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12 Dec 1988

Volume 53, Issue 24, pp. 2359-2454

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Quantitative defect etching of GaAs on Si: Is it possible?

D. J. Stirland

Appl. Phys. Lett. 53, 2432 (1988); http://dx.doi.org/10.1063/1.100211 (3 pages) | Cited 11 times

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The Wright etch [M. W. Jenkins, J. Electrochem. Soc. 124, 757 (1977)], hitherto used to reveal defects in silicon, has been examined as a defect etchant for GaAs epitaxial layers on silicon. Various calibration techniques, including transmission electron microscopy of etched epitaxial layers, have been used to establish that etch features correspond with dislocations. Problems involved in direct comparisons of defect densities measured by different methods are discussed.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.65.-b Surface treatments

Growth and characterization of GaAs layers on Si substrates by migration‐enhanced molecular beam epitaxy

Jae‐Hoon Kim, John K. Liu, Gouri Radhakrishnan, Joseph Katz, Shiro Sakai, Shi S. Chang, and Nadia A. El‐Masry

Appl. Phys. Lett. 53, 2435 (1988); http://dx.doi.org/10.1063/1.100212 (3 pages) | Cited 11 times

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We first report on migration‐enhanced molecular beam epitaxial (MEMBE) growth and characterization of the GaAs layer on Si substrates (GaAs/Si). Excellent surface morphology GaAs layers were successfully grown on (100)Si substrates misoriented 4° toward the [110] direction. The MEMBE growth method is described, and material properties are compared with those of normal two‐step MBE‐grown or in situ annealed layers. Micrographs of cross‐section view transmission electron microscopy (TEM) and scanning surface electron microscopy (SEM) of MEMBE‐grown GaAs/Si showed dislocation densities of 1×107 cm−2, over ten times lower than those of normal two‐step MBE‐grown or in situ annealed layers. AlGaAs/GaAs double heterostructures have been successfully grown on MEMBE GaAs/Si by both metalorganic chemical vapor deposition and liquid phase epitaxy.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
66.30.J- Diffusion of impurities
68.55.-a Thin film structure and morphology

Spectroscopic studies of the influence of intentionally increased CO partial pressure on the incorporation of residual C impurities in molecular beam epitaxy GaAs

B. Lee, S. S. Bose, M. H. Kim, G. E. Stillman, and A. R. Calawa

Appl. Phys. Lett. 53, 2438 (1988); http://dx.doi.org/10.1063/1.100410 (3 pages)

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High‐purity Si‐doped molecular beam epitaxy (MBE) GaAs layers grown with and without the intentional introduction of CO gas have been characterized by Hall effect measurements, photoluminescence, and photothermal ionization spectroscopy. The results indicate that CO itself is not the source of residual C acceptor impurities in MBE GaAs samples. The observations of the correlation of residual C impurity incorporation with the residual CO gas in the MBE growth chamber suggest that the partial pressure of CO, PCO , gives a quantitative indication of background levels of hydrocarbons which are the source of C acceptors.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

NbN Josephson tunnel junctions for terahertz local oscillators

R. P. Robertazzi and R. A. Buhrman

Appl. Phys. Lett. 53, 2441 (1988); http://dx.doi.org/10.1063/1.100213 (3 pages) | Cited 4 times

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Rugged, high current density NbN1−xCx/MgO/NbN1−xCx tunnel junctions have been fabricated and tested as voltage tunable Josephson junction terahertz oscillators. The emitted radiation from these junctions is detected on chip by a second junction which is capacitively coupled to the first. For oscillator junctions with a critical current density of Jc∼3.5×104 A/cm2 we find that the junction oscillates with a voltage amplitude of ∼1.5 mV. The detected rf voltage level remains essentially constant from 300 GHz to above 1 THz. The oscillator junction produces 0.5 μW of terahertz radiation of which, due to impedance mismatch, 0.01 μW is coupled into the detector junction.
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85.25.Cp Josephson devices
74.50.+r Tunneling phenomena; Josephson effects
84.30.Ng Oscillators, pulse generators, and function generators
74.78.-w Superconducting films and low-dimensional structures

Pinning mechanism in a continuous ultrafine Nb3Al multifilamentary superconductor

