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25 Dec 1989

Volume 55, Issue 26, pp. 2689-2791

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Chemical vapor deposition of CoGa and PtGa2 thin films from mixed‐metalorganometallic compounds

Yea‐Jer Chen, Herbert D. Kaesz, Young Kwan Kim, Hans‐Joachim Müller, R. Stanley Williams, and Ziling Xue

Appl. Phys. Lett. 55, 2760 (1989); http://dx.doi.org/10.1063/1.102370 (3 pages) | Cited 21 times

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A new process for deposition of thin metal films from organometallic precursors of limited volatility has been demonstrated. Short path vapor transport of the complexes dichloro(tetracarbonylcobalt)gallium(III) tetrahydrofuranate, (CO)4CoGaCl2(THF), or platinum(bis‐dimethylglyoximato)(bis‐dimethylgallium), Pt{(N2C2(CH3)2O2)(GaMe2)}2, each under a stream of hydrogen, leads to the films of the intermetallic compounds CoGa and PtGa2, respectively, on substrates such as Si (100) wafer or a glass slide at 500 °C. The compounds were identified and characterized by x‐ray diffraction, Auger electron and x‐ray photoelectron spectroscopies. The films are crystalline and highly reflective. The CoGa film is single phased; the PtGa2 film shows a minor constituent of Pt2Ga3.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology
78.66.Bz Metals and metallic alloys

Model for diffusion and trapping of hydrogen in crystalline silicon

J. P. Kalejs and S. Rajendran

Appl. Phys. Lett. 55, 2763 (1989); http://dx.doi.org/10.1063/1.101947 (3 pages) | Cited 14 times

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A simplified analysis is presented to describe diffusion and trapping of atomic hydrogen in crystalline silicon. Predictions of the rate of advancement of the trapped hydrogen front as a function of process and material variables are obtained from a numerical solution of the transport equations. We demonstrate that the solutions are compatible with data on boron passivation at 150 °C only when the diffusivities obtained by extrapolation from the high‐temperature results of Van Wieringen and Warmoltz [Physica 22, 849 (1956)] are used to represent atomic hydrogen diffusion in the absence of trapping.
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66.30.Dn Theory of diffusion and ionic conduction in solids
81.40.Rs Electrical and magnetic properties related to treatment conditions
66.30.J- Diffusion of impurities

Magnetic flux commensurability in coupled quantum dots

K. Ismail, T. P. Smith, W. T. Masselink, and Henry I. Smith

Appl. Phys. Lett. 55, 2766 (1989); http://dx.doi.org/10.1063/1.101948 (3 pages) | Cited 23 times

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We have studied the transition from isolated to coupled quantum dots in a lateral surface‐superlattice structure in the presence of a perpendicular magnetic field. The coupling between the dots can be tuned by changing the bias of the grid gate. Our magnetocapacitance measurements reveal three distinct regimes: isolated quantum dots where collective effects are not observed, a tight‐binding regime where the measurement results are sensitive to the rationality of flux quanta per unit cell, and a superlattice regime where commensurability effects between the magnetic orbits and the superlattice periodicity are observed.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Atomic layer epitaxy of device quality GaAs

E. Colas, R. Bhat, B. J. Skromme, and G. C. Nihous

Appl. Phys. Lett. 55, 2769 (1989); http://dx.doi.org/10.1063/1.101949 (3 pages) | Cited 12 times

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Device quality GaAs was grown in a conventional organometallic chemical vapor deposition reactor, using sequential group III (trimethylgallium, TMG) and group V (arsine) reactant gas exposures typical of atomic layer epitaxy (ALE). The results show that, at a given temperature, impurity (e.g., carbon) incorporation is controlled by the effective V/III ratio at the growing surface, which is determined by the sequence used in the growth cycles. This effect, specific to ALE, is quantified by solving the diffusion equation that describes concentration transients at the growing surface. Detailed photoluminescence experiments identified C and Mg as the residual acceptors and Ge as the sole residual donor in a 3×1015 cm−3 n‐type background layer with mobilities of 5600 cm2/V s at room temperature and 35 000 cm2/V s at 77 K. A higher purity sample showed reduced levels of Ge, with traces of S, Si, and Te donors and only C acceptors.
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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.
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.55.Cr III-V semiconductors

