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7 Jun 1993

Volume 62, Issue 23, pp. 2899-3051

Page 2 of 3 Pages Previous Page Next Page | Jump to Page

Effect of point defect reactions on behavior of boron and oxygen in degenerately doped Czochralski silicon

W. Wijaranakula

Appl. Phys. Lett. 62, 2974 (1993); http://dx.doi.org/10.1063/1.109161 (3 pages) | Cited 3 times

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The behavior of boron and oxygen in degenerately doped Czochralski silicon has been studied after an extended annealing at temperatures ranging between 750 and 900 °C in nitrogen ambient. The results from secondary ion mass analysis show an accumulation of boron atoms near the silicon surface while oxygen outdiffusion appears to be significantly retarded. Based upon the defect morphology examined using high resolution electron microscopy, it is concluded that degenerate silicon is saturated with interstitial defect species during an extended annealing. From the point defect reaction and dynamic clustering models, an accumulation of boron near the silicon surface is hypothesized to be due to boron outdiffusion which may be driven by the difference in chemical potential of boron saturation between the bulk and surface regions. A retardation of oxygen diffusion, on the other hand, may be caused by a strong pairing reaction between boron and oxygen atoms.
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61.72.Cc Kinetics of defect formation and annealing
61.72.uf Ge and Si
61.72.Yx Interaction between different crystal defects; gettering effect
66.30.J- Diffusion of impurities

Si3N4/Si/n‐GaAs capacitor with minimum interface density in the 1010 eV−1 cm−2 range

Z. Wang, M. E. Lin, D. Biswas, B. Mazhari, N. Teraguchi, Z. Fan, X. Gui, and H. Morkoç

Appl. Phys. Lett. 62, 2977 (1993); http://dx.doi.org/10.1063/1.109162 (3 pages) | Cited 24 times

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We report significant improvements in the electrical characteristics of Si3N4/Si/GaAs capacitors with the assistance of atomic hydrogen during the in situ growth of Si on GaAs. Si3N4/Si/GaAs capacitors have shown a minimum interface state density as low as 3×1010 eV−1 cm−2 as determined by the low‐frequency capacitance method. The hysteresis and frequency dispersion in the GaAs metal‐insulator‐semiconductor capacitor are very small (200 and 100 meV, respectively). These results represent significant advances over previous reports.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.30.Tv Field effect devices
73.20.At Surface states, band structure, electron density of states
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Imaging‐plate plane‐wave x‐ray topography of local lattice distribution due to growth striations in silicon crystals

I. Maekawa, Y. Kudo, S. Kojima, S. Kawado, and T. Ishikawa

Appl. Phys. Lett. 62, 2980 (1993); http://dx.doi.org/10.1063/1.109163 (3 pages) | Cited 4 times

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A newly developed imaging‐plate plane‐wave x‐ray topography (IPPWT) method has been successfully applied to the quantitative analysis of local lattice distortion due to growth striations in magnetic‐field‐applied Czochralski silicon single crystals. IPPWT was found to possess sufficient spatial resolution to accurately measure variations of growth‐induced local lattice distortions (Δd/d and Δα). The advantageous features of IPPWT, in comparison with conventional photographic‐plate plane‐wave x‐ray topography, are a wide latitude in x‐ray exposure conditions, better x‐ray intensity linearity for performing quantitative analysis, and convenience in image processing and data handling.
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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.
61.66.Bi Elemental solids
61.72.Dd Experimental determination of defects by diffraction and scattering

Epitaxial growth of (Hg,Mn)Te by the interdiffused multilayer process

M. Funaki, A. W. Brinkman, T. D. Hallam, and B. K. Tanner

Appl. Phys. Lett. 62, 2983 (1993); http://dx.doi.org/10.1063/1.109164 (3 pages) | Cited 1 time

