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10 Jul 1995

Volume 67, Issue 2, pp. 149-296

Page 2 of 2 Pages Previous Page | Jump to Page

Evolution of strain relaxation in compositionally graded Si1−xGex films on Si(001)

J. H. Li, E. Koppensteiner, G. Bauer, M. Hohnisch, H.‐J. Herzog, and F. Schäffler

Appl. Phys. Lett. 67, 223 (1995); http://dx.doi.org/10.1063/1.114674 (3 pages) | Cited 16 times

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High‐resolution x‐ray reciprocal space mapping was employed to determine the in‐depth strain distribution of Si1−xGex films with linear composition gradings between 4.2% and 15% Ge per μm, and thicknesses between 0.4 and 1.7 μm. The variation of grading and thickness parameters of the samples provides a complete picture of the overall relaxation behavior of linearly graded epilayers. The x‐ray data show a top layer of grading‐dependent residual strain whereas the lower parts of the films are completely and/or partly relaxed with respect to the Si substrate. © 1995 American Institute of Physics.
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68.55.-a Thin film structure and morphology

On the nanostructure of pure amorphous silicon

D. L. Williamson, S. Roorda, M. Chicoine, R. Tabti, P. A. Stolk, S. Acco, and F. W. Saris

Appl. Phys. Lett. 67, 226 (1995); http://dx.doi.org/10.1063/1.114675 (3 pages) | Cited 39 times

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New features of the nanoscale structure of amorphous (a)‐Si produced by ion‐implantation‐induced amorphization of crystalline (c)‐Si have been determined by the technique of small‐angle x‐ray scattering (SAXS). Si ion energies up to 17 MeV were used to generate a thick amorphous layer (8 μm) on a c‐Si wafer to enable the SAXS measurements. As‐implanted and thermally annealed (up to 540 °C) a‐Si were studied. No nanovoids were detected within a sensitivity of 0.1 vol %, but the atomic‐scale structure produced a measurable diffuse scattering signal that decreased with increasing anneal temperatures. These measurements show that the known density deficit of 1.8% in a‐Si relative to c‐Si cannot be due to voids and that a‐Si is homogeneous on nm length scale. © 1995 American Institute of Physics.
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61.05.cf X-ray scattering (including small-angle scattering)
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.
61.43.Dq Amorphous semiconductors, metals, and alloys
61.80.Jh Ion radiation effects

Intercascade annihilation of freely migrating defects

A. Iwase, L. E. Rehn, P. M. Baldo, and L. Funk

Appl. Phys. Lett. 67, 229 (1995); http://dx.doi.org/10.1063/1.114676 (3 pages) | Cited 9 times

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To characterize putative interactions between freely migrating defects (FMD) and remnants of energetic displacement cascades, radiation‐induced segregation (RIS) in Cu‐1 at. % Au was measured by Rutherford backscattering during separate and simultaneous irradiation at 400 °C with 1.5 MeV He and 800 keV Cu ions. The strong RIS observed during only He irradiation was greatly reduced under simultaneous Cu irradiation at approximately the same displacements per atom rate; increasing the Cu flux by a factor of 5 suppressed the RIS from the He beam almost completely. The suppression of RIS at 400 °C disappeared quickly when the Cu irradiation ceased. These results demonstrate that a transient population of interstitial and/or vacancy clusters from the Cu irradiation greatly reduces the survival rate of FMD produced by the He. © 1995 American Institute of Physics.
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61.80.Jh Ion radiation effects
61.72.Yx Interaction between different crystal defects; gettering effect
66.30.Fq Self-diffusion in metals, semimetals, and alloys

Electric‐field‐induced exciton transport in coupled quantum well structures

M. Hagn, A. Zrenner, G. Böhm, and G. Weimann

Appl. Phys. Lett. 67, 232 (1995); http://dx.doi.org/10.1063/1.114677 (3 pages) | Cited 30 times

