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25 Feb 1991

Volume 58, Issue 8, pp. 787-873

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Signature of the gallium‐oxygen‐gallium defect in GaAs by deep level transient spectroscopy measurements

S. T. Neild, M. Skowronski, and J. Lagowski

Appl. Phys. Lett. 58, 859 (1991); http://dx.doi.org/10.1063/1.104513 (3 pages) | Cited 33 times

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Experimental results of deep level transient spectroscopy (DLTS) and Fourier transform infrared spectroscopy (FTIR) on oxygen‐doped GaAs crystals are presented. A positive identification of the DLTS signature of the Ga‐O‐Ga defect (tentatively identified as an oxygen‐arsenic vacancy complex) is made through correlation with FTIR measurements. The energy level for the two‐electron state of the defect is found to be located at 0.55 eV below the conduction band, and direct proof is given that this center is actually a negative U center. A calibration factor for local vibrational mode absorption is calculated to be 8×1016 cm−1.
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71.55.Eq III-V semiconductors
78.30.-j Infrared and Raman spectra
78.40.Fy Semiconductors
78.47.-p Spectroscopy of solid state dynamics

Improvement of GaAs crystal quality grown on Si by metalorganic chemical vapor deposition through two‐dimensional‐like nucleation with an in situ H2/AsH3 plasma cleaning at 450 °C

Euijoon Yoon and Rafael Reif

Appl. Phys. Lett. 58, 862 (1991); http://dx.doi.org/10.1063/1.104514 (3 pages)

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We demonstrate that in situ Si cleaning techniques prior to low‐temperature GaAs buffer layer growth affect the morphology of the GaAs buffer layer in the early stages of growth and the crystal quality of 3‐μm‐thick GaAs grown epitaxially afterward on the buffer layer at 650 °C. Both thermal cleaning and hydrogen/arsine plasma cleaning at 650 °C result in a bimodal distribution of GaAs nuclei on Si, although the number of larger nuclei with {111} facets decreases with the plasma cleaning. No such larger islands are observed with hydrogen/arsine plasma cleaning at 450 °C, and this makes possible a two‐dimensional‐like nucleation of the buffer layer. This two‐dimensional‐like nucleation of the buffer layer, in contrast to the bimodal nucleation behavior observed in other cleaning conditions, leads to a significant improvement in GaAs crystal quality with a reduction of full width at half maximum from 755 to 306 arcsec as measured by double‐crystal diffractometry.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.65.-b Surface treatments

In situ extended x‐ray absorption fine structure spectroscopy of thin‐film nickel hydroxide electrodes

T. W. Capehart, D. A. Corrigan, R. S. Conell, K. I. Pandya, and R. W. Hoffman

Appl. Phys. Lett. 58, 865 (1991); http://dx.doi.org/10.1063/1.104489 (3 pages) | Cited 19 times

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A convenient in situ electrochemical cell has been developed which permits x‐ray absorption measurements on thin‐film electrodes under electrochemical polarization. Extended x‐ray absorption fine structure spectra from highly disordered α‐Ni(OH)2 films, before and after polarization, provided quantitative results on the lattice contraction accompanying oxidation. Upon oxidation of α‐Ni(OH)2, the Ni‐O distance contracted from 2.05 to 1.86 Å, and the Ni‐Ni distance contracted from 3.09 to 2.82 Å. The observed 10% contraction in the brucite plane is consistent with the 3.67 nickel valence in a K(NiO2)3 phase. The present technique extends x‐ray absorption spectroscopy to the study of a variety of unstable materials not amenable to ex situ techniques.
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78.70.Dm X-ray absorption spectra
82.45.-h Electrochemistry and electrophoresis

Critical currents and magnetization in c‐axis textured Bi‐Pb‐Sr‐Ca‐Cu‐O superconductors

S. Jin, R. B. van Dover, T. H. Tiefel, J. E. Graebner, and N. D. Spencer

Appl. Phys. Lett. 58, 868 (1991); http://dx.doi.org/10.1063/1.104490 (3 pages) | Cited 35 times

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Transport critical currents and magnetization behavior in c‐axis textured Bi‐Pb‐Sr‐Ca‐Cu‐O superconductor ribbons have been studied. The highly oriented layer structure was achieved by a combination processing of spray coating on silver foil, cold rolling, and partial melting. Transport Jc values as high as 2.3×105 A/cm2 at 4.2 K, H=8 T (H⊥ab) have been obtained. The high Jc at H≥5 T is maintained to temperatures near 20 K but it vanishes completely at or above ∼30 K, thus showing the limitation in useful, high‐field operating temperatures for the Bi‐system superconductors. A comparison of Jc (transport) and Jc (magnetization) indicates that the size scale of the circulating supercurrent loop in the Bean model nearly corresponds to the whole sample dimension rather than the orders‐of‐magnitude‐smaller grain size. This demonstrates that the a‐b grain boundaries in the melt‐processed ribbons are not weakly coupled. The time decay of magnetization has also been studied.
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74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Ha Magnetic properties including vortex structures and related phenomena

Dependence of crystalline orientation on film thickness in laser‐ablated YBa2Cu3O7−δ on LaAlO3

A. H. Carim, S. N. Basu, and R. E. Muenchausen

Appl. Phys. Lett. 58, 871 (1991); http://dx.doi.org/10.1063/1.104491 (3 pages) | Cited 33 times

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The microstructure of YBa2Cu3O7−δ thin films deposited on (001)LaAlO3 substrates by a laser ablation process has been investigated by scanning electron microscopy, x‐ray diffraction, and cross‐sectional transmission electron microscopy. Adjacent to the substrate, the film is entirely oriented with the c‐axis perpendicular to the surface. At a thickness of about 0.4 μm, the occurrence of 90° boundaries brings about a transition to grains with their c‐axes parallel to the surface (aligned along the [100] and [010] directions of the pseudocubic LaAlO3 substrate). This transition is discussed in terms of the crystal growth anisotropy and the retained strain that may precipitate the transition.
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74.78.-w Superconducting films and low-dimensional structures
68.55.-a Thin film structure and morphology
81.15.Rs Spray coating techniques
74.70.-b Superconducting materials other than cuprates
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