Magnetization and critical current density of the Bi‐(Pb)‐Sr‐Ca‐Cu‐O tapes in magnetic fields

H. Sekine, K. Itoh, K. Inoue, H. Maeda, and K. Numata

Appl. Phys. Lett. 55, 2772 (1989); http://dx.doi.org/10.1063/1.101950 (3 pages) | Cited 2 times

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The Bi‐(Pb)‐Sr‐Ca‐Cu‐O superconductor was fabricated into tapes with a Cu sheath. Measurements of magnetization and critical current density Jc in magnetic fields up to 23 T were made for them. The magnetization measurement revealed that, at 4.2 K, these tape specimens had excellent Jc ‐H(magnetic field) characteristics, while at 77 K, the flux pinning force in them was reduced to zero above 0.3 T due to the flux creep. In the resistive Jc measurement at 4.2 K, these tape specimens showed Jc of ∼7000 A/cm2 at 23. The Jc ‐H curve showed a slight peak effect, indicating the peak over 30 T.
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74.70.-b Superconducting materials other than cuprates
74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)

Structural study of undoped and doped Bi2Sr2CuO6 phases by transmission electron microscopy

J. G. Wen, Y. Liu, Z. F. Ren, Y. F. Yan, Y. Q. Zhou, and K. K. Fung

Appl. Phys. Lett. 55, 2775 (1989); http://dx.doi.org/10.1063/1.102371 (3 pages) | Cited 4 times

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Bi‐based superconducting phases have been studied by transmission electron microscopy. The strong one‐dimensional modulations in undoped and Ce‐doped monoclinic Bi2 Sr2 CuO6 (2201) samples are different from one another. We have found a new 2201 phase containing Pb and Ca with orthorhombic symmetry in nominal (Bi0.90 Pb0.10 )2 Sr2 CaCu2 O8 crystals. Its structure with space group Bbmb and two‐dimensional modulation are analogous to those of the Pb‐doped higher members of the structural series Bi2 Sr2 Can−1 Cun O2n+4 . Hence, this new orthorhombic rather than the monoclinic 2201 phase should be the first member of the structural series.
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74.70.-b Superconducting materials other than cuprates
07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination
61.66.Fn Inorganic compounds
74.20.Mn Nonconventional mechanisms
74.20.Rp Pairing symmetries (other than s-wave)

New hybrid physical vapor deposition/organometallic chemical vapor deposition route to high Tc superconducting Tl‐Ba‐Ca‐Cu‐O thin films

D. S. Richeson, L. M. Tonge, X. K. Wang, H. O. Marcy, T. J. Marks, J. B. Ketterson, R. P. H. Chang, and C. R. Kannewurf

Appl. Phys. Lett. 55, 2778 (1989); http://dx.doi.org/10.1063/1.102372 (3 pages) | Cited 16 times

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High Tc superconducting Tl‐Ba‐Ca‐Cu‐O thin films have been prepared by a novel hybrid technique that combines electron beam evaporation with organometallic chemical vapor deposition (OMCVD). Multilayer thin films of Ba‐Ca‐Cu‐O are prepared by sequential evaporation of BaF2, CaF2, and Cu sources onto single‐crystal MgO (100) or yttria‐stabilized zirconia substrates followed by annealing in a water vapor‐saturated oxygen atmosphere. Thallium is then incorporated in these films in either of two ways: (1) OMCVD using thallium(cyclopentadienide) as the source or (2) vapor diffusion using bulk Tl‐Ba‐Ca‐Cu‐O superconductor as the source. The resultant films are single phase, consisting predominantly of Tl1Ba2Ca2Cu3Ox with crystallite Cu‐O planes preferentially oriented parallel to the substrate surface. Resistivity measurements indicate superconducting onset temperatures above 120 K with zero resistance by 104 K. By eliminating the water vapor in the initial anneal, fluoride (originating from the Ba and Ca sources) may be retained in the film. Upon T1 incorporation, this promotes formation of the Tl1Ba2Ca1Cu2Ox phase with preferential crystallite c‐axis orientation perpendicular to the substrate surface.
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74.70.-b Superconducting materials other than cuprates
74.78.-w Superconducting films and low-dimensional structures
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Grain size dependence of the critical current density in YBa2Cu3Ox superconductors

