appl. Phys. Lett. 63, 1672 (1993); http://dx.doi.org/10.1063/1.110733 (3 pages) | Cited 1 time

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This letter discusses the low‐frequency noise behavior of partially depleted silicon‐on‐insulator n‐channel metal‐oxide‐semiconductor transistors after γ irradiation to a total dose of 100 krad(Si). The noise characteristics both in linear operation and in saturation are investigated in detail. It is shown that the increase of the noise in the linear region is mainly due to the degradation of the sidewall isolation regions. In contrast, the so‐called kink‐related noise overshoot is hardly affected by the irradiation, indicating that its origin is most likely not interface related. This result will be discussed in view of a recently proposed model for the noise overshoot.  
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85.30.Tv Field effect devices
72.70.+m Noise processes and phenomena
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.80.Ed γ-ray effects

Phosphorus doping of epitaxial Si and Si1−xGex at very low pressure

Syun‐Ming Jang, Kenneth Liao, and Rafael Reif

Appl. Phys. Lett. 63, 1675 (1993); http://dx.doi.org/10.1063/1.110734 (3 pages) | Cited 11 times

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We report on the in situ P doping of Si1−xGex(SiH4/GeH4) and Si(SiH4) epitaxial films with 1–100 ppm PH3 at 620 °C in a very low pressure chemical vapor deposition reactor. The epitaxial growth rates were found to decrease with P doping. The growth rate reduction is a function of Ge composition and is less pronounced as the Ge content increases. In addition, P incorporation into the growing film is affected by Ge, which improves the concentration range and profile definition of P. A simple model that attempts to explain the results is discussed.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Interfacial alloy formation in ZnSe/CdSe quantum‐well heterostructures characterized by photoluminescence spectroscopy

Ziqiang Zhu, Hiroteru Yoshihara, Kazuhisa Takebayashi, and Takafumi Yao

Appl. Phys. Lett. 63, 1678 (1993); http://dx.doi.org/10.1063/1.110708 (3 pages) | Cited 19 times

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The interface of a binary single quantum‐well (SQW) structure of ZnSe/CdSe, where CdSe less than one monolayer is sandwiched by ZnSe layers (submonolayer SQW), is characterized by photoluminescence spectroscopy. The dependence of the energy, linewidth, and intensity of excitonic emission from submonolayer SQWs on the well thickness of CdSe is extensively investigated. The characteristics of the excitonic emission are interpreted in terms of alloy formation at the interface.
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78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
68.55.-a Thin film structure and morphology
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Superconducting Josephson arrays as tunable microwave sources operating at 77 K

J. S. Martens, A. Pance, K. Char, L. Lee, S. Whiteley, and V. M. Hietala

Appl. Phys. Lett. 63, 1681 (1993); http://dx.doi.org/10.1063/1.110709 (3 pages) | Cited 16 times

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High‐temperature superconducting arrays of Josephson junctions have been fabricated and tested as millimeter‐wave oscillators at 77 K. Power levels in the microwatt range have been detected in the range of 90–160 GHz from arrays using from 350 to almost 60 000 YBa2Cu3O7 junctions. Monolithic log‐periodic spiral antennas as well as quasioptical resonators have been used to enable power coupling. The arrays were also found to be bias tunable over ranges limited by the receiving apparatus.
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85.25.Cp Josephson devices
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.72.-h Cuprate superconductors

Critical current versus normal‐state resistivity in granular Y1Ba2Cu3O7−δ

A. Díaz, A. Pomar, G. Domarco, J. Maza, and Félix Vidal

Appl. Phys. Lett. 63, 1684 (1993); http://dx.doi.org/10.1063/1.110684 (3 pages) | Cited 7 times