T. Takeuchi, Y. Iijima, M. Kosuge, K. Inoue, K. Watanabe, and K. Noto

Appl. Phys. Lett. 53, 2444 (1988); http://dx.doi.org/10.1063/1.100523 (3 pages) | Cited 4 times

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For Nb3Al multifilamentary superconductors fabricated by a newly developed composite process using continuous ultrafine Al‐based alloy cores and pure Nb matrix, Jc properties have been investigated in detail in regard to the size and morphology of the Al core. A significant enhancement in pinning force caused by reducing the Al core size and an anisotropy in Jc observed in a rolled tape have indicated that the Nb3Al‐matrix (or core) interface acts as a dominant pinning center of fluxoids.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)

Topography and local modification of the HoBa2Cu3O7−x(001) surface using scanning tunneling microscopy

H. Heinzelmann, D. Anselmetti, R. Wiesendanger, H.‐J. Güntherodt, E. Kaldis, and A. Wisard

Appl. Phys. Lett. 53, 2447 (1988); http://dx.doi.org/10.1063/1.100524 (3 pages) | Cited 13 times

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The topography of the (001) surface of a high Tc superconducting HoBa2Cu3O7−x single crystal was investigated in air using scanning tunneling microscopy. We found large, flat terraces separated by growth steps. The heights of these steps correspond to multiples of the c‐axis lattice constant of 11.7 Å of the perovskite structure. These steps have been verified by atomic force microscopy. On a smaller scale the flat terraces showed some fine structure with a corrugation height of 4 to 5 Å and a lateral extent of several nanometers. In addition, we succeeded in creating nanometer‐sized structures by increasing the sample bias voltage and tunneling current.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination
74.70.-b Superconducting materials other than cuprates
81.40.-z Treatment of materials and its effects on microstructure, nanostructure, and properties

Growth of superconducting Bi2Sr2CaCu2O8+x films on alumina, silicon, and fused quartz

L. S. Hung, J. A. Agostinelli, G. R. Paz‐Pujalt, and J. M. Mir

Appl. Phys. Lett. 53, 2450 (1988); http://dx.doi.org/10.1063/1.100525 (3 pages) | Cited 16 times

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Interactions between superconducting Bi2Sr2CaCu2O8+x films and substrates were investigated by ion backscattering, x‐ray diffraction, and four‐point probe resistivity measurements. During annealing at temperatures above‐ 800 °C, Bi2Sr2CaCu2 oxide films rapidly reacted with alumina, Si, Si covered with SiO2, and quartz, resulting in catastrophic failure. Zr‐based barrier layers were used to minimize film‐substrate interactions. When a single ZrO2 layer was interposed between the superconducting oxide film and the underlying substrate, the Bi2Sr2CaCu2 oxide films showed a large‐grained polycrystalline microstructure and exhibited the orthorhombic structure. Films on sapphire showed transitions to the superconducting state beginning near 100 K with zero resistance achieved at 70 K. Films on Si and thermally grown SiO2 showed a similar drop in resistance around 95 K, whereas the transition was broad and the zero resistance state was not reached. For films on quartz, high thermal stress caused cracking of the superconducting oxide film. Best results were achieved using a barrier composed of a Zr‐Si‐O mixed layer underneath ZrO2. In this case, the films grown on Si and quartz were uniform and showed the onset to superconductivity at 95 K, attaining zero resistance at 70 K.
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74.78.-w Superconducting films and low-dimensional structures
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
74.70.-b Superconducting materials other than cuprates
68.35.Fx Diffusion; interface formation

Kerr rotation enhancement in metallic bilayer thin films for magneto‐optical recording

W. Reim and D. Weller

Appl. Phys. Lett. 53, 2453 (1988); http://dx.doi.org/10.1063/1.100526 (2 pages) | Cited 25 times

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The enhancement of the magneto‐optical Kerr effect via metallic bilayer structures is demonstrated for magneto‐optic square loop materials on top of optically thick silver and copper reflectors, respectively. We show that in general an enhancement of the polar Kerr rotation angle θK occurs at photon energies where the optical constants n and k of the reflector have low values. The enhancement factor depends on the thickness of the magnetic layer and on the relative magnitude of the optical constants of both layers. The reflectivity of these bilayer structures is only slightly reduced compared to the bulk magneto‐optical medium.
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78.66.Bz Metals and metallic alloys
78.20.Ls Magneto-optical effects
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