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4 Oct 2004

Volume 85, Issue 14, pp. 2679-2983

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 2860 (2004); http://dx.doi.org/10.1063/1.1799245 (3 pages)

Priya Mahadevan and Alex Zunger
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Valence photoelectron spectra of an electron-beam-irradiated C60 film

Jun Onoe, Aiko Nakao, and Akira Hida

Appl. Phys. Lett. 85, 2741 (2004); http://dx.doi.org/10.1063/1.1799229 (3 pages) | Cited 10 times

Online Publication Date: 14 October 2004

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Valence photoelectron spectra of an electron-beam (EB) irradiated C60 film, which exhibited metallic electron-transport properties in air at room temperature, are presented. The electronic structure of the C60 film became closer to that of graphite as the EB-irradiation time increased, and its density of states around the Fermi level was eventually greater than for the graphite. This suggests that the electronic structure of the C60 film changed from a semiconductor to a semimetal and/or metal by EB irradiation. Interestingly, the electronic structure remained metallic even after five days of air exposure, which is the reason for the metallic electron-transport property in our previous report [Appl. Phys. Lett. 82, 595 (2003)].
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79.60.Dp Adsorbed layers and thin films
71.20.Tx Fullerenes and related materials; intercalation compounds
61.80.Fe Electron and positron radiation effects
81.05.ub Fullerenes and related materials

Thin biaxially textured TiN films on amorphous substrates prepared by ion-beam assisted pulsed laser deposition

R. Hühne, S. Fähler, and B. Holzapfel

Appl. Phys. Lett. 85, 2744 (2004); http://dx.doi.org/10.1063/1.1802385 (3 pages) | Cited 11 times

Online Publication Date: 14 October 2004

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Thin TiN films have been grown using reactive ion-beam assisted pulsed laser deposition. The texture development was in situ analyzed using reflection high-energy electron diffraction. Above 300 °C a sharp cube textured nucleation layer is observed using an ion beam with energies above 400 eV under an angle of 45° relative to the substrate normal. The cube texture is not stable during further ion-beam assisted growth but can be preserved using homoepitaxial growth. Resulting films showed an in-plane orientation of about 13°. The texture development can be described in terms of energy considerations and anisotropic sputter rates.
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68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.Fg Pulsed laser ablation deposition
81.15.Jj Ion and electron beam-assisted deposition; ion plating

Photomechanical effect in films of polyvinylidene fluoride

Sergey S. Sarkisov, Michael J. Curley, Aisha Fields, Sergey S. Sarkisov, and Grigory Adamovsky

Appl. Phys. Lett. 85, 2747 (2004); http://dx.doi.org/10.1063/1.1802390 (3 pages) | Cited 5 times

Online Publication Date: 14 October 2004

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Photothermal bending of strips of polyvinylidene fluoride was initiated by a laser beam with a power of a few milliwatts. A bending strip generated a force of 10−4 N that propelled a 1 g oscillating wheel of a mechanical clock. The frequency of photomechanical resonance at pulsed illumination was inversely proportional to the length of the strip. The proposed model explained bending as a result of uneven thermal expansion on opposite sides of the strip. The model predicted, in agreement with experiment, that the force is proportional to beam power and does not depend on the shape or position of the beam in the strip.
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78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
65.40.De Thermal expansion; thermomechanical effects

On the origin of ultrahigh cryogenic strength of nanocrystalline metals

Y. M. Wang and E. Ma

Appl. Phys. Lett. 85, 2750 (2004); http://dx.doi.org/10.1063/1.1799238 (3 pages) | Cited 66 times

Online Publication Date: 14 October 2004

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At liquid nitrogen temperature, the yield strength of nanocrystalline Ni and Co increases by as much as 50%–80% over the already-impressive (∼1 GPa) room-temperature values. This unusual strength ratio as well as the remarkable magnitude of flow stress reached (as high as 2.5 GPa) are unexpected for conventional close-packed pure metals. The strong temperature dependence is attributed to the unusually small activation volume measured in strain rate change tests. Grain boundary dislocation nucleation is proposed as the thermally activated deformation mechanism in nanocrystalline grains.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.46.-w Structure of nanoscale materials

Improvement of the uniformity of self-assembled InAs quantum dots grown on InGaAs∕GaAs by low-pressure metalorganic chemical vapor deposition

Tao Yang, Shiro Tsukamoto, Jun Tatebayashi, Masao Nishioka, and Yasuhiko Arakawa

Appl. Phys. Lett. 85, 2753 (2004); http://dx.doi.org/10.1063/1.1802376 (3 pages) | Cited 8 times

