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18 Mar 1991

Volume 58, Issue 11, pp. 1119-1219

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Persistent photoconductivity in low‐energy argon ion‐bombarded semi‐insulating GaAs

A. Vaseashta and L. C. Burton

Appl. Phys. Lett. 58, 1193 (1991); http://dx.doi.org/10.1063/1.104362 (3 pages) | Cited 3 times

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Time‐dependent phototransport measurements are presented for low‐energy argon ion‐bombarded semi‐insulating liquid‐encapsulated Czochralski GaAs. Distinct changes caused by ion beam etching were persistent photoconductivity and an increase in photosensitivity. The time dependence of photoconductivity indicated direct participation of the EL2 center. An ion beam induced and optically generated metastable defect state is suggested in the near‐surface disordered region to describe the observed phenomena.
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72.40.+w Photoconduction and photovoltaic effects
61.80.Jh Ion radiation effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.25.+i Surface conductivity and carrier phenomena

Crystallization of amorphous silicon by reconstructive transformation utilizing gold

J. Stoemenos, J. McIntosh, N. A. Economou, Y. K. Bhatnagar, P. A. Coxon, A. J. Lowe, and M. G. Clark

Appl. Phys. Lett. 58, 1196 (1991); http://dx.doi.org/10.1063/1.104363 (3 pages) | Cited 9 times

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A gold layer one order of magnitude thinner than the thickness of an amorphous silicon layer in intimate contact leads to the dissolution of the amorphous silicon into the liquid and the subsequent precipitation of crystalline Si as the liquid phase propagates into the amorphous phase at above eutectic temperatures. The crystalline Si precipitate has grain sizes of the order of 6 μm. The Si/Au liquid is very sensitive to constitutional supercooling and subsequent crystallization.
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68.35.Rh Phase transitions and critical phenomena
81.30.Fb Solidification
81.30.Mh Solid-phase precipitation

Native oxide stabilization of AlAs‐GaAs heterostructures

A. R. Sugg, N. Holonyak, J. E. Baker, F. A. Kish, and J. M. Dallesasse

Appl. Phys. Lett. 58, 1199 (1991); http://dx.doi.org/10.1063/1.105213 (3 pages) | Cited 46 times

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Data are presented on the stabilization of AlAs‐GaAs heterostructures against atmospheric (destructive) hydrolysis using the native oxide that can be formed (N2+H2O, 400 °C, 3 h) on the AlAs layer. The ∼0.1‐μm‐thick native oxide formed from the AlAs layer is shown to be stable with aging (∼100 days), while unoxidized samples degrade through the AlAs (0.1 μm) down into the GaAs as deep as ∼1 μm. Relative to oxides formed (∼25 °C) on AlAs (or AlxGa1−xAs, x ≳ 0.7) under atmospheric conditions (hydrolysis), oxides formed (via N2 +H2O) at higher temperatures (≳400 °C) are much more stable and seal the underlying crystal (e.g., GaAs).
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81.65.-b Surface treatments

Critical current density enhancement in YBa2Cu3O6.8 films on buffered metallic substrates

E. Narumi, L. W. Song, F. Yang, S. Patel, Y. H. Kao, and D. T. Shaw

Appl. Phys. Lett. 58, 1202 (1991); http://dx.doi.org/10.1063/1.104364 (3 pages) | Cited 23 times

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A transition buffer, consisting of subbuffers grown at different temperatures, was used to enhance the crystallinity and the transport properties of YBa2Cu3O6.8 (YBCO) films on metallic substrates. Films were fabricated using in situ laser deposition and were strongly c‐axis oriented. Critical temperature of 87 K and critical current density of 3×104 A/cm2 at 77 K were obtained for a 0.5‐μm‐thick YBCO film with a 0.2 μm transition yttrium‐ stabilized ZrO2 buffer layer. Also, the magnetic field dependence of Jc could be enhanced by using Pt‐coated metallic substrates.
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74.25.Sv Critical currents
74.78.-w Superconducting films and low-dimensional structures

Magnetic field dependence of the critical current anisotropy in normal metal‐YBa2Cu3O7−δ thin‐film bilayers

R. H. Ono, L. F. Goodrich, J. A. Beall, M. E. Johansson, and C. D. Reintsema

Appl. Phys. Lett. 58, 1205 (1991); http://dx.doi.org/10.1063/1.104365 (3 pages) | Cited 2 times

