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17 Aug 1998

Volume 73, Issue 7, pp. 865-1010

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The role of zinc pre-exposure in low-defect ZnSe growth on As-stabilized GaAs (001)

S. Miwa, L. H. Kuo, K. Kimura, T. Yasuda, A. Ohtake, C. G. Jin, and T. Yao

Appl. Phys. Lett. 73, 939 (1998); http://dx.doi.org/10.1063/1.122045 (3 pages) | Cited 10 times

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Zinc coverage and the structures of Zn-exposed As-stabilized GaAs(001)-(2×4) and -c(4×4) surfaces have been studied using x-ray photoelectron spectroscopy and scanning tunneling microscopy in order to clarify the role of the Zn pre-exposure process in ZnSe growth on GaAs(001). Since Zn atoms stick on the GaAs-(2×4) surface even though their interaction is very weak, Zn may act as a balancer to form a neutral ZnSe/GaAs interface. Zn can also remove excess As atoms and make a “pure” (2×4) structure that is the only possible starting surface for low-defect ZnSe heteroexpitaxy on a GaAs(001) surface. © 1998 American Institute of Physics.
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79.60.Jv Interfaces; heterostructures; nanostructures
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Dz II-VI semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Rh Phase transitions and critical phenomena

Thermal stability of W and WSix contacts on p-GaN

X. A. Cao, S. J. Pearton, F. Ren, and J. R. Lothian

Appl. Phys. Lett. 73, 942 (1998); http://dx.doi.org/10.1063/1.122046 (3 pages) | Cited 27 times

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The annealing temperature (400–1100 °C) and measurement temperature (25–300 °C) dependencies of current–voltage characteristics of W and WSi0.45 contacts on p-GaN have been compared to the more common Ni/Au metallization. At 25 °C, slightly rectifying characteristics were obtained for all three types of contact, but at 300 °C specific contact resistances in the 10−2 Ω cm2 range were obtained for WSi0.45 and Ni/Au. This is due to an increase in Mg acceptor ionization efficiency (from 10% at 25 °C to 57% at 300 °C) and more efficient thermionic hole emission across the metal-GaN interface. Both WSi0.45 and W contacts retained featureless surface morphology for annealing at >900 °C, whereas Ni/Au showed substantial islanding at ⩽700 °C. © 1998 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
85.40.Ls Metallization, contacts, interconnects; device isolation
73.40.Cg Contact resistance, contact potential
73.61.Ey III-V semiconductors
68.60.Dv Thermal stability; thermal effects
61.72.Cc Kinetics of defect formation and annealing

Hydrogen passivation of silicon carbide by low-energy ion implantation

N. Achtziger, J. Grillenberger, W. Witthuhn, M. K. Linnarsson, M. Janson, and B. G. Svensson

Appl. Phys. Lett. 73, 945 (1998); http://dx.doi.org/10.1063/1.122047 (3 pages) | Cited 28 times

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Ion implantation of deuterium is performed to investigate the mobility and passivating effect of hydrogen in epitaxial α-SiC (polytypes 4H and 6H). To avoid excessive damage and the resulting trapping of hydrogen, the implantation is performed with low energy (600 eV 2H2+). The 2H depth profile is analyzed by secondary ion mass spectrometry. Electrical properties are measured by capacitance–voltage profiling and admittance spectroscopy. In p-type SiC, hydrogen diffuses on a μm scale even at room temperature and effectively passivates acceptors. In n-type SiC, the incorporation of H is suppressed and no passivation is detected. © 1998 American Institute of Physics.
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81.65.Rv Passivation
81.05.Hd Other semiconductors
61.72.up Other materials
66.30.J- Diffusion of impurities
61.80.Jh Ion radiation effects
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

The Meyer–Neldel rule in fullerenes

J. C. Wang and Y. F. Chen

Appl. Phys. Lett. 73, 948 (1998); http://dx.doi.org/10.1063/1.122048 (3 pages) | Cited 29 times

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We report that the thermally activated conductivity in several fullerene systems obeys the Meyer–Nelder (MN) rule, σ = σ00eΔE/kT0e−ΔE/kT. We found that the MN conductivity σ00 and the characteristic energy kT0 have a strong correlation, which is in good agreement with the prediction of the model proposed by Crandall [R. S. Crandall, Phys. Rev. B 43, 4057 (1991)] and Chen [Y. F. Chen and S. F. Huang, Phys. Rev. B 44, 13 775 (1991)]. In this model, the origin of the MN rule is attributed to the exponential energy distribution of the defect traps. A similar correlation between σ00 and kT0 is also found in chalcogenide glasses. © 1998 American Institute of Physics.
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72.80.Rj Fullerenes and related materials
71.20.Tx Fullerenes and related materials; intercalation compounds
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Dynamic self-organization of strained islands during SiGe epitaxial growth