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Precision measurements of critical current densities at zero applied magnetic field Jc for six granular Y1Ba2Cu3O7−δ samples have been performed by using a low frequency induction method. Also, the intergrain resistivity ρct for each sample has been extracted from the normal‐state resistivity. It is found experimentally that at any temperature distance from the transition, Jc is inversely proportional to ρct. A way to estimate Jc from the resistivity of the granular samples in the normal state is thus open.
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74.25.Sv Critical currents
74.81.Bd Granular, melt-textured, amorphous, and composite superconductors
74.72.-h Cuprate superconductors

Effect of noise and capacitance on the dynamical characteristics of high‐Tc Josephson junctions

F. Busse, R. Nebel, P. Herzog, M. Darula, and P. Seidel

Appl. Phys. Lett. 63, 1687 (1993); http://dx.doi.org/10.1063/1.110685 (3 pages) | Cited 8 times

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The dynamical characteristics of Josephson junctions at finite temperatures are simulated in the resistively shunted junction model including a capacitance and a current source producing white noise. It is shown how the height and the shape of the Shapiro steps as a function of the microwave amplitude are affected by noise as well as by the capacitance. The results of the simulations are found to be in good agreement with recently published experimental data on different types of Josephson weak links fabricated from high‐Tc materials.
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74.50.+r Tunneling phenomena; Josephson effects
85.25.Cp Josephson devices
74.81.-g Inhomogeneous superconductors and superconducting systems, including electronic inhomogeneities
74.72.-h Cuprate superconductors

High‐Tc multilayer step‐edge Josephson junctions and SQUIDs

N. Missert, T. E. Harvey, R. H. Ono, and C. D. Reintsema

Appl. Phys. Lett. 63, 1690 (1993); http://dx.doi.org/10.1063/1.110686 (3 pages) | Cited 23 times

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We have developed a reliable process to fabricate high‐quality YBa2Cu3O7−x (YBCO) superconductor‐normal metal‐superconductor (SNS) step‐edge junctions and SQUIDs over YBCO ground planes. These multilevel circuits employ thin films of SrTiO3 and NdGaO3 as the insulating layer between the active device and the ground plane and use Ag as the normal metal in the Josephson junction. The reproducibility and uniformity of the junctions are better than our single‐level devices grown directly on step edges cut into single‐crystal substrates. Here the critical current variation among junctions on a single wafer is less than a factor of 2. Junctions grown on thin‐film step edges of SrTiO3 have critical currents near 2 mA at 4 K, while those grown on NdGaO3 step edges have critical currents near 0.5 mA at 4 K.
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74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
85.25.Cp Josephson devices
85.25.Dq Superconducting quantum interference devices (SQUIDs)
74.78.-w Superconducting films and low-dimensional structures

Imaging of magnetic vortices in superconducting networks and clusters by scanning SQUID microscopy

L. N. Vu, M. S. Wistrom, and D. J. Van Harlingen

Appl. Phys. Lett. 63, 1693 (1993); http://dx.doi.org/10.1063/1.110687 (3 pages) | Cited 67 times

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We have imaged the configuration of trapped magnetic vortices in two‐dimensional superconductor arrays and clusters using a scanning SQUID microscope (SSM). The SSM scans a dc SQUID detector over the array surface, achieving better than 10 μm spatial resolution over a scan range up to 1 cm×1 cm and a magnetic flux sensitivity of about 10−4Φ0. We have obtained images of large square arrays cooled at different values of applied magnetic flux per cell Φ. For low rational values (1/2,1/3,1/4,...) of the frustration parameter f=Φ/Φ0, we find regions of periodically arranged vortices separated by domain walls; at other values of the field, the vortex pattern is disordered. We also present observations of vortex patterns in ensembles of 3×3 clusters.
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07.55.-w Magnetic instruments and components
74.25.-q Properties of superconductors

High quality YBa2Cu3O7 Josephson junctions made by direct electron beam writing

S. K. Tolpygo, S. Shokhor, B. Nadgorny, J.‐Y. Lin, M. Gurvitch, A. Bourdillon, S. Y. Hou, and Julia M. Phillips

Appl. Phys. Lett. 63, 1696 (1993); http://dx.doi.org/10.1063/1.110688 (3 pages) | Cited 25 times

