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12 Mar 2001

Volume 78, Issue 11, pp. 1463-1639

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Near-field photocurrent imaging of the optical mode profiles of semiconductor laser diodes

T. Guenther, V. Malyarchuk, J. W. Tomm, R. Müller, C. Lienau, and J. Luft

Appl. Phys. Lett. 78, 1463 (2001); http://dx.doi.org/10.1063/1.1342206 (3 pages) | Cited 4 times

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The potential of near-field photocurrent spectroscopy for direct imaging of mode profiles of submicron-sized waveguides in optoelectronic devices is demonstrated. The technique combines the submicron spatial resolution of near-field optics with tunable laser excitation, allowing for selective investigation of the waveguide properties of the device structure. Experiments on InGaAs/AlGaAs high-power laser diodes with different waveguide designs provide direct visualization of the effect of the waveguide design on (i) the number of guided modes and (ii) the spatial profile of both fundamental and higher-order modes. The technique thus provides a sensitive tool for nondestructive in situ analysis of waveguide properties in optoelectronic devices. © 2001 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.82.Bq Design and performance testing of integrated-optical systems
07.79.Fc Near-field scanning optical microscopes

Photonic crystal waveguides: Out-of-plane losses and adiabatic modal conversion

M. Palamaru and Ph. Lalanne

Appl. Phys. Lett. 78, 1466 (2001); http://dx.doi.org/10.1063/1.1354666 (3 pages) | Cited 67 times

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An accurate model for the out-of-plane radiation losses occurring when a guided wave propagating in a conventional waveguide impinges on a photonic crystal waveguide is presented. The model makes clear that the losses originate from insertion losses resulting from a mode mismatch. A generic taper structure realizing an adiabatic modal conversion is proposed and validated through numerical computations for cavities with large Q’s and large peak transmission. © 2001 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
42.50.-p Quantum optics
42.70.Qs Photonic bandgap materials
42.82.Et Waveguides, couplers, and arrays

Stimulated emission and optical gain in ZnO epilayers grown by plasma-assisted molecular-beam epitaxy with buffers

Yefan Chen, N. T. Tuan, Yusaburo Segawa, Hang-ju Ko, Soon-ku Hong, and Takafumi Yao

Appl. Phys. Lett. 78, 1469 (2001); http://dx.doi.org/10.1063/1.1355665 (3 pages) | Cited 85 times

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We report the results of an experimental investigation on lasing mechanisms in optically pumped ZnO epilayers at room temperature. High-quality ZnO epilayers grown on sapphire by plasma-assisted molecular-beam epitaxy employing an MgO buffer were used. Free exciton emissions and their phonon replicas dominate the photoluminescence from low excited samples. Inelastic exciton–exciton scattering contributes to the mechanism of stimulated emission mainly at intermediate excitation. By using the variable stripe length method, we measured the near threshold optical gain spectrum of the ZnO epilayers. Different from the interband transition governed mechanisms, exciton–exciton scattering gives rise to a nearly symmetric gain spectrum with the peak at 3.17 eV. The electron-hole plasma emerges to contribute to the optical gain when excitation exceeds 220 kW/cm2. © 2001 American Institute of Physics.
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78.45.+h Stimulated emission
78.66.Hf II-VI semiconductors
42.55.Px Semiconductor lasers; laser diodes
78.55.Et II-VI semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
63.20.kk Phonon interactions with other quasiparticles

Birefringence evaluation of multimode multilayer AlGaAs/AlAs waveguides

G. Leo, M. Secondini, M. Morabito, A. De Rossi, G. Assanto, A. Fiore, V. Berger, M. Calligaro, and J. Nagle

Appl. Phys. Lett. 78, 1472 (2001); http://dx.doi.org/10.1063/1.1355005 (3 pages) | Cited 4 times