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We have measured the transport critical current density (Jc) in epitaxial quality films of YBa2Cu3O7−δ some of which were covered by thin (10 nm) Ag films. The films, both with and without Ag, had Jc values greater than 106 A/cm2 in liquid nitrogen. The effect of the Ag was to greatly reduce the dependence of Jc on external magnetic fields in the case where the field was oriented in the plane of the film, that is, perpendicular to the c axis. It is unlikely that the effect is simply due to altered surface pinning, although qualitative agreement with critical state models is observed.
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74.25.Sv Critical currents
74.78.-w Superconducting films and low-dimensional structures
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)

Modeling superconductor degradation using magnetic levitation

M. A. Sriram, Laura Ponce, and L. E. Murr

Appl. Phys. Lett. 58, 1208 (1991); http://dx.doi.org/10.1063/1.104366 (3 pages)

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Corrosion of YBa2Cu3O7−x pellets has been studied using magnetic levitation. Pellets compressed at green compaction pressures of 120–200 MPa were exposed to water and air and the levitation heights were measured over a period of more than a month. A model based on diffusion as a rate‐controlling step has been proposed. Levitation height normalized with respect to the initial levitation height was used as the modeling parameter. The experiments indicate that the normalized levitation height decreased with time up to a certain level called the saturation leviation, beyond which there is no change in the levitation height. Samples in air degraded faster than samples in water. The initial period of degradation before saturation fits the proposed model well and therefore appears to be diffusion controlled. The saturation levitation shows a dependence on the green compaction pressure. It has been proposed that corrosion (degrading reactions) is due to open porosities which are closed by the reaction products, thus causing a saturation in the levitation height dependent on the porosities.
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74.25.Ha Magnetic properties including vortex structures and related phenomena
74.70.-b Superconducting materials other than cuprates
07.55.Db Generation of magnetic fields; magnets
85.70.-w Magnetic devices

Laser deposition of YBa2Cu3O7−δ films using a pulsed oxygen source

A. Gupta and B. W. Hussey

Appl. Phys. Lett. 58, 1211 (1991); http://dx.doi.org/10.1063/1.104367 (3 pages) | Cited 37 times

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Thin films of YBa2Cu3O7−δ (YBCO) have been grown by pulsed laser deposition in a low‐pressure background (10−4–10−3 Torr) by using a pulsed, high intensity jet of O2 or N2O for oxidation. The oxygen source is provided by a pulsed molecular beam valve, and the opening of the valve and the triggering of the laser are synchronized with appropriate delay so that the supersonic gas jet and the ablated fragments arrive at the substrate at the same time. This provides the necessary oxygen to form the YBCO phase while maintaining a low oxygen background. The YBCO phase is not formed if the oxygen pulse is provided either before or much after the arrival of the ablation fragments at the substrate. The ability to grow superconducting films at low background pressures should allow usage of in situ analysis techniques, such as reflection high‐energy electron diffraction, during pulsed laser deposition.
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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
74.78.-w Superconducting films and low-dimensional structures

Elementary formula for the magneto‐optic Kerr effect from model superlattices

J. Zak, E. R. Moog, C. Liu, and S. D. Bader

Appl. Phys. Lett. 58, 1214 (1991); http://dx.doi.org/10.1063/1.104368 (3 pages) | Cited 5 times

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An elementary formula is derived for the magneto‐optic Kerr effect from model superlattices. An exact result is obtained for the case of equal refractive indices for the two constituents of the superlattice. Co/Pt is used as an example of such superlattices for wavelengths in the vicinity of 2 eV. First‐order corrections in the difference of the refractive indices are derived which are suitable for treating a variety of materials.
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78.20.Ls Magneto-optical effects
78.20.Bh Theory, models, and numerical simulation
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Some photoeffect roles in rapid isothermal processing

R. Singh, S. Sinha, R. P. S. Thakur, and P. Chou

Appl. Phys. Lett. 58, 1217 (1991); http://dx.doi.org/10.1063/1.104369 (3 pages) | Cited 42 times

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When compared to furnace processing, for identical and lower substrate temperatures, more photons are available in the visible and ultraviolet regions for rapid isothermal processing (RIP) based on incoherent radiation as the energy source. In this letter, we provide experimental evidence for photoeffects in RIP for a wide variety of materials. As compared to furnace processed samples, rapid isothermal annealed phosphosilicate glass films on Si substrate show a higher value of refractive index, a lower flatband charge density, and a lower thermal stress. High‐temperature superconducting thin films on Y‐Ba‐Cu‐O deposited by RIP assisted metalorganic chemical vapor deposition on yttrium stabilized zirconia substrate show a larger grain size, a higher value of the transition temperature than their furnace counterpart. The microscopic understanding of a particular deposition or annealing process is necessary to take full advantage of photoeffects in RIP.
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78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
81.40.Tv Optical and dielectric properties related to treatment conditions
78.66.-w Optical properties of specific thin films
78.66.Jg Amorphous semiconductors; glasses
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