Online Publication Date: 14 October 2004

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We report an approach to improve the uniformity of self-assembled InAs quantum dots (QDs) grown on a strained In0.12Ga0.88As buffer layer on GaAs substrates by low-pressure metalorganic chemical vapor deposition. By inserting a thin GaAs layer between the InAs QD layer and the In0.12Ga0.88As buffer layer and examining its thickness effect, we demonstrate that the photoluminescence (PL) inhomogeneous linewidth from the QDs can be improved by increasing the thickness of the thin GaAs layer. The PL inhomogeneous linewidth is significantly decreased from about 70 to 20 meV at 7 K as the thickness is increased from 0 to 2 nm. This significant improvement of the PL inhomogeneous linewidth is due to the fact that the QDs change from a bimodal distribution to a monomodal distribution consisting only of large QDs as a result of the inserted thin GaAs layer.
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81.05.Ea III-V semiconductors
81.07.Ta Quantum dots
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Hydrogen diffusion and interpretation of the 200 K anelastic relaxation in NiTi alloys

F. M. Mazzolai, B. Coluzzi, G. Mazzolai, and A. Biscarini

Appl. Phys. Lett. 85, 2756 (2004); http://dx.doi.org/10.1063/1.1799247 (3 pages) | Cited 13 times

Online Publication Date: 14 October 2004

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The internal friction, the Young’s modulus, and the heat flow have been measured as a function of temperature (20–360 K) at kilohertz frequencies in a H-free and H-doped Ni50.8Ti49.2 alloy, solubilized under vacuum and rapidly furnace cooled. The chemical H-diffusion coefficient DC has been deduced from absorption experiments (323–1063 K) and has been compared with the Einstein diffusion coefficient DE derived from a Snoek (or Zener)-type relaxation PH. The comparison has allowed the interpretation of the so-called 200 K relaxation as a Snoek (or Zener)-type relaxation due to hydrogen.
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62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
66.30.J- Diffusion of impurities
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
68.43.Mn Adsorption kinetics

Phase transition dynamics measurements in superheated liquids by monitoring the ejection of nanometer-thick films

Florian Lang, Paul Leiderer, and Savas Georgiou

Appl. Phys. Lett. 85, 2759 (2004); http://dx.doi.org/10.1063/1.1803618 (3 pages) | Cited 8 times

Online Publication Date: 14 October 2004

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The ejection dynamics of nanometer-thick liquid (isopropanol) films from a substrate caused by a phase transition in a superheated layer at the interface are studied. A nanosecond laser pulse is used to heat the substrate and as a result of heat transfer the fluid adjacent to the surface partially reaches a metastable state. Reflectivity and scattered light measurements demonstrate that the liquid is ejected as an intact layer which redeposits on the time scale of a few hundred nanoseconds. Measurements of the ejection dynamics are shown to be a sensitive method to obtain information about the phase transition, such as the relevant time scales and the generated pressure.
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68.15.+e Liquid thin films
64.70.F- Liquid-vapor transitions
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.20.Ek Optical activity
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Low-temperature bonding of silicon-oxide-covered wafers using diluted HF etching

Q.-Y. Tong, Q. Gan, G. Fountain, G. Hudson, and P. Enquist

Appl. Phys. Lett. 85, 2762 (2004); http://dx.doi.org/10.1063/1.1800275 (3 pages) | Cited 2 times

Online Publication Date: 14 October 2004

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For bonded pairs of silicon-oxide-covered wafers, the bonding energy at low temperatures is significantly enhanced by very slight etching of the silicon oxide surfaces in diluted (0.05%–0.2%) HF aqueous solutions prior to room temperature contacting. The bonding energy is a factor of 10 higher than standard bonded pairs to about 2000 mJ∕m2 after annealing at 100°C. The improved surface cleaning and activation with desired surface termination have been achieved by the HF dip. A fluorine concentration peak at the bonding interface measured by secondary ion mass spectroscopy suggests that the number of Si–O–Si covalent bonds at the bonding interface appears to be increased appreciably by the formation of fluorinated silicon oxide that absorbs water effectively.
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81.65.Cf Surface cleaning, etching, patterning
61.72.Cc Kinetics of defect formation and annealing
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Crystalline quality of bonded silicon-on-insulator characterized by spectroscopic ellipsometry and Raman spectroscopy

N. V. Nguyen, J. E. Maslar, Jin-Yong Kim, Jin-Ping Han, Jin-Won Park, D. Chandler-Horowitz, and E. M. Vogel

Appl. Phys. Lett. 85, 2765 (2004); http://dx.doi.org/10.1063/1.1800277 (3 pages) | Cited 2 times