J. A. Floro, E. Chason, M. B. Sinclair, L. B. Freund, and G. A. Lucadamo

Appl. Phys. Lett. 73, 951 (1998); http://dx.doi.org/10.1063/1.122049 (3 pages) | Cited 44 times

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Dynamic self-organization of coherently strained islands during SiGe molecular beam epitaxy on Si(001) is measured in real time using a novel spectroscopic light scattering technique. We show that an array of hut clusters self-orders on a square mesh with increasing areal coverage. Ordering occurs to minimize the repulsive elastic interactions between neighboring islands. Self-organization breaks down when islands coalesce during deposition or during static coarsening. © 1998 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.66.Li Other semiconductors
81.05.Hd Other semiconductors

Model of leakage characteristics of (Ba, Sr)TiO3 thin films

S. Maruno, T. Kuroiwa, N. Mikami, K. Sato, S. Ohmura, M. Kaida, T. Yasue, and T. Koshikawa

Appl. Phys. Lett. 73, 954 (1998); http://dx.doi.org/10.1063/1.122050 (3 pages) | Cited 49 times

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We have investigated the dependence of leakage current and capacitance of Pt/Ba0.5Sr0.5TiO3/Pt capacitors on annealing temperature under high vacuum conditions. It is observed that leakage currents increase asymmetrically for negative and positive bias voltage with increasing annealing temperature. A model of leakage current and capacitance characteristics has been proposed on the assumption of generation of oxygen vacancies by annealing at the interfaces of the dielectric film adjacent to the Pt electrodes. The model predicts the oxygen vacancies of about 1020 cm−3. © 1998 American Institute of Physics.
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77.55.-g Dielectric thin films
84.32.Tt Capacitors
81.40.Gh Other heat and thermomechanical treatments
81.40.Rs Electrical and magnetic properties related to treatment conditions
61.72.J- Point defects and defect clusters

Heteroepitaxial growth of BeSe on vicinal Si(001) surfaces

C. Chauvet, P. Venneguès, P. Brunet, E. Tournié, and J. P. Faurie

Appl. Phys. Lett. 73, 957 (1998); http://dx.doi.org/10.1063/1.122051 (3 pages) | Cited 11 times

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The growth of BeSe on vicinal Si(001) substrates has been investigated by molecular beam epitaxy. Reflection high energy electron diffraction was used to study the initial growth mode and the surface structure. Efforts have been done at the early steps of the growth in order to optimize the interface quality. Transmission electron microscopy revealed a BeSe layer relaxed with misfit dislocations and stacking faults that are mainly confined near the heterointerface. These results are promising in view of the growth of Zn0.55Be0.45Se alloy that is lattice matched to silicon. There will be many potential applications of this alloy—in the case of a direct band gap—in the frame of Si-based optoelectronic devices. © 1998 American Institute of Physics.
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81.05.Hd Other semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Nn Stacking faults and other planar or extended defects
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Thermal stability of GaN investigated by Raman scattering

M. Kuball, F. Demangeot, J. Frandon, M. A. Renucci, J. Massies, N. Grandjean, R. L. Aulombard, and O. Briot

Appl. Phys. Lett. 73, 960 (1998); http://dx.doi.org/10.1063/1.122052 (3 pages) | Cited 36 times

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We have investigated the thermal stability of GaN using Raman scattering. Noninvasive optical monitoring of structural damage to GaN by high-temperature anneals in nitrogen ambient has been demonstrated. Characteristic features in the Raman spectrum identify three thermal stability regimes. Thermal damage between 900 and 1000 °C results in the appearance of a broad Raman peak between the E2 and A1(LO) phonon. For anneals at temperatures higher than 1000 °C emerging macroscopic disorder gives rise to distinct Raman modes at 630, 656, and 770 cm−1. Below 900 °C no thermal damage has been observed. The evolution of the Raman spectrum of GaN with increasing annealing temperature is discussed in terms of disorder-induced Raman scattering. We find clear indications for a reaction at the GaN/sapphire interface for anneals higher than 1000 °C. © 1998 American Institute of Physics.
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68.60.Dv Thermal stability; thermal effects
78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
63.20.-e Phonons in crystal lattices
68.55.-a Thin film structure and morphology