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We report a conceptionally new approach to achieve electrostatically induced transport and confinement for spatially indirect excitons. Experimentally, exciton transport is demonstrated in an electric‐field‐tunable GaAs/AlAs coupled quantum well structure, which is configured as a three‐terminal device. In spatially resolved photoluminescence experiments, it is shown that indirect excitons experience a drift field, which is given by an electrostatically induced band‐gap gradient in the plane of the coupled quantum well structure. © 1995 American Institute of Physics.
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71.35.-y Excitons and related phenomena
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors

Incorporation kinetics of rare‐earth elements in Si during molecular beam epitaxy

K. Miyashita, Y. Shiraki, D. C. Houghton, and S. Fukatsu

Appl. Phys. Lett. 67, 235 (1995); http://dx.doi.org/10.1063/1.114678 (3 pages) | Cited 9 times

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Incorporation kinetics of rare‐earth elements (Er,Pr) in Si during solid source molecular beam epitaxy (MBE) is studied using secondary ion mass spectrometry. Pronounced surface segregation is consistently observed both for Er and Pr in normal MBE growth and their segregation tendencies are even stronger than those of typical dopants. Segregant‐assisted growth (SAG) using Sb was successful in significantly reducing the surface segregation of rare‐earth atoms, thereby opening the possibility of establishing layered structures in normal MBE. © 1995 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.uf Ge and Si

Biexcitonic contribution to polarization‐dependent degenerate four‐wave mixing in GaAs quantum wells

G. J. Denton, R. T. Phillips, and G. W. Smith

Appl. Phys. Lett. 67, 238 (1995); http://dx.doi.org/10.1063/1.114679 (3 pages) | Cited 1 time

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We report measurements of the polarization and time‐averaged intensity of four‐wave mixing signals from GaAs quantum wells as functions of the pump beam polarizations, laser photon energy, and optical injection density, the latter covering a range of higher levels than has previously been reported. Excitation of heavy‐hole excitons produced a sin2 variation of the signal intensity as the pump beam polarizations changed from parallel to perpendicular, while injection of light‐hole excitons led to an approximately cos2 dependence. The tuning dependence of the heavy‐hole‐exciton signal revealed a low‐energy signal which is attributed to biexcitons. The dominance of this signal for perpendicular polarization causes the observed sin2 variation of the heavy‐hole‐exciton signal. © 1995 American Institute of Physics.
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78.47.-p Spectroscopy of solid state dynamics
78.66.Fd III-V semiconductors

Growth of buried SiO2 layers in Si by thermal oxidation: Thermodynamic model

U. Gösele, E. Schroer, and J.‐Y. Huh

Appl. Phys. Lett. 67, 241 (1995); http://dx.doi.org/10.1063/1.114680 (3 pages) | Cited 10 times

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Buried oxides in silicon‐on‐insulator (SOI) structures have been reported to grow in thickness by thermally oxidizing the superficial silicon layer. A thermodynamic model is presented which is based on the experimental observation that thermal oxidation leads to an increase of the oxygen interstitial concentration in silicon beyond its normal solubility. This increase is assumed to be proportional to the growth rate of the external thermal oxide. Discrepancies between the only two available sets of data are discussed in terms of different levels of oxidation‐induced supersaturations of silicon self‐interstitials. © 1995 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.65.-b Surface treatments

In situ measurement of AlAs and GaAs refractive index dispersion at epitaxial growth temperature

V. Bardinal, R. Legros, and C. Fontaine

Appl. Phys. Lett. 67, 244 (1995); http://dx.doi.org/10.1063/1.114681 (3 pages) | Cited 8 times

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In situ molecular beam epitaxy control of III–V optoelectronic device growth has been achieved by dynamic optical reflectometry with tunable excitation wavelength, through the use of a titanium:sapphire laser light source. This new multiwavelength reflectometry method was used to determine the values of the AlAs and GaAs refractive indices at growth temperature (600 °C). Index dispersion between 760 and 960 nm is presented and found to be in good agreement with the existing models. © 1995 American Institute of Physics.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

High performance polarization insensitive electroabsorption modulator based on strained GaInAs–AlInAs multiple quantum wells