Online Publication Date: 14 October 2004

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The crystalline quality of silicon-on-insulator fabricated by a wafer bonding technique was examined by spectroscopic ellipsometry and Raman spectroscopy. The detailed modeling of the experimental ellipsometric data yields information about structural defects in the silicon-on-insulator layer. The dielectric function of the silicon on insulator that best models the experimental ellipsometric data includes a physical mixture of crystalline silicon and about 4%–7% of amorphous silicon, suggesting a slight lack of long-range order of the silicon atoms in the silicon-on-insulator layer. The use of a dielectric function other than that of pure crystalline silicon is supported by Raman spectroscopic results that indicate the presence of structural defects in the silicon-on-insulator layer. These structural defects may be due to the effects of hydrogen implantation used in the fabrication process of silicon-on-insulator, and∕or the strain imposed by the lattice mismatch between the buried layer and the silicon substrate, and subsequently relaxed under high-temperature annealing.
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78.30.Hv Other nonmetallic inorganics
78.66.Db Elemental semiconductors and insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.Cc Kinetics of defect formation and annealing

Type of dissociated misfit dislocation in perovskite films on LaAlO3

C. J. Lu

Appl. Phys. Lett. 85, 2768 (2004); http://dx.doi.org/10.1063/1.1800289 (3 pages) | Cited 5 times

Online Publication Date: 14 October 2004

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A type of dissociated misfit dislocation in epitaxial Ba0.3Sr0.7TiO3 thin films on (001) LaAlO3 substrates has been studied by high-resolution transmission electron microscopy. The dislocation has a Burgers vector [210] and is dissociated into four partial dislocations with Burgers vectors of type ½〈110〉. All partials can relieve the localized misfit strain and they are interacted with three ½〈110〉 stacking faults lying on (001). The partials were generated during island nucleation and mosaic growth of the BSTO film, while a small amount of excess TiO2 during film deposition favored the formation of the ½〈110〉 stacking faults.
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68.55.A- Nucleation and growth
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Nn Stacking faults and other planar or extended defects
81.15.Fg Pulsed laser ablation deposition
68.37.Lp Transmission electron microscopy (TEM)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Formation of columnar (In,Ga)As quantum dots on GaAs(100)

J. He, R. Nötzel, P. Offermans, P. M. Koenraad, Q. Gong, G. J. Hamhuis, T. J. Eijkemans, and J. H. Wolter

Appl. Phys. Lett. 85, 2771 (2004); http://dx.doi.org/10.1063/1.1801172 (3 pages) | Cited 31 times

Online Publication Date: 14 October 2004

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Columnar (In,Ga)As quantum dots (QDs) with homogeneous composition and shape in the growth direction are realized by molecular-beam epitaxy on GaAs(100) substrates. The columnar (In,Ga)As QDs are formed on InAs seed QDs by alternating deposition of thin GaAs intermediate layers and monolayers of InAs with extended growth interruptions after each layer. The height of the columnar (In,Ga)As QDs is controlled by varying the number of stacked GaAs∕InAs layers. The structural and optical properties are studied by cross-sectional scanning tunneling microscopy, atomic force microscopy, and photoluminescence spectroscopy. With increase of the aspect ratio of the columnar QDs, the emission wavelength is redshifted and the linewidth is reduced.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
78.55.Cr III-V semiconductors
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
78.66.Fd III-V semiconductors
78.67.Hc Quantum dots
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Origins of luminescence from nitrogen-ion-implanted epitaxial GaAs

X. Weng, R. S. Goldman, V. Rotberg, N. Bataiev, and L. J. Brillson

Appl. Phys. Lett. 85, 2774 (2004); http://dx.doi.org/10.1063/1.1803940 (3 pages) | Cited 4 times

Online Publication Date: 14 October 2004

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We have examined the origins of luminescence in N-ion-implanted epitaxial GaAs, using a combination of cross-sectional transmission electron microscopy and low-energy electron-excited nanoscale-luminescence spectroscopy. A comparison of reference, as-implanted, and implanted-plus-annealed samples reveals a variety of emissions. In all samples, we observe the GaAs fundamental band-gap emission, as well as several emissions related to GaAs native defects. In the as-implanted and implanted-plus-annealed samples, an emission related to the implantation-induced defects, is also observed. Interestingly, in the implanted-plus-annealed samples, we identify a near-infrared emission associated with GaAsN nanocrystallites.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.37.Lp Transmission electron microscopy (TEM)

Long-range order in a multilayer organic film templated by a molecular-induced surface reconstruction: Pentacene on Au(110)

Ph. Guaino, D. Carty, G. Hughes, O. McDonald, and A. A. Cafolla

Appl. Phys. Lett. 85, 2777 (2004); http://dx.doi.org/10.1063/1.1786655 (3 pages) | Cited 22 times