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Epitaxial films of (Hg,Mn)Te have been grown by metalorganic vapor phase epitaxy using the interdiffused multilayer process (IMP), on GaAs (100) substrates with a ∼1 μm buffer layer of CdTe. In order to grow the MnTe component, it was found necessary to grow at 380 °C with a precursor partial pressure ratio (Mn:Te) of 5–8. The IMP layers were found to be more uniform in composition and thickness than comparable layers of (Hg,Mn)Te grown by the more conventional direct alloy growth method. X‐ray rocking curve widths for IMP layers were typically ∼200″ with a variation across the layer of ∼10%. Variations in composition were <10%.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
66.30.Ny Chemical interdiffusion; diffusion barriers

Band‐gap narrowing determination by photoluminescence on strained B‐doped Si0.82Ge0.18 layers grown on Si

A. Souifi, G. Brémond, T. Benyattou, G. Guillot, D. Dutartre, and P. Warren

Appl. Phys. Lett. 62, 2986 (1993); http://dx.doi.org/10.1063/1.109165 (3 pages) | Cited 9 times

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This work reports on photoluminescence (PL) characterization of heavy boron‐doped SiGe(p+)/Si(p) heterostructures and Si(p+)/Si(p) pseudoheterostructures grown by rapid thermal chemical vapor deposition. For the pseudoheterostructures, the band‐gap narrowing is measured in the 4×1018–1.5×1019 cm−3 doping level range in very good agreement with bulk silicon results. The band‐gap narrowing of SiGe strained layers has been determined for the first time, by means of PL measurements on boron‐doped Si0.82Ge0.18 strained alloy up to 4×1019 cm−3. The reduced band gap of the Si0.82Ge0.18 alloy is deduced, taking into account both strain and heavy doping effects and compared to band‐gap narrowing found in Si.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.55.Hx Other solid inorganic materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

10 nm electron beam lithography and sub‐50 nm overlay using a modified scanning electron microscope

P. B. Fischer and S. Y. Chou

Appl. Phys. Lett. 62, 2989 (1993); http://dx.doi.org/10.1063/1.109166 (3 pages) | Cited 39 times

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Gratings of 10 nm wide metal lines 30 nm apart, and quantum transistor gates with 10 nm wide gaps over 300 nm long between two metal rectangles have been repeatedly achieved on thick GaAs substrates using a modified scanning electron microscope operated at 35 keV and liftoff of Ni/Au. Furthermore, multilevel electron beam lithography with a standard deviation (3σ) of an overlay accuracy (30 deviation) of 50 nm has been achieved using the same modified scanning electron microscope.
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Lateral transport in GaAs/AlGaAs quantum wells

D. Araújo, G. Oelgart, J.‐D. Ganière, and F. K. Reinhart

Appl. Phys. Lett. 62, 2992 (1993); http://dx.doi.org/10.1063/1.109167 (3 pages) | Cited 8 times

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The lateral transport of excess carriers in metal organic chemical vapor deposition grown GaAs/AlxGa1−xAs(x=0.5) 20 Å thick single quantum well structures is studied by cathodoluminescence (CL) between 5 K≤T≤170 K. Impurity and native defect related transitions are found to take place around grown‐in dislocations where well thickness variations are also found. The CL intensity of free excitons and/or transitions involving impurities and native defects is measured as a function of distance from the dislocation to the point of excitation. Using a simple diffusion model, we are able to determine the hole diffusion length, L=1.5 μm, in slightly n‐doped SQW. This represents a novel method for the direct determination of the diffusion length in sufficiently defect‐free material.
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72.80.Ey III-V and II-VI semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
78.60.Hk Cathodoluminescence, ionoluminescence
78.66.Fd III-V semiconductors

Effects of Al2O3 cap on the structural and electrical properties of Au/Te/Au contacts on an n‐type GaAs substrate