Growth and characterization of InGaAs/InGaP quantum dots for midinfrared photoconductive detector

S. Kim, H. Mohseni, M. Erdtmann, E. Michel, C. Jelen, and M. Razeghi

Appl. Phys. Lett. 73, 963 (1998); http://dx.doi.org/10.1063/1.122053 (3 pages) | Cited 70 times

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We report InGaAs quantum dot intersubband infrared photodetectors grown by low-pressure metalorganic chemical vapor deposition on semi-insulating GaAs substrates. The optimum growth conditions were studied to obtain uniform InGaAs quantum dots constructed in an InGaP matrix. Normal incidence photoconductivity was observed at a peak wavelength of 5.5 μm with a high responsivity of 130 mA/W and a detectivity of 4.74×107 cm H1/2/W at 77 K. © 1998 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.-q Optoelectronic devices
72.40.+w Photoconduction and photovoltaic effects
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Vacancy ordering of Ga2Se3 at GaSe/GaAs(100) interface

Z. R. Dai and F. S. Ohuchi

Appl. Phys. Lett. 73, 966 (1998); http://dx.doi.org/10.1063/1.122054 (3 pages) | Cited 9 times

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Vacancy ordering was directly observed by high resolution transmission electron microscopy (HRTEM) at the heterointerface of GaSe/GaAs(100) grown by molecular beam epitaxy. Ga2Se3 crystalline film forms immediately to the GaAs (100) substrate, acting as an intermediate layer with thickness of 1.6–3.2 nm between the GaSe film and the GaAs substrate. Combining with fast Fourier transform analysis and simulations of HRTEM images and diffraction patterns, vacancy ordering in the Ga2Se3 was investigated. The vacancies preferably distribute on the (100) crystal planes of α-Ga2Se3 with a zinc-blende structure and the vacancy sheet appears on the planes of each three separated Ga sheets. © 1998 American Institute of Physics.
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68.35.Ct Interface structure and roughness
61.72.J- Point defects and defect clusters
68.35.Fx Diffusion; interface formation

Emission spectra and mode structure of InAs/GaAs self-organized quantum dot lasers

L. Harris, D. J. Mowbray, M. S. Skolnick, M. Hopkinson, and G. Hill

Appl. Phys. Lett. 73, 969 (1998); http://dx.doi.org/10.1063/1.122055 (3 pages) | Cited 85 times

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A study of the emission spectra and mode structure of InAs/GaAs self-organized quantum dot lasers is presented. In contrast to conventional bulk or quantum well lasers, the number of lasing modes increases above threshold. This behavior is shown to be consistent with carriers localized in noninteracting dots and a resultant inhomogeneously broadened gain spectrum. The lasing spectra are found to have a complicated form with groups of longitudinal modes separated by nonlasing spectral regions and lasing occurring via a number of different lateral modes. These characteristics are discussed in terms of the spatially discrete nature of the quantum dots. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Nonlinear electron transport characteristics in ultrathin wires of recrystallized hydrogenated amorphous silicon

V. Ng, H. Ahmed, and T. Shimada

Appl. Phys. Lett. 73, 972 (1998); http://dx.doi.org/10.1063/1.122056 (3 pages) | Cited 8 times

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Electron transport in nanowires of hydrogenated amorphous silicon recrystallized by electron beam annealing has been studied. Evidence for single electron effects with I–V characteristics at low temperature has been presented. The region of the nonlinear I–V characteristics is modeled as a hopping conduction between limited number of trapping sites in amorphous regions or at grain boundaries with Coulomb blockade effect. Transmission electron microscopy is used to support this hypothesis. © 1998 American Institute of Physics.
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73.61.Jc Amorphous semiconductors; glasses
73.61.Cw Elemental semiconductors
73.23.Hk Coulomb blockade; single-electron tunneling
61.72.Cc Kinetics of defect formation and annealing
61.80.Fe Electron and positron radiation effects
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Electrical characterization of GaN p-n junctions with and without threading dislocations

P. Kozodoy, J. P. Ibbetson, H. Marchand, P. T. Fini, S. Keller, J. S. Speck, S. P. DenBaars, and U. K. Mishra

Appl. Phys. Lett. 73, 975 (1998); http://dx.doi.org/10.1063/1.122057 (3 pages) | Cited 138 times