S. Chelles, R. Ferreira, P. Voisin, and J. C. Harmand

Appl. Phys. Lett. 67, 247 (1995); http://dx.doi.org/10.1063/1.114682 (3 pages) | Cited 9 times

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We report on the polarization independent operation of an electroabsorption guided‐wave modulator based on strained GaInAs–AlInAs multiquantum well structure. The device operates in the 1.5–1.6 μm wavelength range and exhibits very high static performances as illustrated by the measured 15 dB/100 μm extinction ratio for a drive voltage of only 1.25 V. We show that the observed polarization insensitivity of this device is in good agreement with the calculation of the electroabsorption curves. The detailed analysis indicates that significant improvement of the performance is still possible. © 1995 American Institute of Physics.
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42.79.Hp Optical processors, correlators, and modulators
78.66.Fd III-V semiconductors
78.20.Jq Electro-optical effects

Hot‐electron multiquantum well microwave detector operating at room temperature

Stefano Barbieri, Francesco Mango, Fabio Beltram, Marco Lazzarino, and Lucia Sorba

Appl. Phys. Lett. 67, 250 (1995); http://dx.doi.org/10.1063/1.114683 (3 pages) | Cited 5 times

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A new multiquantum well hot‐electron microwave detector is demonstrated. The GaAs–AlGaAs heterostructure was grown by molecular beam epitaxy and tested in the X and K bands. It showed room‐temperature operation with responsivity of several 103 V/W. The operation of the device is based on enhanced thermionic current due to carrier heating by the incident in‐plane polarized microwave electric field. This principle yields a broad frequency range of operation extending up to the millimeter band without significant degradation of the responsivity. © 1995 American Institute of Physics.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
78.66.Fd III-V semiconductors
73.50.Pz Photoconduction and photovoltaic effects

Growth of AlN by metalorganic molecular beam epitaxy

J. D. MacKenzie, C. R. Abernathy, S. J. Pearton, V. Krishnamoorthy, S. Bharatan, K. S. Jones, and R. G. Wilson

Appl. Phys. Lett. 67, 253 (1995); http://dx.doi.org/10.1063/1.114684 (3 pages) | Cited 14 times

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Thin film AlN has been grown on Al2O3 and GaAs substrates by metalorganic molecular beam epitaxy using amine bonded alane precursors and either tertiarybutylamine or nitrogen from a compact electron cyclotron resonance (ECR) plasma source operating at 2.45 GHz. Typical growth pressures were in the 0.5–1×10−4 Torr range. The growth rates, impurity backgrounds, and surface morphologies were examined for both nitrogen sources and both the solid and liquid alanes. In general, growth efficiencies were good for both alane precursors, allowing for deposition of the low temperature, ∼400 °C, AlN buffers needed for subsequent growth of GaN and InGaAlN alloys. Low growth temperatures could not be obtained using tertiarybutylamine, presumably due to poor decomposition efficiency of the source at low temperatures. The structural quality of material grown at high temperatures from the ECR plasma was measured by atomic force microscopy, high resolution x‐ray diffraction, and transmission electron microscopy, indicating single crystal material with a surface roughness of ∼8 Å and an x‐ray full width half‐maximum of 430 arcsec. This ECR plasma‐derived material was of sufficient quality to allow for the growth of multiple quantum well InGaAlN structures. © 1995 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Novel InGaAs/GaAs quantum dot structures formed in tetrahedral‐shaped recesses on (111)B GaAs substrate using metalorganic vapor phase epitaxy

Yoshihiro Sugiyama, Yoshiki Sakuma, Shunichi Muto, and Naoki Yokoyama

Appl. Phys. Lett. 67, 256 (1995); http://dx.doi.org/10.1063/1.114685 (3 pages) | Cited 29 times

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We report a novel GaAs/InGaAs/GaAs quantum dot structure formed in a tetrahedral‐shaped recess (TSR) patterned on a (111)B GaAs substrate with anisotropic chemical etching. The pseudomorphic heterostructure shows two clear photoluminescence peaks which are attributed to an In anisotropic incorporation on (111)B compared to (111)A. Cathodoluminescence at a lower energy peak with InGaAs of 2.5 nm shows a bright image at the bottom of TSRs which indicates the local minimum in potential energy at the bottom of TSR. © 1995 American Institute of Physics.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase