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We investigate surface-emitting second harmonic generation as a powerful technique for the evaluation of birefringence in optical waveguides supporting several modes. This one-shot diagnostic is demonstrated at 1319 nm in multilayer AlGaAs waveguides, before and after the lateral oxidation of AlAs layers. © 2001 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
78.20.Fm Birefringence
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Wi Nonlinear waveguides
42.79.Wc Optical coatings
78.66.Fd III-V semiconductors

Photonic-crystal distributed-feedback lasers

I. Vurgaftman and J. R. Meyer

Appl. Phys. Lett. 78, 1475 (2001); http://dx.doi.org/10.1063/1.1355670 (3 pages) | Cited 17 times

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The far-field emission characteristics and spectral purity of photonic-crystal distributed-feedback (PCDFB) lasers, in which the grating is defined on a two-dimensional lattice that is tilted with respect to the facets, are analyzed using a self-consistent time-domain simulation. It is shown that both conventional DFB and angled-grating DFB devices are special cases of the PCDFB laser, which combines and enhances the best features of each. The simulations project both high beam quality and high spectral purity out to pump stripes of width ≫100 μm. © 2001 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.70.Qs Photonic bandgap materials

Morphology and photonic band structure modification of polystyrene particle layers by reactive ion etching

Toru Fujimura, Tsuyoshi Tamura, Tadashi Itoh, Chiseki Haginoya, Yuri Komori, and Takao Koda

Appl. Phys. Lett. 78, 1478 (2001); http://dx.doi.org/10.1063/1.1353844 (3 pages) | Cited 15 times

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Morphology of self-assembled polystyrene particle layers has been modified by reactive ion etching. The etched layers have two-dimensional periodic structures in submicron scale, the period of which is determined by the initial size of the particles, and the shape of the etched particles has been gradually changed to a thinner ellipsoid depending on the etching time. Resonant phenomenon between incident light and electromagnetic eigenmodes of the photonic band of the etched layers has been observed in transmission measurement. The resonant frequencies have gradually shifted according to the etching time, i.e., the photonic band structure of the layers has been successfully modified. Various kinds of applications can be expected due to the electromagnetic resonant phenomenon and the characteristic surface structure of the layers. © 2001 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
81.65.Cf Surface cleaning, etching, patterning
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
68.47.Mn Polymer surfaces
61.41.+e Polymers, elastomers, and plastics
42.70.Jk Polymers and organics
78.66.Qn Polymers; organic compounds

Spatial domain realization of the cavity ring-down technique in a plane Fabry–Perot cavity

Jae Yong Lee, Hai-Woong Lee, and Jae Won Hahn

Appl. Phys. Lett. 78, 1481 (2001); http://dx.doi.org/10.1063/1.1342039 (3 pages) | Cited 2 times

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We propose and demonstrate a spatial version of the cavity ring-down concept in which a photon flux decay is displayed along the spatial coordinate at the exit of a plane Fabry–Perot cavity. The photon decay signals are simulated based on a simple theoretical model combining ray optics and diffraction involved in the spatial ring-down generation, which are found to be in good accordance with the results of a proof-of-principle expermient. © 2001 American Institute of Physics.
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07.60.Rd Visible and ultraviolet spectrometers
07.60.Ly Interferometers
42.15.Dp Wave fronts and ray tracing
42.25.Fx Diffraction and scattering

Laser micromachining using liquid optics

D. Ramanathan and P. A. Molian

Appl. Phys. Lett. 78, 1484 (2001); http://dx.doi.org/10.1063/1.1351844 (3 pages) | Cited 5 times

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Lasers are well suited for micromanufacturing by ablating nearly all the material within the focal spot before any significant heat conduction or mass flow takes place, thus enabling precise machining with little thermal damage. In this letter, the results of an idea of using nonlinear liquids as lenses to fabricate micron-sized features are reported. Our research showed that transmitting the laser pulse through a transparent condensed medium such as carbon disulfide that has very high intensity-dependent nonlinear refractive index creates a lens and focuses the beam. Results on 316 stainless steel showed a two-fold decrease in the hole size and reduced taper when liquid optics were used over traditional solid optics. Polarization effects were also substantially reduced. The beneficial effects of liquid optics are explored. © 2001 American Institute of Physics.
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42.62.Cf Industrial applications
42.79.Bh Lenses, prisms and mirrors
81.20.Wk Machining, milling
06.60.Vz Workshop procedures (welding, machining, lubrication, bearings, etc.)