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The effect of dislocations on the electrical characteristics of GaN p-n junctions has been examined through current–voltage measurements. Lateral epitaxial overgrowth (LEO) was used to produce areas of low dislocation density in close proximity to areas with the high dislocation density typical for growth on sapphire. A comparison of p-n diodes fabricated in each region reveals that reverse-bias leakage current is reduced by three orders of magnitude on LEO GaN. Temperature-dependent measurements on the LEO diodes indicate that the remaining leakage current in these devices is associated with a deep trap level. © 1998 American Institute of Physics.
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85.30.Kk Junction diodes
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
71.55.Eq III-V semiconductors

High gain GaN/AlGaN heterojunction phototransistor

Wei Yang, Thomas Nohava, Subash Krishnankutty, Robert Torreano, Scott McPherson, and Holly Marsh

Appl. Phys. Lett. 73, 978 (1998); http://dx.doi.org/10.1063/1.122058 (3 pages) | Cited 13 times

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A GaN/AlGaN heterojunction bipolar phototransistor with gain in excess of 105 was demonstrated. From 360 to 400 nm, an eight orders of magnitude drop in responsivity was achieved. The phototransistor features a rapid electrical quenching of persistent photoconductivity, and exhibits high dark impedance and no dc drift. By changing the frequency of the quenching cycles, the detection speed of the phototransistor can be adjusted to accommodate specific applications. These results represent an internal gain UV detector with significantly improved performance over GaN-based photoconductors. © 1998 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Pz Photoconduction and photovoltaic effects
85.60.Dw Photodiodes; phototransistors; photoresistors
85.60.Gz Photodetectors (including infrared and CCD detectors)

Strong excitonic recombination radiation from homoepitaxial diamond thin films at room temperature

Hideyuki Watanabe, Kazushi Hayashi, Daisuke Takeuchi, Sadanori Yamanaka, Hideyo Okushi, Koji Kajimura, and Takashi Sekiguchi

Appl. Phys. Lett. 73, 981 (1998); http://dx.doi.org/10.1063/1.122059 (3 pages) | Cited 47 times

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We have observed strong emission lines at 5.27 and 5.12 eV at room temperature in cathodoluminescence spectra from homoepitaxial diamond films grown by step-flow mode prepared with microwave plasma assisted chemical vapor deposition. The temperature dependence of integrated intensity of the emission lines indicates that they are attributed to free-exciton recombination radiation associated with a transverse optical phonon and its replica. These results have demonstrated the superior crystalline quality of the homoepitaxial diamond films grown by the step-flow mode. © 1998 American Institute of Physics.
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78.60.Hk Cathodoluminescence, ionoluminescence
78.66.Db Elemental semiconductors and insulators
81.05.Cy Elemental semiconductors
81.05.ub Fullerenes and related materials
68.55.-a Thin film structure and morphology
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
63.20.kk Phonon interactions with other quasiparticles
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
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Microwave electric-field imaging using a high-Tc scanning superconducting quantum interference device

S. Chatraphorn, E. F. Fleet, R. C. Black, and F. C. Wellstood

Appl. Phys. Lett. 73, 984 (1998); http://dx.doi.org/10.1063/1.122060 (3 pages) | Cited 5 times

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We have used a 77 K thin-film YBa2Cu3O7 superconducting quantum interference device (SQUID) in a scanning SQUID microscope to image room-temperature sources of high-frequency electric field. We find that time-varying electric fields capacitively induce currents in the SQUID, which in turn are rectified by the nonlinearity of the SQUID current–voltage characteristics, leading to changes in the quasistatic voltage across the SQUID. By observing changes in the voltage modulation depth ΔV of the SQUID as a sample is scanned past the SQUID, we obtain electric-field images in the 1–15 GHz frequency range with a SQUID-to-sample separation of about 80 μm. © 1998 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
85.25.Dq Superconducting quantum interference devices (SQUIDs)
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
74.50.+r Tunneling phenomena; Josephson effects

Influence of the number of deposited atoms per shuttering cycle on surface morphology of sequentially deposited Pb2Sr2EuCu3Oy films

Yuichi Motoi and Sumio Ikegawa

Appl. Phys. Lett. 73, 987 (1998); http://dx.doi.org/10.1063/1.122061 (3 pages) | Cited 3 times

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The relation between surface morphology and growth conditions on Pb2Sr2EuCu3Oy (Pb-3212) thin films has been studied. The Pb-3212 thin films were grown by the molecular beam epitaxy method with monolayer-by-monolayer deposition. It was found that the surface morphology depends on the amounts of atoms deposited per unit area during one cycle of deposition sequence to form the Pb-3212 unit cell. The Cu2O precipitates were observed when the amount for Cu is larger than the ideal value or that for Sr is less than the ideal value. The averaged roughness of the smoothest film grown under Sr-rich and Cu-deficient conditions is less than 0.30 nm. © 1998 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)
74.72.-h Cuprate superconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology

