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11 Jun 1990

Volume 56, Issue 24, pp. 2367-2473

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Epitaxial tendencies of ReSi2 on (001) silicon

John E. Mahan, Kent M. Geib, Gary Y. Robinson, Robert G. Long, Yan Xinghua, Gang Bai, Marc‐A. Nicolet, and Menachem Nathan

Appl. Phys. Lett. 56, 2439 (1990); http://dx.doi.org/10.1063/1.103251 (3 pages) | Cited 11 times

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ReSi2 thin films were grown on (001) silicon wafers by vacuum evaporation of rhenium onto hot substrates in ultrahigh vacuum. The preferred epitaxial relationship was found to be ReSi2 (100)/Si(001) with ReSi2 [010]∥Si〈110〉. The lattice matching consists of a common unit mesh of 120 Å2 area, and a mismatch of 1.8%. Transmission electron microscopy revealed the existence of rotation twins corresponding to two distinct but equivalent azimuthal orientations of the common unit mesh. Although the lateral dimension of the twins is on the order of 100 Å, MeV He+ backscattering spectrometry revealed a minimum channeling yield of 2% for a ∼1500‐Å‐thick film grown at 650 °C. There is a very high degree of alignment between the ReSi2 (100) and the Si(001) planes.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Low surface recombination velocity and contact resistance using p+/p carbon‐doped GaAs structures

T. J. de Lyon, J. A. Kash, S. Tiwari, J. M. Woodall, D. Yan, and F. H. Pollak

Appl. Phys. Lett. 56, 2442 (1990); http://dx.doi.org/10.1063/1.102903 (3 pages) | Cited 6 times

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A reduction of the GaAs surface recombination velocity due to a heavily carbon‐doped GaAs overlayer is reported. Metalorganic molecular beam epitaxy using trimethylgallium, triethylgallium, and elemental arsenic sources has been used to grow an epitaxial structure consisting of 1000 nm of p=1×1017 cm−3 capped with 10 nm of p=1×1020 cm−3 GaAs. Time‐resolved photoluminescence (PL) and PL excitation spectroscopy showed this p+/p structure to have a 3.2 ns carrier lifetime and strong band‐edge PL emission, whose intensity was nearly constant over an excitation photon energy range of 1.5–3.3 eV. The same wafer with the p+ cap etched off exhibited a much shorter carrier lifetime and PL intensity that decreased exponentially with increasing photon energy, which is indicative of carrier losses to surface recombination. The specific contact resistivity of nonalloyed ohmic contacts to these heavily doped layers was observed to be in the mid 10−7 Ω cm2 range, independent of measurement temperature from 77 to 340 K, suggesting a tunneling contact due to the narrow surface depletion layer.
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73.40.Cg Contact resistance, contact potential
73.40.Ns Metal-nonmetal contacts
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Ey III-V and II-VI semiconductors

Enhanced strain relaxation in Si/GexSi1−x/Si heterostructures via point‐defect concentrations introduced by ion implantation

R. Hull, J. C. Bean, J. M. Bonar, G. S. Higashi, K. T. Short, H. Temkin, and A. E. White

Appl. Phys. Lett. 56, 2445 (1990); http://dx.doi.org/10.1063/1.102904 (3 pages) | Cited 41 times

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It is shown that strain relaxation during annealing of Si/GexSi1−x/Si heterostructures is significantly enhanced if the strained GexSi1−x layers are implanted with p (B) or n (As) type dopants below the amorphization dose. Comparison of strain relaxation during in situ annealing studies in a transmission electron microscope between unimplanted and implanted structures reveals that the latter show residual strains substantialy below those for unimplanted structures. We propose that this enhanced relaxation is caused by increased dislocation nucleation probabilities due to the high point‐defect concentrations arising from implantation.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Deposition‐induced defect profiles in amorphous hydrogenated silicon

N. Hata, S. Wagner, P. Roca i Cabarrocas, and M. Favre

Appl. Phys. Lett. 56, 2448 (1990); http://dx.doi.org/10.1063/1.102905 (3 pages) | Cited 12 times

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The thickness dependence of the subgap optical absorption in plasma‐deposited hydrogenated amorphous silicon is carefully studied by photothermal deflection spectroscopy. The deep‐level defect concentration decays from the top surface into the bulk where it approaches the thermal equilibrium defect density. This defect profile is interpreted in terms of the annealing, during growth, of growth‐induced surface defects. It is also shown that this defect profile is compatible with the known growth‐temperature dependence of the defect density in amorphous silicon.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
71.23.-k Electronic structure of disordered solids
78.30.-j Infrared and Raman spectra
78.40.Fy Semiconductors
72.80.Ng Disordered solids