Coupled guide and cavity in a two-dimensional photonic crystal

C. J. M. Smith, R. M. De La Rue, M. Rattier, S. Olivier, H. Benisty, C. Weisbuch, T. F. Krauss, R. Houdré, and U. Oesterle

Appl. Phys. Lett. 78, 1487 (2001); http://dx.doi.org/10.1063/1.1355667 (3 pages) | Cited 55 times

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We demonstrate, in a planar two-dimensional (2D) configuration, in the optical regime a clear association of two photonic crystal elements and the ability to produce a low-loss coupled system. A channel waveguide is brought to between two and five crystal rows (450 to 1126 nm) from a 2D microcavity fabricated in a GaAs/AlGaAs waveguide. We probe these two elements individually and explore their interaction. © 2001 American Institute of Physics.
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42.82.Et Waveguides, couplers, and arrays
85.60.Bt Optoelectronic device characterization, design, and modeling
78.67.Hc Quantum dots
42.79.Gn Optical waveguides and couplers
81.05.Ea III-V semiconductors
81.07.Ta Quantum dots
42.70.Qs Photonic bandgap materials

A photopolymerizable glass with diffraction efficiency near 100% for holographic storage

Pavel Cheben and María L. Calvo

Appl. Phys. Lett. 78, 1490 (2001); http://dx.doi.org/10.1063/1.1354665 (3 pages) | Cited 57 times

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Permanent holographic storage has been demonstrated in a photopolymerizable organically modified silica glass. The glass was prepared by dispersing a titanocene photoinitiator and a high refractive index acrylic monomer in a porous silica matrix. This glass exhibits unprecedented sensitivity and refractive index change upon a moderate exposure to green light and can be fabricated in thickness up to several millimeters. A photopolymerizable storage medium of such a thickness with good holographic properties is needed for practical holographic storage devices. Lack of such medium has been considered the main obstacle in development of write-once holographic memories. In our glass, we have stored permanent volume holograms of diffraction efficiency approaching 100% and refractive index modulation up to 4.5×10−3, making this photopolymerizable material suitable for use in holographic data storage. © 2001 American Institute of Physics.
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42.70.Ln Holographic recording materials; optical storage media
42.79.Vb Optical storage systems, optical disks
42.70.Ce Glasses, quartz
42.70.Jk Polymers and organics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
82.50.Hp Processes caused by visible and UV light
82.35.-x Polymers: properties; reactions; polymerization

Multicolor oligothiophene-based light-emitting diodes

G. Gigli, O. Inganäs, M. Anni, M. De Vittorio, R. Cingolani, G. Barbarella, and L. Favaretto

Appl. Phys. Lett. 78, 1493 (2001); http://dx.doi.org/10.1063/1.1355991 (3 pages) | Cited 35 times

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We demonstrate wide tunability, from green to near infrared, of the electroluminescence emission of substituted oligothiophene compounds. The compounds are characterized by high chemical stability, electron affinities up to 3.1 eV and photoluminescence efficiencies up to 70%. These characteristics make these materials excellent candidates for application in light-emitting diodes. We obtain low turn-on voltage devices with electroluminescence efficiency up to 0.2%, more than one order of magnitude larger than the values reported for unsubstituted oligothiophene compounds. © 2001 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.55.Kz Solid organic materials
42.70.Jk Polymers and organics

High-precision ranging using a chaotic laser pulse train

Krishna Myneni, Thomas A. Barr, Billy R. Reed, Shawn D. Pethel, and Ned J. Corron