X. W. Lin, A. Piotrowska, E. Kaminska, Z. Liliental‐Weber, J. Washburn, and E. Weber

Appl. Phys. Lett. 62, 2995 (1993); http://dx.doi.org/10.1063/1.109168 (3 pages) | Cited 3 times

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Au/Te/Au contacts to n‐type GaAs were prepared by sequential vapor deposition and subsequently annealed at temperatures in the range 420–480 °C. The structural and electrical characteristics of the contacts were characterized by transmission electron microscopy and current–voltage measurements. We found that the electrical behavior of the contacts depends dramatically on whether they are covered with an Al2O3 cap during annealing. While a cap‐annealed Au/Te/Au contact remains rectifying, annealing without the cap results in ohmic behavior. In conjunction with the observed structural properties, this phenomenon can be understood in terms of the doping model for ohmic contact formation.  
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
66.30.J- Diffusion of impurities

Silicon solar cell of 16.8 μm thickness and 14.7% efficiency

Jürgen H. Werner, Sabine Kolodinski, Uwe Rau, John K. Arch, and Elisabeth Bauser

Appl. Phys. Lett. 62, 2998 (1993); http://dx.doi.org/10.1063/1.109169 (3 pages) | Cited 17 times

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Liquid phase epitaxy provides a new impetus for thin film photovoltaics based on silicon; we apply this method for about 20‐μm‐thick solar cells with high efficiencies. The analysis of internal quantum efficiency measurements reveals that the open circuit voltages around 660 mV arise from an excellent electronic quality of our thin silicon films. Their effective minority carrier diffusion lengths range up to 317 μm, a value that exceeds the thickness of the layers by an order of magnitude. The conversion efficiencies exceed 14% with a record value of 14.7% for a 16.8‐μm‐thick epitaxial layer without special antireflecting coatings. The high open circuit voltages promise a possible boost of the efficiency toward 20% by applying light trapping schemes to optimize the short circuit current.
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84.60.Jt Photoelectric conversion
73.50.Pz Photoconduction and photovoltaic effects
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Light‐induced annealing of metastable defects in hydrogenated amorphous silicon

C. F. O. Graeff, R. Buhleier, and M. Stutzmann

Appl. Phys. Lett. 62, 3001 (1993); http://dx.doi.org/10.1063/1.109170 (3 pages) | Cited 27 times

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Measurements of light‐induced creation and annealing of metastable dangling bond defects in undoped hydrogenated amorphous silicon thin films are reported. A decrease of the defect density by 50% induced by continuous illumination is observed after fast defect creation by pulsed light. The kinetics of creation and recovery are discussed, as well as the implications for present models treating metastable defects in hydrogenated amorphous silicon.
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61.72.Cc Kinetics of defect formation and annealing
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.72.Yx Interaction between different crystal defects; gettering effect

Donor and acceptor concentrations in molecular beam epitaxial GaAs grown at 300 and 400 °C

D. C. Look, G. D. Robinson, J. R. Sizelove, and C. E. Stutz

Appl. Phys. Lett. 62, 3004 (1993); http://dx.doi.org/10.1063/1.109171 (3 pages) | Cited 27 times

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The first Hall‐effect measurements on molecular beam epitaxial GaAs layers grown at the low temperatures of 300 and 400 °C are reported. Two independent methods were used to determine donor ND and acceptor NA concentrations and activation energy ED0, with the following combined results: ND≂3±1×1018, NA≂1.5±1×1017 cm−3, and ED0=0.645±0.009 eV for the 300 °C layer; ND≂2±1×1017, NA≂7±3×1016 cm−3, and ED0=0.648±0.003 eV for the 400 °C layer. Thus, the deep donor is not the expected EL2, which has ED0=0.75±0.01 eV.
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71.55.Eq III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.61.Ey III-V semiconductors

Rapid thermal annealing induced order‐disorder transition in Ga0.52In0.48P/(Al0.35Ga0.65)0.5In0.5P heterostructures