Effect of sputtering current on the growth of Y‐Ba‐Cu‐O films

R. J. Lin

Appl. Phys. Lett. 56, 2451 (1990); http://dx.doi.org/10.1063/1.103252 (3 pages)

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Y‐Ba‐Cu‐O (YBCO) films were grown on (100)MgO and (100)Si substrates by the high‐pressure dc diode sputtering process. The target was a Y1Ba2Cu3Ox compound, made by a solid‐state reaction. The sputtering gas was Ar‐50% O2 and the total pressure was 1.5 Torr. As‐deposited superconducting YBCO films can be prepared at low substrate temperatures (420 °C) with a high discharge current. The phases of the as‐deposited films strongly relate to the discharge current and substrate temperature. The high concentration of active species (excited atoms and ions) in the plasma during deposition is the main factor that permits superconducting YBCO films to be formed at such low substrate temperatures.
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74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates
81.15.Cd Deposition by sputtering

In situ preparation of the Gd‐Ba‐Cu‐O superconducting thin films on (100) LaAlO3 by sputtering

H. C. Li, H. R. Yi, R. L. Wang, Y. Chen, B. Yin, X. S. Ron, and L. Li

Appl. Phys. Lett. 56, 2454 (1990); http://dx.doi.org/10.1063/1.103253 (2 pages) | Cited 12 times

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High‐temperature superconductor GdBa2Cu3O7 thin films were grown in situ on LaAlO3 single‐crystal substrates by dc magnetron sputtering using a single planar target. 93% samples had a zero resistance transition temperature Tc0 more than 90 K and a transition width less than 1 K. The best films had a Tc0 of 92.5 K, a transition width of 0.57 K, and a critical current density of 3.6×106 A/cm2 at 77 K. The reproducibility is very good. X‐ray diffraction analysis showed c axis normal to the film’s surface.
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81.15.Cd Deposition by sputtering
74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates
74.25.Sv Critical currents

Strongly enhanced flux pinning by high‐energy proton irradiation of a Tl2Ca2Ba2Cu3Oy single crystal

E. L. Venturini, J. C. Barbour, D. S. Ginley, R. J. Baughman, and B. Morosin

Appl. Phys. Lett. 56, 2456 (1990); http://dx.doi.org/10.1063/1.103254 (3 pages) | Cited 18 times

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Flux creep data are reported which clearly demonstrate a dramatic enhancement in the pinning potential for magnetic vortices (fluxoids) in a Tl2Ca2Ba2Cu3Oy single crystal upon irradiation with 4.5 MeV protons. The creep rate is markedly reduced between 5 and 80 K, and the effective pinning potential is quadrupled from ≊100 to ≊400 meV at 20 K in a field of 50 mT. This stronger pinning enhances the magnetization hysteresis and hence the inferred low‐field critical current density by a factor of 5 at 40 K.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.N- Response to electromagnetic fields
74.70.-b Superconducting materials other than cuprates
74.25.Sv Critical currents

Recovery of 90 K superconductivity in transition‐metal‐doped Y‐Ba‐Cu‐O

G. W. Kammlott, T. H. Tiefel, and S. Jin

Appl. Phys. Lett. 56, 2459 (1990); http://dx.doi.org/10.1063/1.103255 (3 pages) | Cited 31 times

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Most of the transition metal elements incorporated into the lattice of YBa2Cu3O7−δ are known to severely suppress the superconducting transition temperature. In this work, we show that an essentially complete recovery of the 90 K superconductivity can be achieved by partial melt processing of the material doped with Zr, Ta, Ti, Pt, Rh, and Re, which is attributed to second phase particles draining the dopant elements away from the matrix. Such a full recovery of Tc is not obtained in the case of Nb, V, Ni, Fe, Co, Pd, and Ru. The results are of technological interest in view of the need for nonpoisonous, high melting point substrate, clad or core materials desirable for melt processing of Y‐Ba‐Cu‐O.
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74.70.-b Superconducting materials other than cuprates
74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
64.75.-g Phase equilibria

Neutron‐induced microwave loss in ceramic YBa2Cu3O7−δ

D. W. Cooke, M. S. Jahan, R. D. Brown, K. C. Ott, E. R. Gray, J. L. Smith, J. O. Willis, B. L. Bennett, M. A. Maez, E. J. Peterson, W. L. Hults, J. Y. Coulter, A. M. Portis, H. Piel, N. Klein, et al.

