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7 Sep 1992

Volume 61, Issue 10, pp. 1145-1248

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Ge segregation and its suppression in GaAs epilayers grown on Ge(111) substrate

T. Kawai, H. Yonezu, H. Yoshida, and K. Pak

Appl. Phys. Lett. 61, 1216 (1992); http://dx.doi.org/10.1063/1.107599 (3 pages) | Cited 11 times

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The interdiffusion of the compositional atoms was investigated at heterointerface between a GaAs epilayer and a Ge(111) substrate by secondary ion mass spectroscopy. When a thin AlAs layer is applied initially, diffusion of Ge into the GaAs epilayer was suppressed effectively. An abrupt heterointerface was successfully realized in relatively high temperature growth. The interdiffusion process at the AlAs‐Ge heterointerface was clarified in high temperature growth, which was dominated by the temperature‐assisted segregation of Ge atoms during the AlAs growth rather than thermal diffusion. The compositional diffusion of Al atoms into the GaAs epilayer was also observed, which was enhanced by the Ge segregation in the structure of GaAs/AlAs/Ge substrate grown at higher temperature.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
68.35.Fx Diffusion; interface formation
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Vacuum‐deposited metal/polyaniline Schottky device

S. C. K. Misra, M. K. Ram, S. S. Pandey, B. D. Malhotra, and Subhas Chandra

Appl. Phys. Lett. 61, 1219 (1992); http://dx.doi.org/10.1063/1.107600 (3 pages) | Cited 37 times

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All vacuum‐deposited metal/semiconducting polyaniline hetrojunction Schottky devices using vacuum‐evaporated polyaniline films of a thickness of the order of 0.1 μm have been prepared. Schottky junctions have been formed using the following metals, Al, Sn, In, Pb, Sb, and Ag. Electrical characterization has been carried out and electronic parameters, including the barrier height and ideality factor, have been determined. Infrared optical absorption spectroscopy of the vacuum‐deposited polyaniline films were used to determine the structure, energy band gap, and effect of various ambients on the vacuum‐deposited polyaniline films.
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85.30.Hi Surface barrier, boundary, and point contact devices
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
73.61.Cw Elemental semiconductors
73.61.Jc Amorphous semiconductors; glasses
73.61.Le Other inorganic semiconductors
73.40.Ns Metal-nonmetal contacts

Gallium desorption during growth of (Al,Ga)As by molecular beam epitaxy

J.‐P. Reithmaier, R. F. Broom, and H. P. Meier

Appl. Phys. Lett. 61, 1222 (1992); http://dx.doi.org/10.1063/1.107601 (3 pages) | Cited 13 times

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A new two‐phase model for gallium desorption can quantitatively explain the change of the desorption energy as a function of the III/V ratio. In this model, the gallium loss rate is described as a phenomenon of simultaneous desorption from a Ga fluid state and a GaAs solid state. This behavior was experimentally verified by accurate thickness measurements of epitaxial AlxGa1−xAs layers by transmission electron microscopy. The results show the Ga loss rate is directly dependent only on the Ga coverage on the surface, while the desorption energy is independent of the aluminum concentration. By varying the III/V ratio, we found that the Ga desorption energy increases from 3.1 eV at low arsenic flux to 4.7 eV at high arsenic flux.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics

Photoluminescence characterization of gated pseudomorphic AlGaAs/InGaAs/GaAs modulation‐doped field‐effect transistors

J. M. Gilpérez, J. L. Sánchez‐Rojas, E. Muñoz, E. Calleja, J. P. R. David, G. Hill, and J. Castagné

Appl. Phys. Lett. 61, 1225 (1992); http://dx.doi.org/10.1063/1.107602 (3 pages) | Cited 19 times