Y. Hämisch, R. Steffen, A. Forchel, and P. Röntgen

Appl. Phys. Lett. 62, 3007 (1993); http://dx.doi.org/10.1063/1.109172 (3 pages) | Cited 5 times

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The thermally induced transition from the ordered to the disordered state of Ga0.52In0.48P/(Al0.35Ga0.65)In0.5P layers was investigated by means of rapid thermal annealing and photoluminescence spectroscopy. The annealing temperature and annealing time dependence of the luminescence was studied in the temperature range from 500 up to 1050 °C and for annealing times between 5 and 600 s. Within a very small temperature range of less than 40° we observe an emission energy blue shift of the GaInP luminescence band by about 100 meV. The shift occurs due to a complete disordering of the previously ordered layers without a simultaneous destruction of the heterostructure. The photoluminescence of the quaternary AlGaInP barrier was also observed and shows a simultaneous blue shift of about 90 meV due to an order‐disorder transition.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.55.Cr III-V semiconductors
68.55.-a Thin film structure and morphology

Two‐dimensional Shubnikov–de Haas oscillations in modulation‐doped CdTe/CdMnTe quantum‐well structures

S. Scholl, H. Schäfer, A. Waag, D. Hommel, K. von Schierstedt, B. Kuhn‐Heinrich, and G. Landwehr

Appl. Phys. Lett. 62, 3010 (1993); http://dx.doi.org/10.1063/1.109173 (3 pages) | Cited 17 times

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For the first time clear evidence for two‐dimensional Shubnikov–de Haas oscillations in modulation‐doped CdTe/CdMnTe quantum‐well structures is reported. The structures were grown by molecular‐beam epitaxy using ZnBr2 as a novel source material for the n‐type doping of II‐VI epitaxial layers. From an analysis of the Shubnikov–de Haas oscillations a carrier density of 9×1011 cm−2 and an effective mass of 0.1 m0 could be deduced. Due to band filling the Fermi energy in the subbands is shifted above the conduction‐band edge. This can be detected as a Stokes shift of absorption compared to photoluminescence recombination. From the Fermi energy shift the carrier concentration can be estimated, which agrees well with values determined by Hall‐effect measurements.
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71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.Ga II-VI semiconductors

Enhancement of photoluminescence quantum efficiency in semiconductor structures with reduced dimensionality

Al. L. Efros and V. N. Prigodin

Appl. Phys. Lett. 62, 3013 (1993); http://dx.doi.org/10.1063/1.109174 (3 pages) | Cited 5 times

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We have investigated photoluminescence quantum efficiency (QE) in disordered semiconductor systems. The value of QE is shown to depend strongly on the ratio of the temperature to the energy spread of localized electron states. We found that the high recombination rate of nonradiative centers (killers) could be reduced by the low mobility of carriers. The consequence is an enhancement of QE which is ever more remarkable in 1d semiconductor structures. This result can be used as an explanation for the high QE of porous Si, which is represented as an example of a disordered quasi‐one‐dimensional structure.
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78.55.Hx Other solid inorganic materials
72.20.Fr Low-field transport and mobility; piezoresistance
78.66.Jg Amorphous semiconductors; glasses
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Resonant tunneling through mixed quasibound states in a triple‐well structure

E. R. Brown, C. D. Parker, A. R. Calawa, and M. J. Manfra

Appl. Phys. Lett. 62, 3016 (1993); http://dx.doi.org/10.1063/1.109175 (3 pages) | Cited 8 times

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A triple‐well resonant‐tunneling structure made from the In0.53Ga0.47As/AlAs material system yields a broad negative differential resistance (NDR) region without the precipitous drop in current that occurs in single‐well structures. This NDR characteristic is attributed to resonant tunneling through mixed quasibound states. A diode made from this structure is used to generate a nearly constant power of 0.5 mW up to 16 GHz.
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73.40.Gk Tunneling
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Decrease in the intrinsic microwave loss of YBa2Cu3O6.95 by Zn doping