High-performance (Hg, Re)Ba2CaCu2Oy grain-boundary Josephson junctions and dc superconducting quantum interference devices

A. Tsukamoto, K. Takagi, Y. Moriwaki, T. Sugano, S. Adachi, and K. Tanabe

Appl. Phys. Lett. 73, 990 (1998); http://dx.doi.org/10.1063/1.122062 (3 pages) | Cited 10 times

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High-performance grain-boundary Josephson junctions and dc superconducting quantum interference devices (SQUIDs) have been fabricated using c-axis oriented (Hg, Re)Ba2CaCu2Oy thin films grown on bicrystal SrTiO3 substrates with a 24° misorientation angle. The junctions exhibit supercurrent up to a temperature close to the film Tc and resistively shunted junctionlike current–voltage characteristics. A rather high IcRn product of 400–460 μV is observed at 77 K in some junctions. The dc SQUIDs show a field-induced periodic voltage up to 111 K. They also exhibit a voltage modulation depth as large as 90, 27, and 1–2 μV at 77, 97, and 111 K, respectively. © 1998 American Institute of Physics.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
85.25.Cp Josephson devices
74.50.+r Tunneling phenomena; Josephson effects
61.72.Mm Grain and twin boundaries
74.10.+v Occurrence, potential candidates
81.65.Cf Surface cleaning, etching, patterning
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

Field-dependent microsusceptometry on magnetic crystallites with integrated dc SQUIDs

L. R. Narasimhan, C. K. N. Patel, and M. B. Ketchen

Appl. Phys. Lett. 73, 993 (1998); http://dx.doi.org/10.1063/1.122063 (3 pages) | Cited 2 times

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We report the use of unshielded planar low-Tc dc SQUIDs for temperature-dependent ac and dc magnetic susceptibility measurements on small particles in magnetic fields of up to 300 G. These measurements were made with integrated microsusceptometers which can operate in such fields when applied in the plane of the device. We show paramagnetic, antiferromagnetic, and superconducting behavior on various samples of order 20–50 μm from 0.3 to 4 K and discuss the effect of sample placement on the magnitude of the signal. © 1998 American Institute of Physics.
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07.55.Jg Magnetometers for susceptibility, magnetic moment, and magnetization measurements
85.25.Hv Superconducting logic elements and memory devices; microelectronic circuits
75.50.Tt Fine-particle systems; nanocrystalline materials
85.25.Dq Superconducting quantum interference devices (SQUIDs)
75.30.Cr Saturation moments and magnetic susceptibilities

Nb/Al/AlOx/AlOx/Al/Nb Josephson junctions for programmable voltage standards

H. Schulze, R. Behr, F. Müller, and J. Niemeyer

Appl. Phys. Lett. 73, 996 (1998); http://dx.doi.org/10.1063/1.122064 (3 pages) | Cited 60 times

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We present a study of the microwave characteristics of Josephson junctions based on a superconductor–insulator–normal–insulator–superconductor sandwich, fabricated in Nb/Al/AlOx technology. With the nonhysteretic Shapiro steps and the small parameter spread observed, the junctions are suitable for programmable Josephson voltage standards. Their characteristic voltage Vc ≈ 100 μV enables operation at microwave frequencies up to 100 GHz. © 1998 American Institute of Physics.
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74.50.+r Tunneling phenomena; Josephson effects
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
85.25.Cp Josephson devices
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
06.20.F- Units and standards
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Effect of crystallinity on the magnetoresistive properties of La0.8MnO3−δ thin films grown by chemical vapor deposition

S. Pignard, H. Vincent, J. P. Sénateur, K. Fröhlich, and J. Šouc

Appl. Phys. Lett. 73, 999 (1998); http://dx.doi.org/10.1063/1.122065 (3 pages) | Cited 34 times