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Electric field effects on gated pseudomorphic AlGaAs/InGaAs/GaAs quantum wells, where the Fermi level is modulated with a reverse gate voltage, are studied by low‐temperature photoluminescence. A fit of the measured transition energies, with a self‐consistent solution of the coupled Schrödinger–Poisson equations, gives the Fermi energy and the sheet carrier density. The absolute and relative intensities, from the first and second electron subbands to the first‐hole subband transitions, are analyzed as a function of the carrier density and the Fermi level position. A very good agreement is found between data and calculations. No photoluminescence intensity enhancement, assigned to the Fermi‐energy‐edge singularity effects, has been observed.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling
78.55.Cr III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Nb Josephson junction with an AlNx barrier made by plasma nitridation

Tetsuyoshi Shiota, Takeshi Imamura, and Shinya Hasuo

Appl. Phys. Lett. 61, 1228 (1992); http://dx.doi.org/10.1063/1.107603 (3 pages) | Cited 18 times

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We studied Nb junctions with aluminum nitride, AlNx, tunnel barriers formed by plasma nitridation on aluminum film surfaces. The AlNx barrier junctions show current‐voltage characteristics with leakage currents small enough and critical current densities large enough for use in Josephson digital circuits. The AlNx barrier junction exhibited improved annealing stability as compared to AlOx barrier junctions. For the AlNx barrier junction, decreases in critical current during annealing at 250 °C are remarkably suppressed.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
74.50.+r Tunneling phenomena; Josephson effects
81.05.Bx Metals, semimetals, and alloys

Planar microwave biased radio frequency SQUIDs with a cryogenic preamplifier

M. Mück, G. Hallmanns, C. Heiden, G. Fontana, M. Cerdonio, R. Mezzena, and S. Vitale

Appl. Phys. Lett. 61, 1231 (1992); http://dx.doi.org/10.1063/1.107604 (3 pages) | Cited 2 times

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We report on the design and performance of a planar microwave rf‐SQUID readout by a cryogenic preamplifier. The SQUID‐sensor consists of a planar half‐wavelength microstrip resonator, into which the SQUID‐loop is integrated. The pump frequency is 1.7 GHz. The cryogenic preamplifier employs a microwave high electron mobility transistor (HEMT), located close to the SQUID sensor. Measurements of the flux noise and the fractional step rise parameter were carried out in the temperature range between 4.2 and 1.5 K. In an open loop white flux noise values of 2×10−6 Φ0/√Hz were obtained at 4.2 K.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
74.50.+r Tunneling phenomena; Josephson effects

(001) faceting and Bi2Sr2CuO6+x(Tc=7–22 K) phase formation at the Ag/Bi‐Sr‐Ca‐Cu‐O interface in Ag‐clad Bi2Sr2CaCu2O8+x(Tc=75–95 K) superconducting tapes

Y. Feng, D. C. Larbalestier, S. E. Babcock, and J. B. Vander Sande

Appl. Phys. Lett. 61, 1234 (1992); http://dx.doi.org/10.1063/1.107605 (3 pages) | Cited 10 times

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The Ag/Bi‐Sr‐Ca‐Cu‐O (BSCCO) interface in Ag‐clad Bi‐2212 tapes was investigated by high‐resolution transmission electron microscopy. The interface was found to be well bonded and free of nonsuperconducting second phases. However, a one‐half‐unit‐cell‐thick layer of the Bi‐2201 phase was observed between the Bi‐2212 phase and the Ag‐cladding. A very strong texturing of the (001) planes of the BSCCO parallel to the Ag was seen. When the interface was nearly parallel to the Bi‐2212 (001) planes, it tended to facet onto (001), leaving steps of height equal to one‐half the Bi‐2201 lattice spacing. Thus, strong (001) texturing extends to the atomic scale.
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84.71.Ba Superconducting magnets; magnetic levitation devices
74.70.-b Superconducting materials other than cuprates
68.35.Fx Diffusion; interface formation

Order‐of‐magnitude method for estimating the fluence that optimizes the critical current in particle‐irradiated cuprate superconductors

B. D. Weaver and G. P. Summers

Appl. Phys. Lett. 61, 1237 (1992); http://dx.doi.org/10.1063/1.107606 (3 pages) | Cited 2 times