Kuan Zhang, D. A. Bonn, Ruixing Liang, D. J. Baar, and W. N. Hardy

Appl. Phys. Lett. 62, 3019 (1993); http://dx.doi.org/10.1063/1.109176 (3 pages) | Cited 25 times

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Measurements of the microwave surface resistance of single crystals of YBa2(Cu1−xZnx)3O6.95 at 3.8 and 34.8 GHz have been performed with zinc contents of x=0, 0.0015, and 0.0031. The microwave loss in the superconducting state decreases when zinc impurities are added, demonstrating that some defects are required to achieve state‐of‐the‐art surface resistance in this material.
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74.25.N- Response to electromagnetic fields
74.72.-h Cuprate superconductors

Microstructure of laser‐deposited superconducting Nd1.85Ce0.15CuO4−y films

D. Prasad Beesabathina, L. Salamanca‐Riba, S. N. Mao, X. X. Xi, and T. Venkatesan

Appl. Phys. Lett. 62, 3022 (1993); http://dx.doi.org/10.1063/1.109177 (3 pages) | Cited 12 times

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The morphology and microstructure of Nd1.85Ce0.15CuO4−y (NCCO) films grown epitaxially on (100) LaAlO3 (LAO) by pulsed laser deposition were studied by selected‐area electron diffraction and high‐resolution electron microscopy. The films were composed primarily of c‐axis oriented grains and did not contain any polytypoidic faulting. The in‐plane epitaxial relationship of the films was found to be [100]NCCO //[001]LAO. The Nd1.85Ce0.15CuO4−y‐LaAlO3 interface is sharp and free of defects. A weak peak around the (110) position of NCCO(T′) structure in x‐ray diffraction was observed. Using microdiffraction and energy‐dispersive x‐ray analysis, we confirmed that this peak corresponds to the (004) reflection of cubic Ce0.5Nd0.5O1.75.
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61.05.J- Electron diffraction and scattering
68.55.-a Thin film structure and morphology
74.72.-h Cuprate superconductors
81.15.Fg Pulsed laser ablation deposition

Superior flux pinning in in situ synthesized silver‐sheathed superconducting tape of Tl0.5Pb0.5Sr1.6Ba0.4Ca0.8Y0.2Cu2Oy

Z. F. Ren and J. H. Wang

Appl. Phys. Lett. 62, 3025 (1993); http://dx.doi.org/10.1063/1.109178 (3 pages) | Cited 8 times

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In situ synthesis has been developed for the first time to fabricate the Tl‐based silver‐sheathed superconducting tapes. Tapes of Tl0.5Pb0.5Sr1.6Ba0.4Ca0.8Y0.2Cu2Oy (Tl‐1212) made by the in situ synthesis method under optimal oxygen partial pressure were found to have transport Jc of 7000 A/cm2 in the absence of external magnetic field. In low magnetic field (<0.2 T) the Jc decreases rapidly with field due to weak links. But the Tl‐1212 tapes exhibited flux‐pinning properties superior to those of Tl‐1223 tapes when measured by SQUID at 77 K. XRD pattern of the powdered superconducting material shows it to be a single 1212 phase. Both transport measurement by the four‐probe method and magnetization measurement by SQUID also show that it is a single phase with zero resistance and onset transition temperatures of 97.5–99.0 and 101–103 K, respectively, under a measuring current of 150 mA.
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84.71.Mn Superconducting wires, fibers, and tapes
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.72.-h Cuprate superconductors
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

Phase development of Tl2Ba2CaCu2O8 thin films on LaAlO3 substrates

M. Lanham, T. W. James, M. Eddy, F. F. Lange, and D. R. Clarke

Appl. Phys. Lett. 62, 3028 (1993); http://dx.doi.org/10.1063/1.109149 (3 pages) | Cited 5 times