High quality Si1−x−yGexCy epitaxial layers grown on (100) Si by rapid thermal chemical vapor deposition using methylsilane

J. Mi, P. Warren, P. Letourneau, M. Judelewicz, M. Gailhanou, M. Dutoit, C. Dubois, and J. C. Dupuy

Appl. Phys. Lett. 67, 259 (1995); http://dx.doi.org/10.1063/1.114686 (3 pages) | Cited 51 times

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We have produced epitaxial Si1−x−yGexCy/Si heterostructures by rapid thermal chemical vapor deposition using methylsilane SiCH6). These layers were grown in the SiH4/GeH4/SiCH6/H2 system between 550 and 600 °C at 1.5 Torr. Suitable process conditions were found that allow very efficient substitutional carbon incorporation. No carbon cross contamination was observed. Crystal quality, chemical composition, and lattice strain were deduced from Nomarski microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, secondary ion mass spectrometry, and x‐ray diffraction. Defect‐free alloy layers with compositions of up to 20 at.% Ge and 2.2 at. % C were produced. The lattice parameter was tailored so that the strain in these layers gradually moved from compressive to tensile. A tensile strain of up to 0.35% was achieved. © 1995 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

On‐wafer characterization of In0.52Al0.48As/In0.53Ga0.47As modulation‐doped field‐effect transistor with 4.2 ps switching time and 3.2 ps delay

A. Zeng, M. K. Jackson, M. Van Hove, and W. De Raedt

Appl. Phys. Lett. 67, 262 (1995); http://dx.doi.org/10.1063/1.114687 (2 pages) | Cited 7 times

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We report fabrication and electro‐optic measurement of In0.52Al0.48As/In0.53Ga0.47As modulation‐ doped field‐effect transistors. The devices are monolithically integrated with coplanar stripline fixtures incorporating photoconductive switches. The switching time for a 0.35 μm T‐gate device is 4.2 ps and the delay is 3.2 ps. This is the fastest directly measured switching in a three‐terminal device reported to date. © 1995 American Institute of Physics.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Ultrafast energy loss of electrons in p‐GaAs

R. Rodrigues‐Herzog, M. Sailer, N. E. Hecker, R. A. Höpfel, N. Nintunze, and M. A. Osman

Appl. Phys. Lett. 67, 264 (1995); http://dx.doi.org/10.1063/1.114777 (3 pages) | Cited 8 times

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We investigated the ultrafast energy relaxation of photoexcited minority electrons in highly doped p‐GaAs by means of femtosecond time resolved luminescence (Δt<90 fs). Our experiments allow the first observation of the extremely fast cooling of minority electrons within the Γ‐valley. The electron mean energy decreases within 150 fs from 150 meV down to less than 50 meV. The total energy loss rate reaches values higher than 10−7 W per electron, representing the highest energy loss rates of electrons observed to date in monocrystalline semiconductors. Ensemble Monte Carlo simulations show that the electron‐hole scattering is responsible for these high energy loss rates. © 1995 American Institute of Physics.
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78.47.-p Spectroscopy of solid state dynamics
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Surface‐mode stimulated emission from optically pumped GaInN at room temperature

S. T. Kim, H. Amano, and I. Akasaki

Appl. Phys. Lett. 67, 267 (1995); http://dx.doi.org/10.1063/1.114778 (3 pages) | Cited 22 times

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In this letter, we report the surface‐mode stimulated emission from optically pumped Ga0.11In0.89N at room temperature. The GaInN was deposited on the intermediate layer of GaN grown on the AlN buffer layer over sapphire substrate using horizontal metalorganic vapor phase epitaxy method. The peak wavelength and the full width at half‐maximum of surface‐mode stimulated emission was 406 nm and 25.6 meV, respectively, and the threshold of excitation power density was about 0.52 MW/cm2. © 1995 American Institute of Physics.  
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78.45.+h Stimulated emission
78.66.Fd III-V semiconductors
42.55.Px Semiconductor lasers; laser diodes