Appl. Phys. Lett. 78, 1496 (2001); http://dx.doi.org/10.1063/1.1355663 (3 pages) | Cited 13 times

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We demonstrate the use of a chaotic laser pulse train for high-precision ranging. The pulse train is produced by inducing coherence collapse in an AlGaAs semiconductor laser. Measurements of optical spectra, intensity autocorrelation functions, and ladar ranging are presented. © 2001 American Institute of Physics.
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06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
42.79.Qx Range finders, remote sensing devices; laser Doppler velocimeters, SAR, and LIDAR
42.55.Px Semiconductor lasers; laser diodes
42.25.Kb Coherence
42.65.Sf Dynamics of nonlinear optical systems; optical instabilities, optical chaos and complexity, and optical spatio-temporal dynamics
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Role of the kinetic and potential sputtering in the regeneration of the soot

Shoaib Ahmad and M. N. Akhtar

Appl. Phys. Lett. 78, 1499 (2001); http://dx.doi.org/10.1063/1.1354661 (3 pages) | Cited 4 times

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We have used the photoemission spectroscopy of the graphite hollow cathode sooting discharge to identify the roles played by the kinetic and potential sputtering, respectively. Our indicators are the relative densities of the sputtered carbon C, the Ne metastable atoms, and the ionized components (Ne+) of the regenerative sooting plasma. We find that the metastable atoms are the main agents for the regeneration of the soot. © 2001 American Institute of Physics.
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81.05.U- Carbon/carbon-based materials
52.80.Hc Glow; corona
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
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Enhancing the active lifetime of luminescent semiconducting polymers via doping with metal nanoshells

G. D. Hale, J. B. Jackson, O. E. Shmakova, T. R. Lee, and N. J. Halas

Appl. Phys. Lett. 78, 1502 (2001); http://dx.doi.org/10.1063/1.1343854 (3 pages) | Cited 29 times

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We report a dramatic, concentration-dependent decrease in the rate of photo-oxidation of semiconducting polymers due to the addition of small amounts of metal nanoshells to the polymer. In each case, the nanoshell resonances are tuned to the triplet exciton-ground state energy of the polymer. The nanoshell dopants slow the oxidation rate yet do not affect the photoluminescent properties of the polymers to which they have been added. © 2001 American Institute of Physics.
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61.72.up Other materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
85.40.Ry Impurity doping, diffusion and ion implantation technology
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
71.20.Rv Polymers and organic compounds
78.66.Qn Polymers; organic compounds
61.41.+e Polymers, elastomers, and plastics
82.35.Cd Conducting polymers
81.16.Pr Micro- and nano-oxidation
81.65.Mq Oxidation
82.50.-m Photochemistry
82.20.Pm Rate constants, reaction cross sections, and activation energies
71.35.-y Excitons and related phenomena
78.55.Kz Solid organic materials
61.46.-w Structure of nanoscale materials
61.82.Rx Nanocrystalline materials
81.07.Bc Nanocrystalline materials
71.55.Ht Other nonmetals

Doping by metal-mediated epitaxy: Growth of As delta-doped Si through a Pb monolayer

O. D. Dubon, P. G. Evans, J. F. Chervinsky, M. J. Aziz, F. Spaepen, J. A. Golovchenko, M. F. Chisholm, and D. A. Muller

Appl. Phys. Lett. 78, 1505 (2001); http://dx.doi.org/10.1063/1.1352692 (3 pages) | Cited 5 times

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In molecular-beam epitaxy a monolayer of Pb on the Si(111) surface induces single-crystal growth at temperatures well below those required for similar growth on a bare surface. We demonstrate that the suppression of dopant segregation at the lower temperatures attainable by Pb-mediated growth allows the incorporation of As donors at concentrations reaching a few atomic percent. When Pb and Si are deposited on an As-terminated Si(111) substrate at 350 °C, the Pb segregates to the surface without doping the Si film while the As is buried within nanometers of the substrate–film interface. The resulting concentration of electrically active As, 1.8×1021 cm−3, represents the highest concentration of As donors achieved by any delta-doping or thin-film deposition method. © 2001 American Institute of Physics.
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61.72.uf Ge and Si
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Cy Elemental semiconductors
68.35.Dv Composition, segregation; defects and impurities
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
85.40.Ry Impurity doping, diffusion and ion implantation technology