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The evolution of phases leading to the formation of epitaxial films of nominal composition Tl2Ba2CaCu2O8 on (100) LaAlO3 by post‐deposition annealing of amorphous precursor films has been investigated by examining interrupted heat‐treatment samples using analytical microscopy and x‐ray diffraction. The superconductor, with a composition of Tl1.8Ba2Ca0.94Cu2.6Ox, forms from a melt, which itself formed from intermediary crystalline phases during the continual loss of Tl2O. It is concluded that Tl1.8Ba2Ca0.94Cu2.6Ox, Cu2O, and Tl3Ca5Ox are in subsolidus equilibrium and that a melt phase exists between at least 780 and 860 °C under reducing conditions controlled by the Tl2O vapor.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
81.30.Dz Phase diagrams of other materials
68.55.-a Thin film structure and morphology

Enhanced transport critical current at high fields after heavy ion irradiation of textured TlBa2Ca2Cu3Oz thick films

J. E. Tkaczyk, J. A. DeLuca, P. L. Karas, P. J. Bednarczyk, D. K. Christen, C. E. Klabunde, and H. R. Kerchner

Appl. Phys. Lett. 62, 3031 (1993); http://dx.doi.org/10.1063/1.109150 (3 pages) | Cited 12 times

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Spray pyrolyzed T1(1223) films deposited on polycrystalline YSZ substrates are characterized before and after heavy ion irradiation. A factor of 2 decrease in zero field critical current is observed. However, significantly improved critical current is found at fields above 1 T, where intragranular effects dominate. The irreversibility line at 5 T is shifted by ∼20 K to higher temperatures. Scaling of the data before and after irradiation and at different temperatures is modeled by an expression which interpolates between single vortex pinning and collective creep.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Sv Critical currents
74.72.-h Cuprate superconductors

New high‐Tc cuprate (Tl1−xCrx) (Sr2−yBay)Ca2Cu3O9

Z. Y. Chen, Z. Z. Sheng, Y. Q. Tang, Y. F. Li, L. M. Wang, and D. O. Pederson

Appl. Phys. Lett. 62, 3034 (1993); http://dx.doi.org/10.1063/1.109130 (3 pages) | Cited 3 times

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A new series of 1223‐type (Tl,Cr)‐based cuprates, (Tl,Cr)(Sr,Ba)2Ca2Cu3Oz, have been successfully synthesized and identified by powder x‐ray diffraction and electron diffraction analyses. Ba partial substitution for Sr promotes the formation of (Tl,Cr)‐based 1223‐type compounds. Nominal samples, (Tl1−xCrx)‐(Sr2−yBay) Ca2Cu3Oz, with 0.15≤x≤0.50 and 0.50≤y≤1.50 are pure or nearly pure 1223 phase and exhibit Tc(ρ=0) in the range of 104–114 K. This new (Tl,Cr)‐based high‐Tc material may be of importance in practical applications.
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74.72.-h Cuprate superconductors
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

Superconductivity and microstructure of n‐type Ln1.85Ce0.15CuO4−y (Ln=Pr, Sm, Eu) produced under high‐pressure sintering

C. Q. Jin, Y. S. Yao, S. C. Liu, W. L. Zhou, and W. K. Wang

Appl. Phys. Lett. 62, 3037 (1993); http://dx.doi.org/10.1063/1.109131 (3 pages)