M. Kuwabara and H. Shimooka

Appl. Phys. Lett. 55, 2781 (1989); http://dx.doi.org/10.1063/1.102373 (3 pages) | Cited 17 times

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The grain size dependence of the critical current density in bulk single‐phase YBa2Cu3Ox ceramics was investigated. The grain size of the materials was changed to range approximately from 1.0 to 25 μm by changing the conditions of power processing and sintering, associated with an increase in the sintered density of the materials with increasing grain size. The critical current density has been found to exhibit a significant grain size dependence, changing from 880 A/cm2 to a value of 100 A/cm2 with a small increase in the average grain size from 1.2 to 2.0 μm. This seems to provide information about the nature of the weak link between superconducting grains which might govern the critical current density of the materials.
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74.25.Sv Critical currents
74.70.-b Superconducting materials other than cuprates
61.72.Mm Grain and twin boundaries
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition

Levitation properties of the YBa2Cu3Ox and Tl‐Ba‐Ca‐Cu‐O superconducting systems

David E. Weeks

Appl. Phys. Lett. 55, 2784 (1989); http://dx.doi.org/10.1063/1.102374 (3 pages) | Cited 10 times

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A torsion balance is used to measure the levitation force on a magnet as a function of height above bulk samples of the YBa2Cu3Ox (Tc∼90 K) and Tl‐Ba‐Ca‐Cu‐O (Tc∼110–120 K) superconducting systems. Measurements of magnetic shielding and trapped magnetic fields are also made.
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74.70.-b Superconducting materials other than cuprates
74.25.-q Properties of superconductors
74.25.N- Response to electromagnetic fields

Electrical charging of percolating samples in the scanning electron microscope

Z. Barkay, B. Dwir, G. Deutscher, and E. Grünbaum

Appl. Phys. Lett. 55, 2787 (1989); http://dx.doi.org/10.1063/1.101909 (3 pages) | Cited 3 times

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Electrical properties of indium percolating samples were investigated by the charging effect in the scanning electron microscope. The finite clusters and the infinite cluster were identified due to the difference in their charging images. The finite clusters exhibited a capacitor‐like behavior. An electric breakdown in a tree‐like structure was obtained in the indium insulating films.
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73.61.At Metal and metallic alloys
07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination
68.35.B- Structure of clean surfaces (and surface reconstruction)
73.61.Ng Insulators

Ultrafast imaging of ultraviolet laser ablation and etching of polymethylmethacrylate

R. Srinivasan, Bodil Braren, Kelly G. Casey, and Mildred Yeh

Appl. Phys. Lett. 55, 2790 (1989); http://dx.doi.org/10.1063/1.101910 (2 pages) | Cited 51 times

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Ablation and etching of the surface of polymethylmethacrylate (PMMA) by pulses of 248 nm laser radiation [∼20 ns full width at half maximum (FWHM)] have been probed by pulses of visible laser radiation (596 nm; <1 ns FWHM). The results were recorded photographically. Modification of the surface structure of the polymer is first visible at 12 ns and appears to be complete in about 60 ns. Emerging solid material, preceded by a shock wave which first becomes visible at 60 ns, reaches a maximum in intensity at 6 μs and continues until about 20 μs. The average velocity of the solid material, which is probably a low molecular weight polymer of PMMA, is 1.5×104 cm/s.
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79.20.Ds Laser-beam impact phenomena
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments
68.35.B- Structure of clean surfaces (and surface reconstruction)
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