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29 Jan 1990

Volume 56, Issue 5, pp. 411-496

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Film thickness dependence of dislocation density reduction in GaAs‐on‐Si substrates

Masami Tachikawa and Masafumi Yamaguchi

Appl. Phys. Lett. 56, 484 (1990); http://dx.doi.org/10.1063/1.102773 (3 pages) | Cited 36 times

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Low dislocation density (4×105 cm−2) GaAs films on Si substrates have been obtained with a GaAs film thickness of 180 μm using vapor mixing epitaxy based on GaCl‐AsH3 (hydride) vapor phase epitaxy for the first time. Dislocation density decreases as the GaAs film thickness increases. Dislocation density is inversely proportional to film thickness in the film thickness region of <10 μm. However, in the film thickness region >50 μm (and/or of dislocation density <107 cm−2), dislocation density is exponentially proportional to the film thickness. Assuming that this dependence results from a dislocation reaction during GaAs growth, it can be interpreted that the dislocation‐dislocation coalescence reaction mainly occurs with high dislocation density crystals, and additionally, a dislocation annihilation reaction, deflection, occurs with low dislocation density crystals.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Occurrence of maximum Tc at an optimal carrier concentration in superconducting bismuth and thallium cuprates

P. Somasundaram, R. Vijayaraghavan, R. Nagarajan, Ram Seshadri, A. M. Umarji, and C. N. R. Rao

Appl. Phys. Lett. 56, 487 (1990); http://dx.doi.org/10.1063/1.103296 (3 pages) | Cited 10 times

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The superconducting transition temperatures in Bi2Ca1−xLnxSr2Cu2O8+δ, TlCa1−xLnxSr2Cu2O6+δ, and Tl0.8Ca1−xLnxBa2Cu23O6+δ (Ln=Y or rare earth) vary with composition and show a maximum at a specific value of x or δ. This observation suggests that an optimal carrier concentration is required to attain maximum Tc in such cuprates which seem to be two‐band systems.
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74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.20.Mn Nonconventional mechanisms
74.20.Rp Pairing symmetries (other than s-wave)
74.70.-b Superconducting materials other than cuprates
71.20.-b Electron density of states and band structure of crystalline solids

Molecular beam epitaxial growth of InAs on a TlBaCaCuO superconducting film

M. R. Rao, E. J. Tarsa, H. Kroemer, A. C. Gossard, E. L. Hu, P. M. Petroff, W. L. Olson, and M. M. Eddy

Appl. Phys. Lett. 56, 490 (1990); http://dx.doi.org/10.1063/1.103297 (3 pages) | Cited 8 times

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Results of growth of InAs on a superconducting TlCaBaCuO (2‐1‐2‐2) thin film are reported. The InAs was grown by molecular beam migration‐enhanced epitaxy at a substrate temperature of 250 °C. The Tc(zero) of the Tl film before and after InAs deposition was 106 and 100 K, respectively. X‐ray diffraction and reflection electron microscopy studies showed the InAs to be polycrystalline, having grains in the 300 Å size range. This is the first report of deposition of a III‐V semiconductor on superconductor, without significant degradation of Tc.
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74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Superconductivity in a Ag‐doped Bi‐Pb‐Sr‐Ca‐Cu‐O system

S. X. Dou, K.‐H. Song, H. K. Liu, C. C. Sorrell, M. H. Apperley, and N. Savvides

Appl. Phys. Lett. 56, 493 (1990); http://dx.doi.org/10.1063/1.103298 (2 pages) | Cited 16 times

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For the Bi‐Pb‐Sr‐Ca‐Cu‐O (BPSCCO) system, a consistent set of data for Tc, x‐ray diffraction, and scanning electron microscopy shows that Ag additions strongly react with BPSCCO to destabilize the 110 K superconducting phase, resulting in a strong depression in Tc and lattice parameters when samples are treated in air or pure oxygen. This is in contrast to the behavior for the Y‐Ba‐Cu‐O and Bi‐Sr‐Ca‐Cu‐O systems, which do not show such degradation. However, Ag additions show no effects on Tc and lattice parameters when samples are treated under low oxygen pressure. The formation of a low‐melting eutectic liquid with Ag2O‐PbO‐CuO solid solution affects the composition of the superconducting phase and degrades superconductivity, while the eutectic may be suppressed by reducing the oxygen partial pressure.
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74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.70.-b Superconducting materials other than cuprates

Attractor crowding in Josephson junction arrays

Kwok Yeung Tsang and Kurt Wiesenfeld

Appl. Phys. Lett. 56, 495 (1990); http://dx.doi.org/10.1063/1.102774 (2 pages) | Cited 32 times

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Large arrays of coupled nonlinear oscillators can suffer a noise sensitivity due to competition between huge numbers of coexisting states. We have found direct numerical evidence that a Josephson junction series array can exhibit attractor crowding. Thus, for the parameter values considered, no matter how small the noise level, there is a limit to the size of the array beyond which noise corrupts the in‐phase dynamical state.
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85.25.Cp Josephson devices
05.45.-a Nonlinear dynamics and chaos
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion
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