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Using an unconventional reduction method, high‐pressure sintering at 6.0 GPa and about 600 °C for 20 min, we have produced high‐quality n‐type Ln1.85Ce0.15CuO4−y (Ln=Pr, Sm, and Eu) superconductors from the as‐prepared materials. The samples show higher critical temperatures, higher superconducting phase fractions, and much lower resistances in the normal state than those synthesized by conventional methods. The increase of critical temperature in Eu1.85Ce0.15CuO4−y is most obvious with an onset temperature Tonc and zero‐resistance temperature Tc0 of 28.4 and 23.3 K, respectively. High‐pressure sintering seems to be effective on the modulation of the fine crystal and electronic structures of n‐type systems. In particular, metallic resistance versus temperature behaviors in normal states similar to those found in single crystals and epitaxial films are observed in Sm1.85Ce0.15CuO4−y and Eu1.85Ce0.15CuO4−y, in sharp contrast to the semiconductorlike behaviors in the conventionally prepared samples. From transmission electron microscopy studies, it is found that the compacting and regrowth of the polycrystal under high‐pressure sintering greatly improves the weak links at grain boundaries.
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74.72.-h Cuprate superconductors
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

All in situ deposition and characterization of YBa2Cu3O7−x thin films by low‐energy electron diffraction and low‐energy ion scattering spectroscopy

S. Tanaka, T. Nakamura, H. Tokuda, and M. Iiyama

Appl. Phys. Lett. 62, 3040 (1993); http://dx.doi.org/10.1063/1.109132 (3 pages) | Cited 9 times

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In an ultrahigh vacuum apparatus, c‐axis oriented YBa2Cu3O7−x (YBCO) thin films were deposited by an ozone‐assisted reactive coevaporation method and characterized by low‐energy electron diffraction (LEED) and low‐energy ion scattering spectroscopy (LEISS). A clean surface with crystal perfection within the top two monolayers was confirmed by LEED for the first time. LEISS analysis showed that this clean surface is terminated by Cu(1)‐O chains. These experiments also indicate that the oxygen pressure and the vacuum condition are one of the essential factors in keeping an outermost surface clean.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)

Electrical resistance of electron beam induced deposits from tungsten hexacarbonyl

P. C. Hoyle, M. Ogasawara, J. R. A. Cleaver, and H. Ahmed

Appl. Phys. Lett. 62, 3043 (1993); http://dx.doi.org/10.1063/1.109133 (3 pages) | Cited 15 times

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We studied the change in electrical conductivity of deposits from focused electron beam induced dissociation of W(CO)6 for different exposure conditions. Lines were deposited by scanning repeatedly to build up the same total electron dose; with different electron doses per scan, resistance differences of more than one order of magnitude resulted. The lines with lower deposited thicknesses also have lower resistances, and so cannot be explained in terms of constant resistivity and different cross‐sectional areas. A theoretical description involving an intermediate and a final product is proposed and compared to the experimental results.
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85.40.Hp Lithography, masks and pattern transfer
82.50.Kx Processes caused by X-rays or γ-rays
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Epitaxial growth and surface‐acoustic‐wave properties of LiTaO3 films grown by pulsed laser deposition

Yoshihiko Shibata, Kiyoshi Kaya, Kageyasu Akashi, Masaki Kanai, Tomoji Kawai, and Shichio Kawai

Appl. Phys. Lett. 62, 3046 (1993); http://dx.doi.org/10.1063/1.109134 (3 pages) | Cited 9 times

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Untwinned epitaxial films of LiTaO3 are deposited on (001), (110), and (012) sapphire substrates using a pulsed excimer‐laser ablation technique. Complete epitaxy in three dimensions is obtained under optimized conditions for each of the substrate orientations; (1) On (001) sapphire the (001) planes of the film are parallel to the (001) of the substrate [(001)LiTaO3 //(001)sapphire] and the [110] axis of the film is parallel to the [110] of the substrate ([110]LiTaO3//[110] sapphire); (2) (110)LiTaO3//(110)sapphire, [001]LiTaO3//[001]sapphire); (3) (012)LiTaO3//(012)sapphire, [011]LiTaO3//[011]sapphire. We have evaluated surface‐acoustic‐wave properties of these films.
Show PACS
81.15.Fg Pulsed laser ablation deposition
68.55.-a Thin film structure and morphology
77.55.-g Dielectric thin films
68.60.Bs Mechanical and acoustical properties
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