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The particle fluence that maximizes the critical current enhancement in cuprate superconductors is shown to be closely related to the nonionizing energy loss (displacement damage) of a given particle. In many cases, only the incident particle type and energy need to be known in order to allow an order‐of‐magnitude prediction of the optimal fluence for enhancing the critical current.
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74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition

Orientation relationships of epitaxial oxide buffer layers on silicon (100) for high‐temperature superconducting YBa2Cu3O7−x films

Th. Matthée, J. Wecker, H. Behner, G. Friedl, O. Eibl, and K. Samwer

Appl. Phys. Lett. 61, 1240 (1992); http://dx.doi.org/10.1063/1.107607 (3 pages) | Cited 38 times

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The preparation parameters of epitaxially grown buffer layers on silicon (100) wafers were investigated. We found that an in situ removal of the native amorphous SiO2 layer from the Si surface is possible, avoiding the etching of the wafer prior to the deposition. YSZ and Y2O3 were chosen as buffer layers for subsequent YBa2Cu3O7−x thin‐film deposition. The orientation of the thin films during the deposition process was analyzed by RHEED. Different orientations on the substrates are obtained depending on the evaporation parameters. TEM studies of the interfaces, x‐ray diffraction analysis, and measurements of the superconducting properties were made after the deposition of the films.
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68.55.-a Thin film structure and morphology
74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates

YBa2Cu3O7−δ films on Si with Y‐stabilized ZrO2 and Y2O3 buffer layers: High‐resolution electron microscopy of the interfaces

A. Bardal, M. Zwerger, O. Eibl, J. Wecker, and Th. Matthée

Appl. Phys. Lett. 61, 1243 (1992); http://dx.doi.org/10.1063/1.107608 (3 pages) | Cited 14 times

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The interfaces of YBa2Cu3O7−δ (YBCO) thin films grown on Si substrates with Y‐stabilized ZrO2 (YSZ) and Y2O3 buffer layers have been studied by high‐resolution electron microscopy. At the Si‐YSZ interfaces a 4‐nm‐thick amorphous silica layer is found, bridged by 10‐nm‐wide crystalline YSZ regions. Close to these regions the Si substrate contains planar {111} faults. At the YSZ‐Y2O3 interfaces perfect misfit dislocations are present, with Burgers vector 1/2〈110〉. They occur either as separated single dislocations or as separated groups of closely spaced dislocations. The atomic coordination at the planar and atomically sharp Y2O3‐YBCO interface could be revealed. The first atomic layer of the YBCO is found to be a Ba layer.
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07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination
68.55.-a Thin film structure and morphology
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
74.70.-b Superconducting materials other than cuprates

Property modification of ferroelectric Pb(Zr,Ti)O3 thin films by low‐energy oxygen ion bombardment during film growth

H. Hu and S. B. Krupanidhi

Appl. Phys. Lett. 61, 1246 (1992); http://dx.doi.org/10.1063/1.107609 (3 pages) | Cited 14 times

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Low‐energy oxygen ion bombardment is being used to enhance the electrical properties of multi‐ion beam sputter deposited ferroelectric Pb(Zr,Ti)O3 thin films. The degree of (100) orientation, remnant polarization (Pr), coercive field (Ec), and dielectric constant (k) of the films were chosen to properly quantify the bombardment effect. It was found that these properties are strongly dependent on the ion beam flux and bombarding ion energy. The ion/atom ratios between 1.0 and 1.3 and the bombarding energies within the range of 60–80 eV are optimal to realize desirable property modification. Relative to the nonbombarding case, the bombardment could increase the Pr and k by up to 60% and 25%, respectively, and reduce the Ec by about 20%.
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61.80.Jh Ion radiation effects
77.55.-g Dielectric thin films
81.15.Cd Deposition by sputtering
77.80.-e Ferroelectricity and antiferroelectricity
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