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We report here a study on the role of crystallinity on the magnetoresistive properties of self-doped La0.8MnO3−δ thin films. Films have been grown by a liquid-source metalorganic chemical vapor deposition technique on two different single crystals: SrTiO3 (001) and Al2O3 (012). Epitaxial films are obtained on strontium titanate and show a high magnetoresistance peak at low fields: maximum magnetoresistive effect in the vicinity of the magnetic transition temperature, and negligible 50 K below. Polycrystalline films are observed on sapphire; they exhibit a lower magnetoresistance of several percent which remains nearly constant over a wide temperature range. Two magnetoresistive regimes can be distinguished in these films: in low fields (up to 5 mT), a strong magnetoresistance is obtained with a sensitivity of 0.28%/mT at 78 K; in higher fields, the magnetoresistance is linear and lower than this obtained in epitaxial films. The role of grain boundaries on the magnetoresistive effect is discussed. © 1998 American Institute of Physics.
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75.47.De Giant magnetoresistance
61.72.Mm Grain and twin boundaries
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.-s Critical-point effects, specific heats, short-range order

Giant magnetoresistance in multilayers electrodeposited on n-Si

A. P. O’Keeffe, O. I. Kasyutich, W. Schwarzacher, L. S. de Oliveira, and A. A. Pasa

Appl. Phys. Lett. 73, 1002 (1998); http://dx.doi.org/10.1063/1.122066 (3 pages) | Cited 21 times

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Co–Ni–Cu/Cu multilayers have been electrodeposited directly onto n-type Si substrates. This removes the need to use a seed-layer deposited by some other method as part of the growth process and makes electrodeposition a significantly more convenient method for fabricating films that exhibit giant magnetoresistance (GMR). A maximum GMR of over 10% and a sensitivity of over 0.04%/Oe were recorded. The GMR and sensitivity of the multilayers both increase with increasing Cu layer thickness. © 1998 American Institute of Physics.
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75.47.De Giant magnetoresistance
81.15.Pq Electrodeposition, electroplating
81.05.Bx Metals, semimetals, and alloys
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
75.50.Cc Other ferromagnetic metals and alloys

Reentrant metal–insulator-type transition induced by high fluence chromium ion implantation of La0.7Ca0.3MnO3 thin films

L. F. Cohen, P. S. I. P. N. de Silva, N. Malde, A. K. M. Akther Hossain, K. A. Thomas, R. Chater, J. D. MacManus-Driscoll, T. Tate, N. D. Mathur, M. G. Blamire, and J. E. Evetts

Appl. Phys. Lett. 73, 1005 (1998); http://dx.doi.org/10.1063/1.122067 (3 pages) | Cited 3 times

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Thin films of colossal magnetoresistance (MR) material La0.7Ca0.3MnO3 were implanted with 200 keV Cr ions over a range of fluence from 1×1013 to 5×1015 ions/cm2. Resistance measurements were made in zero and applied magnetic fields of up to 8 T. At fluences of 1×1014 and 5×1014 Cr+/cm2, the resistance was much greater than in the unimplanted material and the metal–insulator transition temperature was suppressed to values below 20 K. For the highest fluence (5×1015 ions/cm2), a reentrant metal–insulator-type transition was observed and the resistance dropped significantly. Furthermore, improvement in the low-field MR was observed between the virgin and high fluence implanted films for fields less than 500 mT. These results are interpreted in terms of changes in magnetic properties with depth, defect creation, and the influence of oxygen deficiency. © 1998 American Institute of Physics.
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71.30.+h Metal-insulator transitions and other electronic transitions
75.50.Dd Nonmetallic ferromagnetic materials
72.15.Gd Galvanomagnetic and other magnetotransport effects
72.20.My Galvanomagnetic and other magnetotransport effects
75.47.De Giant magnetoresistance
72.60.+g Mixed conductivity and conductivity transitions
61.72.up Other materials
61.80.Jh Ion radiation effects
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.66.Bi Elemental solids
61.66.Dk Alloys
75.70.Ak Magnetic properties of monolayers and thin films

Temperature and bias dependence of magnetoresistance in doped manganite thin film trilayer junctions

J. Z. Sun, D. W. Abraham, K. Roche, and S. S. P. Parkin

Appl. Phys. Lett. 73, 1008 (1998); http://dx.doi.org/10.1063/1.122068 (3 pages) | Cited 46 times

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Thin film trilayer junction of La0.67Sr0.33MnO3-SrTiO3-La0.67Sr0.33MnO3 shows a factor of 9.7 change in resistance, in a magnetic field around 100 Oe at 14 K. The junction magnetoresistance is bias and temperature dependent. The energy scales associated with bias and temperature dependence are an order of magnitude apart. The same set of energies also determine the bias and temperature dependence of the differential conductance of the junction. We discuss these results in terms of metallic cluster inclusions at the junction-barrier interface. © 1998 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Dd Nonmetallic ferromagnetic materials
73.61.Ng Insulators
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
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