Molecular beam epitaxy of p‐type conducting ZnSe and ZnSSe by simple nitrogen gas doping without plasma activation

Yuji Hishida, Tomoyuki Yoshie, Katsumi Yagi, Keiichi Yodoshi, and Tatsuhiko Niina

Appl. Phys. Lett. 67, 270 (1995); http://dx.doi.org/10.1063/1.114779 (3 pages)

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Highly conducting p‐type ZnSe and ZnSSe were fabricated by simple N2 gas doping during molecular beam epitaxial growth without the use of any activation method, such as discharge and cracking. p‐type conduction in the N2‐gas doped ZnSe is produced by a shallow N acceptor state, which is obtained only when the dopant N2 pressure is higher than 10−5 Torr. When the N2 pressure was varied from 3.2×10−5 to 1×10−4 Torr, the net acceptor concentration of N2‐gas doped ZnSe and ZnS0.06Se0.94 films ranged from 3×1015 to 2×1017 cm−3 and from 1×1016 to 2.5×1017 cm−3, respectively. Light emitting diodes with a N2‐gas doped p‐cladding layer were fabricated and tested. © 1995 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.61.Ga II-VI semiconductors

PdGeTiPt Ohmic contacts to p+‐AlxGa1−xAs

W. Y. Han, M. W. Cole, L. M. Casas, K. A. Jones, H. S. Lee, M. Wade, A. DeAnni, A. Lapore, Y. Lu, and L. W. Yang

Appl. Phys. Lett. 67, 273 (1995); http://dx.doi.org/10.1063/1.114780 (3 pages)

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Ohmic contacts to heavily C‐doped AlGaAs were made using PdGeTiPt that had specific contact resistances Rc, as low as 1.7×10−6 Ω cm2 when annealed at 600 °C. The less heavily doped samples annealed at temperatures between 350 and 500 °C were non‐Ohmic, and Rc decreased with increasing annealing temperature between 500 and 600 °C. For the more heavily doped samples, Rc decreased with increasing annealing temperature. Rc increased for all samples at annealing temperatures above 600 °C. Rc rose quickly by 102 when the samples were reannealed at 300 °C for 20 h, but remained unchanged with further reannealing for up to 100 h. This behavior is consistent with partial compensation generated by the rapid out‐diffusion of Ga at low annealing temperatures and the subsequent in‐diffusion of Ge into the Ga vacancies left behind. The lower Rc obtained with the 600 °C anneal can be explained by an increased As out‐diffusion and the subsequent in‐diffusion of Ge into the As vacancies at the higher annealing temperatures. Interfacial reactions and elemental diffusion of the contacts investigated via transmission electron microscopy and elemental depth profiles obtained by Auger electron spectroscopy are also consistent with this mode. © 1995 American Institute of Physics.
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73.40.Cg Contact resistance, contact potential
73.40.Ns Metal-nonmetal contacts

Quantitative Auger electron spectroscopic analysis of Ge surface segregation in Si/Ge/Si(100) heterostructures

Yun Li, G. G. Hembree, and J. A. Venables

Appl. Phys. Lett. 67, 276 (1995); http://dx.doi.org/10.1063/1.114781 (3 pages) | Cited 13 times

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Germanium surface segregation in Si/Ge/Si(100) heteroepitaxial structures has been studied by quantitative Auger electron spectroscopy (AES) and reflection high energy electron diffraction (RHEED). Ge segregation was measured for 1–4 ML Ge, for slow Si growth rates (3×10−4 nm/s) at moderate deposition temperature (520 °C). A layer growth model is used to infer segregation probabilities between 90% and 98%, increasing with Ge layer thickness, especially between 1 and 2 ML. Using this model, the Ge profile in the cap layer is calculated. Surface roughness is just noticeable at 4 ML, and is incorporated into the model in an illustrative manner. A two‐state model is used to determine the segregation energy, 0.24±0.02 eV, for 2–3 ML. © 1995 American Institute of Physics.
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68.55.-a Thin film structure and morphology

