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4 Sep 2000

Volume 77, Issue 10, pp. 1413-1560

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Infrared absorption peak due to Ta=O bonds in Ta2O5 thin films

Haruhiko Ono and Ken-ichi Koyanagi

Appl. Phys. Lett. 77, 1431 (2000); http://dx.doi.org/10.1063/1.1290494 (3 pages) | Cited 20 times

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Ta2O5 films deposited on Si substrates were investigated using transmission Fourier-transform infrared spectroscopy. We found a new absorption peak at 2340 cm−1 that can be characterized as a stretching vibration mode due to Ta=O bonds in the films. This peak appeared following annealing in O2 ambient, but not in N2 ambient. It was located at 2335 cm−1 in amorphous Ta2O5 films and shifted to 2340 cm−1 after crystallization by annealing at over 700 °C. The bonds associated with the peak were homogeneously distributed in the film. We demonstrated that Ta2O5 films can include strong double bonds between Ta and O (Ta=O) in the structure, independent of whether they are crystalline or amorphous. © 2000 American Institute of Physics.
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78.66.Nk Insulators
68.55.-a Thin film structure and morphology
61.50.Lt Crystal binding; cohesive energy
78.30.Hv Other nonmetallic inorganics

Thermal expansion of bulk and homoepitaxial GaN

V. Kirchner, H. Heinke, D. Hommel, J. Z. Domagala, and M. Leszczynski

Appl. Phys. Lett. 77, 1434 (2000); http://dx.doi.org/10.1063/1.1290491 (3 pages) | Cited 13 times

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The thermal behavior of Mg-doped and intentionally undoped bulk crystals and homoepitaxial GaN was investigated in a wide temperature range from 12 to 600 K. With high-resolution x-ray diffraction, both lattice parameters a and c were determined and the thermal expansion coefficients were calculated. Within the experimental accuracy, mean values were extracted for the temperature ranges 12–100, 100–250, and 250–600 K. These values are essential, especially, for the interpretation of measurements of other GaN properties performed at low temperatures. © 2000 American Institute of Physics.
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65.40.De Thermal expansion; thermomechanical effects
68.60.Dv Thermal stability; thermal effects
61.66.Fn Inorganic compounds
68.55.-a Thin film structure and morphology

Effect of oxidation and reoxidation on the oxide-substrate interface of 4H- and 6H-SiC

G. G. Jernigan, R. E. Stahlbush, and N. S. Saks

Appl. Phys. Lett. 77, 1437 (2000); http://dx.doi.org/10.1063/1.1290490 (3 pages) | Cited 23 times

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X-ray photoelectron spectroscopy and sputter depth profiling were used to investigate SiO2 grown on 4H- and 6H-SiC with and without a reoxidation procedure. The oxides grown and oxide-substrate interfaces formed on 4H and 6H were similar in chemistry but different from Si(100). Reoxidation changes the structure of the oxide and the abruptness of the oxide-substrate interface. We propose a model for SiC oxidation where a transition layer containing Si–Si bonds is produced between the oxide and the SiC substrate.
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81.65.Mq Oxidation
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
68.35.Ct Interface structure and roughness
79.60.Jv Interfaces; heterostructures; nanostructures
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
73.20.-r Electron states at surfaces and interfaces

Biphotonic holographic gratings in azobenzene polyesters: Surface relief phenomena and polarization effects

C. Sánchez, R. Alcalá, S. Hvilsted, and P. S. Ramanujam

Appl. Phys. Lett. 77, 1440 (2000); http://dx.doi.org/10.1063/1.1290604 (3 pages) | Cited 17 times

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Biphotonic holographic gratings have been recorded in a side-chain azobenzene liquid crystalline polyester using a blue incoherent source and a He–Ne laser. Intensity gratings and the appearance of surface relief have been observed when two linearly polarized beams from a He–Ne laser are made to interfere on a film illuminated with blue light. Polarized holographic gratings are also created with two orthogonally circularly polarized He–Ne beams. All these gratings are stable in darkness but can be erased with blue light. © 2000 American Institute of Physics.
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42.40.Eq Holographic optical elements; holographic gratings
42.70.Jk Polymers and organics
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.25.H- Macromolecular and polymers solutions; polymer melts
61.30.-v Liquid crystals

Reaction of Co and capping layers and its effect on CoSi2 formation in Si/SiOx/Co system

Gi Bum Kim, Joon Seop Kwak, Hong Koo Baik, Sung Man Lee, Sang Ho Oh, and Chan Gyung Park

Appl. Phys. Lett. 77, 1443 (2000); http://dx.doi.org/10.1063/1.1290689 (3 pages) | Cited 4 times