Near-field photoluminescence study of GaNAs alloy epilayer at room and cryogenic temperature

K. Matsuda, T. Saiki, M. Takahashi, A. Moto, and S. Takagishi

Appl. Phys. Lett. 78, 1508 (2001); http://dx.doi.org/10.1063/1.1353815 (3 pages) | Cited 27 times

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We have measured the spatial distribution of the optical properties of a GaNAs (N∼0.8%) epilayer to investigate the carrier recombination mechanism at both room temperature and cryogenic temperature using a near-field scanning optical microscope. A difference between the macro and near-field photoluminescence (PL) spectra at room temperature was not observed. At low temperature, we found spatial inhomogeneity of the optical properties and sharp features in the near-field PL spectrum. These findings indicate that the dominant emission mechanism changes from recombination of delocalized carriers at room temperature to recombination of localized carriers (excitons) trapped in the local potential minimum due to compositional fluctuation at low temperature. © 2001 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors

Epitaxial growth of ZnO films on Si substrates using an epitaxial GaN buffer

Ahmed Nahhas, Hong Koo Kim, and Jean Blachere

Appl. Phys. Lett. 78, 1511 (2001); http://dx.doi.org/10.1063/1.1355296 (3 pages) | Cited 49 times

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We report on epitaxial growth of ZnO films on Si(111) substrates using an epitaxial GaN buffer layer. A rf magnetron sputtering process has been developed and utilized in growing epitaxial GaN buffers on Si, and then ZnO films on the GaN-buffered Si substrates. X-ray diffraction analysis shows that both the ZnO and GaN films are of a monocrystalline wurtzite structure with an epitaxial relationship of ZnO[0001]//GaN[0001]//Si[111] along the growth direction and ZnO[11math01]//GaN[11math0]//Si[1math0] along the in-plane direction. The successful growth of epitaxial ZnO/GaN films on Si demonstrates the feasibility and promise of integrating various functional devices on the same substrate. © 2001 American Institute of Physics.
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81.05.Dz II-VI semiconductors
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth

Simulation of the transformation from the C49 to the C54 phase of TiSi2 in blanket films and narrow conductors

S. Privitera, C. Spinella, F. La Via, M. G. Grimaldi, and E. Rimini

Appl. Phys. Lett. 78, 1514 (2001); http://dx.doi.org/10.1063/1.1354669 (3 pages) | Cited 2 times

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The C49–C54 phase transition has been simulated by Monte–Carlo calculations in blanket films and conductors using a unitary model based on transient nucleation and growth which takes into account the temperature dependence of the nucleation parameters. The output of the model has been compared with experimental data from electrical measurements in blanket films and 0.5 μm wide conductors. The comparison allows us to determine the density of available nucleation sites and to interpret the spread of experimental data, observed in the case of lines, as fluctuations in the number of sites and in their random location. © 2001 American Institute of Physics.
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64.70.K- Solid-solid transitions
64.60.Q- Nucleation
68.55.A- Nucleation and growth
85.40.Ls Metallization, contacts, interconnects; device isolation
02.70.Uu Applications of Monte Carlo methods
73.61.At Metal and metallic alloys

Study of ultrathin Al2O3/Si(001) interfaces by using scanning reflection electron microscopy and x-ray photoelectron spectroscopy

Manisha Kundu, Noriyuki Miyata, and Masakazu Ichikawa

Appl. Phys. Lett. 78, 1517 (2001); http://dx.doi.org/10.1063/1.1355294 (3 pages) | Cited 27 times