Native point defects in low‐temperature‐grown GaAs

X. Liu, A. Prasad, J. Nishio, E. R. Weber, Z. Liliental‐Weber, and W. Walukiewicz

Appl. Phys. Lett. 67, 279 (1995); http://dx.doi.org/10.1063/1.114782 (3 pages) | Cited 122 times

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We present structural and electronic data which indicate that the dominant defects in GaAs grown at low temperatures (LT GaAs) by molecular beam epitaxy (MBE) are As antisites (AsGa) and Ga vacancies (VGa), with negligible amounts of As interstitials (Asi). We show that the change of lattice parameter correlates with the concentration of AsGa, and that AsGa alone can account for the lattice expansion. We also show that the total concentration of AsGa has a characteristic second power dependence on the concentration of AsGa in the positive charge state for the material grown at different temperatures. This can be understood provided that VGa defects are the acceptors responsible for the carrier compensation. Our results are consistent with most experimental results and the theoretical expectation from the calculation of defect formation energies. We find that the conclusion may also be true in As‐rich bulk GaAs. © 1995 American Institute of Physics.
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61.72.J- Point defects and defect clusters
71.55.Eq III-V semiconductors
78.30.-j Infrared and Raman spectra
78.40.Fy Semiconductors
78.70.Ck X-ray scattering

Voltage divider based on submicron slits in a high Tc superconducting film and two bicrystal grain boundaries

V. K. Kaplunenko, Z. G. Ivanov, E. A. Stepantsov, T. Claeson, and E. Wikborg

Appl. Phys. Lett. 67, 282 (1995); http://dx.doi.org/10.1063/1.114783 (3 pages) | Cited 31 times

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Experiments on a model of rapid single flux quantum (RSFQ) flip‐flop cell, based on high‐Tc (HTS) Josephson junctions show that it can operate as a voltage divider at frequency up to 400 GHz. The junctions were formed in YBaCuO film, deposited on novel Y–ZrO2 bicrystals with two asymmetric 32° grain boundaries, about 10 μm apart, and allow a new design of RSFQ logic based on a single HTS layer. Small inductances (≂10 pH) were made as narrow, submicron size slits. The junction widths were between 4 and 10 μm and for ten junctions located close to the tested circuits, the linear critical current densities at T=4.4 K were 10.7 μA/μm±50% for one grain boundary and 8.3 μA/μm±50% for the other one. IcRn was about 1 mV±50%. A current density of half the expected value meant that the test circuit did not act as an ideal flip–flop down to the lowest frequency. As a voltage divider it gave a half value division up to 0.82 mV at T=4.4 K and to 0.4 mV at 30 K. © 1995 American Institute of Physics.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)

Electro‐optic sampling of 1.5‐ps photoresponse signal from YBa2Cu3O7−δ thin films

F. A. Hegmann, D. Jacobs‐Perkins, C.‐C. Wang, S. H. Moffat, R. A. Hughes, J. S. Preston, M. Currie, P. M. Fauchet, T. Y. Hsiang, and Roman Sobolewski

Appl. Phys. Lett. 67, 285 (1995); http://dx.doi.org/10.1063/1.114784 (3 pages) | Cited 30 times

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Photoresponse signals with widths as short as 1.5 ps are observed from epitaxial YBa2Cu3O7−δ  thin films using electro‐optic sampling techniques. Voltage transients less than 2 ps wide are seen in 100‐ and 200‐nm films exposed to 150‐fs laser pulses and cooled to 79 K. At low bias currents, the amplitude of the fast response varies linearly with the bias current, suggesting a kinetic inductive mechanism. A negative transient about 15‐ps long is also seen that may provide evidence for nonequilibrium recombination of excited quasiparticles into Cooper pairs. At high bias currents or large laser fluences, a fast tail with a decay time of about 10 ps appears in the response followed by a slow, resistive bolometric component due to sample heating. Nonequilibrium aspects of the photoresponse and the origin of the fast tail are discussed. © 1995 American Institute of Physics.
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74.25.N- Response to electromagnetic fields
74.78.-w Superconducting films and low-dimensional structures
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.25.Dq Superconducting quantum interference devices (SQUIDs)