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The role of the reaction between the capping layer and Co on the crystalline nature of CoSi2 films in refractory metal-capped Si/SiOx/Co system has been investigated. The epitaxial CoSi2 film was obtained in the capping layers (Ti, Zr) with high tendency of mixing between Co and the capping layer. Amorphous Ti–Co layer was produced at 450 °C, and its thickness was increased at 550 °C. The formation of amorphous Ti–Co layer during low-temperature annealing may be responsible for the formation of epitaxial CoSi2. Meanwhile, the polycrystalline CoSi2 was formed in the capping layer (Cr, Mo) with low tendency of mixing. These results can be explained by the fact that the mixing layer formed from the reaction between Co and refractory metal control the Co diffusion to the Si substrate as well as the thin SiOx between Co and Si. © 2000 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
61.72.Cc Kinetics of defect formation and annealing

Coupling of kinetic and transport phenomena in self-organization of C–B–N nanotube growth into sandwich structures

Oleg A. Louchev, Yoichiro Sato, Hisao Kanda, and Yoshio Bando

Appl. Phys. Lett. 77, 1446 (2000); http://dx.doi.org/10.1063/1.1290600 (3 pages) | Cited 8 times

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A mechanism for self-organization of C–B–N sandwich-like nanotubes with well-separated phases of C and BN [K. Suenaga, C. Colliex, N. Demoncy, A. Loiseau, H. Pascard, F. Willaime, Science 278, 653 (1997)] in arc-discharge is proposed. This mechanism includes (i) the microkinetic self-organization of nanotube growth in step-flow mode combined with a C and BN phase segregation at growth steps and (ii) the self-organization of “macro”-oscillations of impinging fluxes of C and B on the surface of nanotubes, which are caused by the nonuniformity of C and B content in the gas combined with the onset of natural convection, providing repeated transport of emerging nanotubes through regions with abundance in C and B, and leading to nucleation and growth of C and BN layers. © 2000 American Institute of Physics.
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81.05.ub Fullerenes and related materials
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
64.75.-g Phase equilibria
81.30.Mh Solid-phase precipitation
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Growth of step-free surfaces on device-size (0001)SiC mesas

J. Anthony Powell, Philip G. Neudeck, Andrew J. Trunek, Glenn M. Beheim, Lawrence G. Matus, Richard W. Hoffman, and Luann J. Keys

Appl. Phys. Lett. 77, 1449 (2000); http://dx.doi.org/10.1063/1.1290717 (3 pages) | Cited 36 times

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It is believed that atomic-scale surface steps cause defects in single-crystal films grown heteroepitaxially on SiC substrates. A method is described whereby surface steps can be grown out of existence on arrays of device-size mesas on commercial “on-axis” SiC wafers. Step-free mesas with dimensions up to 200 μm square have been produced on 4H-SiC wafers and up to 50 μm square on a 6H-SiC wafer. A limiting factor in scaling up the size and yield of the step-free mesas is the density of screw dislocations in the SiC wafers. The fundamental significance of this work is that it demonstrates that two-dimensional nucleation of SiC can be suppressed while carrying out step-flow growth on (0001)SiC. The application of this method should enable the realization of improved heteroepitaxially-grown SiC and GaN device structures. © 2000 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Lk Linear defects: dislocations, disclinations

Temperature dependence of the transition from two-dimensional to three-dimensional growth of Ge on (001)Si studied by reflection high-energy electron diffraction

V. Cimalla and K. Zekentes

Appl. Phys. Lett. 77, 1452 (2000); http://dx.doi.org/10.1063/1.1290720 (3 pages) | Cited 8 times

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Germanium islands have been grown on Si(001) by solid-source molecular-beam epitaxy at temperatures between 325 and 900 °C. The formation of metastable {105} faceted clusters and macroislands was investigated by real-time reflection high-energy electron diffraction. Up to 600 °C, the two-dimensional (2D)-three-dimensional (3D) growth transition through the formation of hut clusters appears at a temperature-independent critical thickness, while the coalescence to macroislands is thermally activated. An activation barrier was also found for the 2D–3D growth transition directly to macroislands at growth temperatures above 600 °C. The crossing of the two competing transitions at 600 °C determines the two growth regimes. © 2000 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Ion-beam-induced porosity of GaN

S. O. Kucheyev, J. S. Williams, C. Jagadish, J. Zou, V. S. J. Craig, and G. Li

Appl. Phys. Lett. 77, 1455 (2000); http://dx.doi.org/10.1063/1.1290722 (3 pages) | Cited 41 times

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Wurtzite GaN films bombarded with heavy ions (197Au+) show anomalous swelling of the implanted region with corresponding volume expansion up to ∼ 50%. Results show that this phenomenon is due to the formation of a porous layer of amorphous GaN. An important implication of this study for the fabrication of GaN-based devices is that amorphization of GaN should be avoided during ion implantation. © 2000 American Institute of Physics.
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61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.72.uj III-V and II-VI semiconductors
61.43.Dq Amorphous semiconductors, metals, and alloys

Maximized sp3 bonding in carbon nitride phases

S. E. Rodil, W. I. Milne, J. Robertson, and L. M. Brown

Appl. Phys. Lett. 77, 1458 (2000); http://dx.doi.org/10.1063/1.1308273 (3 pages) | Cited 22 times