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Al2O3/Si(001) interfaces were investigated using scanning reflection electron microscopy and x-ray photoelectron spectroscopy. A uniform and stoichiometric ultrathin Al2O3 film of ∼0.6 nm was grown on an atomically flat Si(001)-2×1 surface, and the resulting Al2O3/Si(001) interface was atomically abrupt. Furthermore, an intentional high-pressure oxidation shows that we can grow Si oxide at the Al2O3/Si(001) interface with atomic-scale uniformity as this oxidation proceeds in a layer-by-layer manner. The resulting Si oxide/Si(001) interface was also atomically abrupt. In addition, the rate of oxidation of Si at the Al2O3/Si(001) interface depends strongly on the O2 pressure. © 2001 American Institute of Physics.
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68.35.Ct Interface structure and roughness
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Xy Scanning Auger microscopy, photoelectron microscopy
81.65.Mq Oxidation
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
79.60.Jv Interfaces; heterostructures; nanostructures

Atomic resolution structure of growth and etching patterns at the surface of microwave plasma chemical vapor deposited diamond films

P. B. Lukins, M. H. Zareie, and J. Khachan

Appl. Phys. Lett. 78, 1520 (2001); http://dx.doi.org/10.1063/1.1352046 (3 pages) | Cited 3 times

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Scanning tunneling microscopy and spectroscopy of microwave chemical vapor deposited diamond films prepared using a methane/hydrogen gas mixture indicates that the predominant diamond surface structure is (001) 1×1: 2H with a wide variety of facet shapes and orientations, and that the film surface is diamond-like and semiconductive but with a surface band gap (∼1.1 eV) that is smaller than the band gap of normal bulk diamond. Significant differences are observed in the electronic properties, resolution, and contrast between newly deposited surface carbon atoms and those bound in the underlying lattice. The composition of the deposition gas mixture is important in determining both the crystal structure and the type of bond termination at the surface. © 2001 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
81.05.U- Carbon/carbon-based materials
68.55.A- Nucleation and growth
81.05.Cy Elemental semiconductors
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Dq Plasma-based ion implantation and deposition
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
73.20.At Surface states, band structure, electron density of states

Magneto-optical properties of a GaAs:MnAs hybrid structure sandwiched by GaAs/AlAs distributed Bragg reflectors: Enhanced magneto-optical effect and theoretical analysis

H. Shimizu, M. Miyamura, and M. Tanaka

Appl. Phys. Lett. 78, 1523 (2001); http://dx.doi.org/10.1063/1.1354657 (3 pages) | Cited 27 times

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We have fabricated a multilayer structure consisting of a semiconductor-magnetic hybrid material GaAs:MnAs and GaAs/AlAs distributed Bragg reflectors, that is a one-dimensional semiconductor-based magnetophotonic crystal. Significant enhancement of magneto-optical effect was demonstrated at a controlled wavelength at room temperature. Magneto-optical spectra of this multilayer system were well explained by theoretical calculations, and the mechanism for the enhancement of magneto-optical effect was shown. Also, the required conditions for application to optical isolators are discussed and some potential solutions are indicated. Since our structure is composed of all semiconductor-based materials, the present results potentially lead to semiconductor based magneto-optical devices integrated with III–V-based optoelectronics. © 2001 American Institute of Physics.
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78.20.Ls Magneto-optical effects
85.70.Sq Magnetooptical devices
42.79.Wc Optical coatings
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.30.Fs III-V and II-VI semiconductors
75.50.Pp Magnetic semiconductors

Strain and composition dependence of the E1(TO) mode in hexagonal Al1−xInxN thin films

A. Kasic, M. Schubert, J. Off, and F. Scholz

Appl. Phys. Lett. 78, 1526 (2001); http://dx.doi.org/10.1063/1.1355010 (3 pages) | Cited 15 times