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High‐Tc Josephson junctions have been fabricated by direct electron beam writing over YBa2Cu3O7 thin‐film microbridges, using scanning transmission electron microscope (STEM) with an accelerating voltage of 80–120 kV. Annealing at 330–380 K increases Tc and Ic of the junctions and makes them more stable. In the operating range of a few degrees below Tc, the junctions show 100% magnetic field modulation of the critical current, microwave‐induced Shapiro steps oscillating according to the resistively shunted junction (RSJ) model, and RSJ current‐voltage characteristics with IcRn product up to 0.5–0.6 mV at 75 K and 0.3 mV at 77 K.
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74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures

150% magnetoresistance in sputtered Fe/Cr(100) superlattices

Eric E. Fullerton, M. J. Conover, J. E. Mattson, C. H. Sowers, and S. D. Bader

Appl. Phys. Lett. 63, 1699 (1993); http://dx.doi.org/10.1063/1.110689 (3 pages) | Cited 50 times

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We report the epitaxial growth of Fe/Cr(100) superlattices onto MgO(100) single‐crystal substrates by magnetron sputtering. Superlattices that are epitaxially oriented within 1° both in‐plane and out‐of‐plane with the MgO substrate are achieved by initial growth of a Cr base layer at high temperature. Multiple superlattice diffraction peaks are observed in the low‐ and high‐angle x‐ray diffraction spectra. Three peaks are observed in the magnetoresistance associated with the oscillatory antiferromagnetic interlayer magnetic coupling as a function of Cr thickness. A maximum magnetoresistance of 150% at 4.2 K (28% at room temperature) is observed for a Cr(100 Å)/[Fe(14 Å)/Cr(8 Å)]50 superlattice.
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68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.70.-i Magnetic properties of thin films, surfaces, and interfaces

Linear magnetoresistive change at zero field in Cu/Co/Cu/NiFe multilayers

D. Miyauchi and S. Araki

Appl. Phys. Lett. 63, 1702 (1993); http://dx.doi.org/10.1063/1.110690 (3 pages) | Cited 4 times

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Cu/Co/Cu/NiFe multilayers were prepared by molecular beam epitaxy and their magnetoresistive (MR) properties in dc and ac magnetic field were studied. With a view to application such as MR head, minor loops of MR transfer curves with applied fields of ±50 Oe were particularly investigated. By optimizing the thickness of each layer, a linear and nonhysteretic MR response was obtained. The output voltage was roughly estimated as two and a half times that of a conventional NiFe element in an ac magnetic field at 50 Hz.
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75.70.-i Magnetic properties of thin films, surfaces, and interfaces
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.15.Gd Galvanomagnetic and other magnetotransport effects
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

High‐pressure conductivity of Au(dmit)2 Langmuir–Blodgett films

Yasuhiro F. Miura, Heikki Isotalo, Kenji Kawaguchi, Takayoshi Nakamura, and Mutsuyoshi Matsumoto

Appl. Phys. Lett. 63, 1705 (1993); http://dx.doi.org/10.1063/1.110691 (2 pages) | Cited 6 times

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The conductivity of the mixed Langmuir–Blodgett films of tridecylmethylammonium‐ Au(dmit)2 and icosanoic acid after electrochemical oxidation in LiClO4 aqueous solution was measured under pressure up to 14 kbar. The room‐temperature conductivity (σRT=12 S/cm) increased with an increase in pressure reaching 2.85 times larger value at 14 kbar compared to that under ambient pressure. The temperature at which the film exhibits its maximum conductivity was shifted to lower temperature upon applying pressure without pronounced saturation.
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73.61.Ph Polymers; organic compounds
68.18.-g Langmuir-Blodgett films on liquids
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