Appl. Phys. Lett. 56, 2462 (1990); http://dx.doi.org/10.1063/1.103256 (3 pages) | Cited 2 times

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An increase by over three orders of magnitude from 0.58 mΩ to 1.17 Ω was observed at 4.0 K in the 3 GHz microwave surface resistance of ceramic YBa2Cu3O7−δ following exposure to neutrons. The transport resistivity of an unirradiated pellet was linear in temperature down to Tc with a room‐temperature value of 2.13 mΩ cm and a resistivity extrapolated to 4.0 K of 0.53 mΩ cm. Following irradiation, the resistivity rose with decreasing temperature from a room‐temperature value of 1.5 Ω cm to a maximum at around 45 K with little change evident at Tc . These results, in conjunction with eddy current, susceptibility, iodometric titration, and thermally stimulated luminescence measurements on irradiated and unirradiated samples, collectively suggest that the effect of neutron irradiation has been to decrease intergranular coupling without the development of an insulating phase.
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74.70.-b Superconducting materials other than cuprates
74.25.N- Response to electromagnetic fields
74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
61.80.Hg Neutron radiation effects

Sharp angular sensitivity of pinning due to twin boundaries in Ba2YCu3O7

E. M. Gyorgy, R. B. van Dover, L. F. Schneemeyer, A. E. White, H. M. O’Bryan, R. J. Felder, J. V. Waszczak, W. W. Rhodes, and F. Hellman

Appl. Phys. Lett. 56, 2465 (1990); http://dx.doi.org/10.1063/1.103257 (3 pages) | Cited 56 times

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We have measured the pinning force due to twin boundaries by measuring the magnetic torque produced when a field is applied perpendicular to the c axis and rotated with respect to the ab axes. At 76 K, the torque increases roughly fourfold, when the field is within 2° of the parallel to the twin boundaries. This peak is absent at 27 K. Irradiation with 5×1016 cm−2 3.5 MeV protons increases the overall critical current and eliminates the peaks observed at 76 K.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Sv Critical currents
74.70.-b Superconducting materials other than cuprates
74.78.-w Superconducting films and low-dimensional structures

Correlations between deposition parameters and structural and electrical properties of YBa2Cu3O7−δ thin films grown in situ by sequential ion beam sputtering

J. A. Kittl, C. W. Nieh, D. S. Lee, and W. L. Johnson

Appl. Phys. Lett. 56, 2468 (1990); http://dx.doi.org/10.1063/1.103258 (3 pages) | Cited 13 times

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We have studied the correlations between deposition parameters and structural and electrical properties of YBa2Cu3O7−δ thin films grown in situ by sequential ion beam sputtering. Epitaxial, c‐axis oriented YBa2Cu3O7−δ films were grown both on (100) SrTiO3 and on (100) MgO substrates following the stacking sequence of the ‘‘123’’ compound, with deposited layer thicknesses nominally equal to 1 monolayer. The c‐axis lattice parameters obtained were larger than the corresponding lattice parameter in bulk samples, even after low‐temperature anneals in O2. The transition temperatures were found to decrease with the enlargement of the c‐axis lattice parameter. A clear correlation between growth temperature and the value of the c‐axis lattice parameter was observed. The c‐axis lattice parameter and the x‐ray linewidth of Bragg reflections with the G vector along the c‐axis were also found to be correlated. This suggests a relationship between the c‐axis lattice parameter and the structural coherence of the epitaxial films.
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74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates
81.15.Cd Deposition by sputtering
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Electromagnetic shock‐wave generation in a lumped element delay line containing nonlinear ferroelectric capacitors

C. R. Wilson, M. M. Turner, and P. W. Smith

Appl. Phys. Lett. 56, 2471 (1990); http://dx.doi.org/10.1063/1.102907 (3 pages) | Cited 9 times

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High‐voltage waveforms with rise times of 50 ns were produced by electromagnetic shock‐wave generation in a uniform, lumped element delay line constructed with nonlinear, ferroelectric capacitors. A close correlation was found between the experimental voltage waveforms observed at different positions along the delay line and those predicted by a numerical computer code.
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85.30.-z Semiconductor devices
43.38.Ar Transducing principles, materials, and structures: general
43.38.Dv Electromagnetic and electrodynamic transducers
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