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Infrared spectroscopic ellipsometry is used to study the influence of strain and composition on the transverse-optical phonon mode of E1 symmetry in hexagonal Al1−xInxN films for 0.12 ⩽ x ⩽ 0.21. The 0.1–0.2-μm thick films were grown on slightly compressively strained hexagonal GaN buffer layers, or directly on [0001] sapphire by metalorganic vapor phase epitaxy. The Al1−xInxN E1(TO) phonon shows a one-mode behavior in contrast to recent theoretical predictions [H. Grille, C. Schnittler, and F. Bechstedt, Phys. Rev. B 61, 6091 (2000)]. Films grown on GaN reveal the influence of strain on the phonon mode frequencies due to pseudomorphic film growth. Al1−xInxN deposited directly on sapphire possesses phonon modes which indicate fully relaxed film growth. © 2001 American Institute of Physics.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
68.55.Nq Composition and phase identification
68.60.Bs Mechanical and acoustical properties

V-shaped defects connected to inversion domains in AlGaN layers

B. Pécz, Zs. Makkai, M. A. di Forte-Poisson, F. Huet, and R. E. Dunin-Borkowski

Appl. Phys. Lett. 78, 1529 (2001); http://dx.doi.org/10.1063/1.1355996 (3 pages) | Cited 18 times

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Thick AlGaN layers and AlGaN/GaN superlattices have been grown on GaN using metalorganic chemical vapor deposition. Cross-sectional transmission electron microscopy has been used to show that V-shaped surface pits on these samples differ from similar features observed in the InGaN system. Inversion domains and segregated Al are found in the middle of each V pit, and superlattice layers are observed to follow the pit sidewalls. © 2001 American Institute of Physics.
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68.65.Cd Superlattices
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Spontaneous formation of horizontal chevrons in smectic-C∗ liquid crystals

G. Strangi, D. A. Coleman, J. E. Maclennan, M. Copic, and N. A. Clark

Appl. Phys. Lett. 78, 1532 (2001); http://dx.doi.org/10.1063/1.1352661 (3 pages) | Cited 3 times

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We report an unusual structural formation observed in surface-stabilized ferroelectric liquid crystal cells with asymmetrically treated surfaces of 3-Glycidoxypropyl trimethoxysilane and nylon. On cooling the material W415 from the smectic-A∗ to the smectic-C∗ phase, the bookshelf smectic layers spontaneously rearrange to form a horizontal chevron structure, manifested optically as a periodic texture of uniform stripes. The polarization is perpendicular to the boundary plates and reverses direction from stripe to stripe, while the director is oriented in the plane of the cell and alternates symmetrically about the stripe direction. In an applied field the cells show a V-shaped (analog) electro-optic response. © 2001 American Institute of Physics.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
42.70.Df Liquid crystals
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
78.20.Jq Electro-optical effects
77.22.Ej Polarization and depolarization
77.80.Fm Switching phenomena

Co cluster coalescence behavior observed by electrical conduction and transmission electron microscopy

D. L. Peng, T. J. Konno, K. Wakoh, T. Hihara, and K. Sumiyama

Appl. Phys. Lett. 78, 1535 (2001); http://dx.doi.org/10.1063/1.1354158 (3 pages) | Cited 13 times

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We deposited monodispersed Co clusters with mean diameters d = 6, 8.5, and 13 nm on quartz and microgrid substrates using a plasma-gas-condensation-type cluster beam deposition system. The cluster–cluster coalescence behavior of the Co cluster assemblies was investigated by in situ electrical conductivity measurements and ex situ transmission electron microscopy (TEM). The electrical conductivity measurement indicates that, below temperature T ≈ 100 °C, the Co clusters with d = 8.5 nm maintain their original size as deposited at room temperature, while the cluster–cluster coalescence takes place at their interface at T>100 °C. The TEM observation indicates that the morphology of the cluster distribution shows no marked change at substrate temperatures Ts<250 °C. Above Ts = 300 °C, the interfacial area of coalesced clusters is crystalline, and has its own orientation, different from that of two connected cluster cores. © 2001 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
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