Stability of growing front of YBa2Cu3Ox superconductor in the presence of Pt and CeO2 additions

Gregory Kozlowski and Thomas Svobodny

Appl. Phys. Lett. 67, 288 (1995); http://dx.doi.org/10.1063/1.114785 (3 pages) | Cited 4 times

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Distinctive microstructures of textured YBa2Cu3Ox (123) superconductors were examined by scanning electron microscopy and metallurgical microscopy. The samples were synthesized under a residual thermal gradient by using a modified melt textured growth on a Y2BaCuO5 (211) substrate. Also, the unidirectional solidification by a zone‐melting method was performed to fabricate 123 superconducting bars up to 12 cm long placed on the 211 substrate in the horizontal arrangement, with a growth rate R=0.5 mm/h and a temperature gradient of G=20 °C/cm (G/R=400 °C h/cm2). A ramping temperature of 1 °C/h (GR) was applied in both syntheses. Typical defects running parallel to (001) planes associated with 211 trapped particles were observed (so‐called platelet structure). Besides these, unusual defects were observed running parallel to (100) and (010) planes in textured 123+Pt superconductors, and interpreted as the result of an instability of the planar front in the presence of fine 211 particles. A theoretical model of planar interface stability confirms a strong dependence of stability region on the size of 211 particles in the melt. © 1995 American Institute of Physics.
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81.10.Fq Growth from melts; zone melting and refining
74.72.-h Cuprate superconductors
81.10.Aj Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation

Magnetic field induced broadening of the resistive transition in epitaxial c‐axis‐oriented HgBa2CaCu2O6+δ films

M. Rupp, A. Gupta, and C. C. Tsuei

Appl. Phys. Lett. 67, 291 (1995); http://dx.doi.org/10.1063/1.114786 (3 pages) | Cited 16 times

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The resistive transition in epitaxial c‐axis‐oriented HgBa2CaCu2O6+δ (Hg‐1212) thin films Tc∼122 K) in magnetic fields up to 9 T have been investigated. A considerably larger broadening of the resistive transition is observed for magnetic fields perpendicular to the ab plane than for fields parallel to the ab plane. Over the measured range of magnetic fields, the resistivity exponentially approaches zero as a function of decreasing temperature, suggesting a thermally activated flux creep behavior. The anisotropic characteristics of Hg‐1212 are compared with other high‐temperature cuprate superconductors and found to be less than for the Bi or Tl two‐layer systems, but still considerably larger than for YBa2Cu3O7−δ. This can be qualitatively explained on the basis of the differences in the insulator spacing layer thickness between the adjacent CuO2 layers in these cuprates. © 1995 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)

High‐current superconducting Tl1Ba2Ca2Cu3Oy thick films on polycrystalline Ag by spin coating

Qing He, D. K. Christen, C. E. Klabunde, J. E. Tkaczyk, K. W. Lay, M. Paranthaman, J. R. Thompson, A. Goyal, A. J. Pedraza, and D. M. Kroeger

Appl. Phys. Lett. 67, 294 (1995); http://dx.doi.org/10.1063/1.114787 (3 pages) | Cited 6 times

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Thick films of the high‐temperature superconductor Tl1Ba2Ca2Cu3Oy with high current density Jc have been deposited on polycrystalline Ag substrates by a spin‐coating method. The spin‐coated precursor films were annealed in a two‐zone Tl reaction furnace. Film thicknesses ranged from 10 to 30 μm, leading to good total current capabilities. The films have highly‐textured c‐orientation as evidenced by rocking curves with FWHM of 4° for the (006) peak. Scanning electron micrographs revealed a dense, plate‐like layered structure and almost no reaction between the film and the Ag substrate. Values of Jc (77 K) up to 2.5×104 A/cm2 in zero field and more than 1000 A/cm2 in a 1 tesla field (H∥c axis). © 1995 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
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