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Carbon nitride films were deposited using a low pressure, dual ion beam system consisting of a filtered cathodic vacuum arc and a plasma beam source for carbon and nitrogen ions, respectively. This system maintains highly ionized beams even at high nitrogen fluxes, unlike in single beam systems. Film composition and bonding were measured by electron energy loss spectroscopy. Films with nitrogen to carbon atom ratios (N/C) up to 0.5 are produced. The carbon bonding is found to change gradually from sp3 to sp2, rather than sharply above a critical N content, as found previously. This indicates that N atoms form individual C�N bonds rather than causing a reversion of the entire C network to sp2. This allows us to maintain C sp3 bonding to the highest N contents so far achieved. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.55.Nq Composition and phase identification
79.20.Kz Other electron-impact emission phenomena
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition

Observation and first-principles calculation of buried wurtzite phases in zinc-blende CdTe thin films

Y. Yan, M. M. Al-Jassim, K. M. Jones, S.-H. Wei, and S. B. Zhang

Appl. Phys. Lett. 77, 1461 (2000); http://dx.doi.org/10.1063/1.1308062 (3 pages) | Cited 17 times

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We report direct observation of the existence of buried thin wurtzite CdTe layers in nominally pure zinc-blende CdTe thin films using high-resolution transmission electron microscopy. The formation of the buried wurtzite layers is a result of the formation of high density of planar defects in the zinc-blende films—the wurtzite layers are formed by closely spaced lamellar twins. First-principles calculations reveal that the presence of the buried wurtzite layers may be responsible for the poor electrical properties of the polycrystalline zinc-blende CdTe films. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Thermal conductivity of fully and partially coalesced lateral epitaxial overgrown GaN/sapphire (0001) by scanning thermal microscopy

D. I. Florescu, V. M. Asnin, Fred H. Pollak, A. M. Jones, J. C. Ramer, M. J. Schurman, and I. Ferguson

Appl. Phys. Lett. 77, 1464 (2000); http://dx.doi.org/10.1063/1.1308057 (3 pages) | Cited 45 times

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We have measured high spatial/depth resolution (∼2–3 μm) thermal conductivity (κ) at 300 K of both fully and partially coalesced GaN/sapphire (0001) samples fabricated by lateral epitaxial overgrowth. On the fully coalesced sample we found 1.86W/cm K<κ<2.05 W/cm K over a distance of approximately 50 μm. One of the partially coalesced samples had 2.00 W/cm K<κ<2.10 W/cm K on the overgrown regions, as identified by atomic force microscopy imaging. These latter results are the highest thermal conductivity values reported on GaN material. A correlation between low threading dislocation density and high thermal conductivity values was established. © 2000 American Institute of Physics.
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68.60.Dv Thermal stability; thermal effects
68.55.-a Thin film structure and morphology
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

High-energy-resolution scintillator: Ce3+ activated LaCl3

E. V. D. van Loef, P. Dorenbos, C. W. E. van Eijk, K. Krämer, and H. U. Güdel

Appl. Phys. Lett. 77, 1467 (2000); http://dx.doi.org/10.1063/1.1308053 (2 pages) | Cited 61 times

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The scintillation properties of LaCl3 doped with 10% Ce3+ are presented. Under optical and gamma ray excitation, Ce3+ emission is observed to peak at 330 and 352 nm. The scintillation light output is 46 000±1000 photons/MeV at 662 keV. Forty percent is emitted with a decay time of 26 ns, 30% with 210 ns, and 30% with about 1000 ns. An energy resolution (full width at half maximum over the peak position) of 3.3±0.3% was observed for the 662 keV full absorption peak. © 2000 American Institute of Physics.
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78.55.Hx Other solid inorganic materials

Paramagnetic defects at the interface of ultrathin oxides grown under vacuum ultraviolet photon excitation on (111) and (100) Si

A. Stesmans and V. V. Afanas’ev

Appl. Phys. Lett. 77, 1469 (2000); http://dx.doi.org/10.1063/1.1289265 (3 pages) | Cited 20 times

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Electron-spin-resonance monitoring of Si dangling-bond-type interface defects is used to study ultrathin (∼20 Å) Si-oxide films grown by vacuum ultraviolet (VUV)-enhanced oxidation of Si at 300 K. Large densities (up to ∼ 9×1012 cm−2) of Pb and Pb0 centers (interfacial Si3�Si⋅) are observed in VUV-grown (111) and (100) Si/SiO2, respectively. As compared to standard thermal Si/SiO2, two major differences emerge: the VUV Si/SiO2 interface is under substantially enhanced stress, while no Pb1 defects are discerned in VUV (100) Si/SiO2. It is inferred that Pb1 generation requires a minimum amount of oxide relaxation. Microscopic understanding is provided for the known inferior electrical interface quality threatening low-thermal-budget oxide fabrication. © 2000 American Institute of Physics.
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68.35.Ct Interface structure and roughness
81.05.Cy Elemental semiconductors
81.65.Mq Oxidation
82.50.-m Photochemistry
76.30.Mi Color centers and other defects
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
68.35.Gy Mechanical properties; surface strains
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