Online Publication Date: 14 October 2004

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We describe the growth of a highly ordered pentacene film on the Au(110) surface, investigated in both real and reciprocal space using scanning tunneling microscopy and low-energy electron diffraction techniques. At high coverage, a unidirectional multilayer of π-stacked molecular row is formed with long-range order. Investigations of the interface at low molecular coverage show that this molecular arrangement is a direct consequence of a pentacene-induced surface reconstruction. Pentacene molecules initially adsorb between atomic gold rows of the Au(110)–(1×2) missing row structure and induce a (1×3) surface reconstruction, acting as a template for the organic film formation.
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68.55.A- Nucleation and growth
68.65.Ac Multilayers
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.43.Mn Adsorption kinetics
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

High friction of a vertically aligned carbon-nanotube film in microtribology

Hiroshi Kinoshita, Ippei Kume, Masahito Tagawa, and Nobuo Ohmae

Appl. Phys. Lett. 85, 2780 (2004); http://dx.doi.org/10.1063/1.1804254 (2 pages) | Cited 15 times

Online Publication Date: 14 October 2004

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The frictional behavior of a vertically aligned carbon-nanotube (VACNT) film against gold tips was studied in air. In these experiments, the film was 6 μm thick, the tip radii 4.5–30 μm, the applied forces smaller than 5 μN, and speeds were 0.15–24 μm/s. In spite of the null adhesion force to the gold tip, extremely high friction coefficients of 1.0–2.2 were found for the VACNT film. No dependence of friction on speed or tip radius was observed.
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81.05.ub Fullerenes and related materials
81.40.Pq Friction, lubrication, and wear
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.Qp Friction, tribology, and hardness
62.20.F- Deformation and plasticity
68.35.Np Adhesion

Thermoelectric PbTe thin film for superresolution optical data storage

Hyun Seok Lee, Byung-ki Cheong, Taek Sung Lee, Kyeong Seok Lee, Won Mok Kim, Jae Won Lee, Sung Ho Cho, and Joo Youl Huh

Appl. Phys. Lett. 85, 2782 (2004); http://dx.doi.org/10.1063/1.1801684 (3 pages) | Cited 11 times

Online Publication Date: 14 October 2004

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To find its practical use in ultrahigh density optical data storage, superresolution (SR) technique needs a material that can render a high SR capability at no cost of durability against repeated readout and write. Thermoelectric materials appear to be promising candidates due to their capability of yielding phase-change-free thermo-optic changes. A feasibility study was carried out with PbTe for its large thermoelectric coefficient and high stability over a wide temperature range as a crystalline single phase. Under exposure to pulsed red light, the material was found to display positive, yet completely reversible changes of optical transmittance regardless of laser power, fulfilling basic requirements for SR readout and write. The material was also shown to have a high endurance against repeated static laser heating of up to 106–107 cycles tested. A read only memory disk with a PbTe SR layer led to the carrier to noise ratio value of 47 dB at 3.5 mW for 0.25 μm pit; below the optical resolution limit (∼0.27 μm) of the tester.
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42.79.Vb Optical storage systems, optical disks
68.55.-a Thin film structure and morphology
61.82.Fk Semiconductors
72.20.Pa Thermoelectric and thermomagnetic effects
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects

Evaluation of the internal field in lithium niobate ferroelectric domains by an interferometric method

M. de Angelis, S. De Nicola, A. Finizio, G. Pierattini, P. Ferraro, S. Grilli, and M. Paturzo

Appl. Phys. Lett. 85, 2785 (2004); http://dx.doi.org/10.1063/1.1797534 (3 pages) | Cited 17 times

Online Publication Date: 14 October 2004

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We report on the evaluation of internal electric field of a ferroelectric engineered-domain in a LiNbO3 wafer crystal by detecting optical path length variation with a noninvasive interferometric inspection method. The lithium niobate wafer has been patterned and subjected to electric field poling to obtain two antiparallel ferroelectric domains separated by a single domain wall. The crystal has been mounted into one arm of a Mach–Zehnder-type interferometer to study the phase map and evaluate the effects of domain reversion by a digital holographic technique. Evaluation of the internal field and consequent variation of the electro-optical properties of the different domains is analyzed.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
42.70.Mp Nonlinear optical crystals
77.80.Dj Domain structure; hysteresis
78.20.Jq Electro-optical effects
42.40.Kw Holographic interferometry; other holographic techniques

The microprocesses of the quasicrystalline transformation in Zr65Ni10Cu7.5Al7.5Ag10 bulk metallic glass

L. Liu, K. C. Chan, and G. K. H. Pang

Appl. Phys. Lett. 85, 2788 (2004); http://dx.doi.org/10.1063/1.1801677 (3 pages) | Cited 3 times

Online Publication Date: 14 October 2004

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The microprocesses of the amorphous-to-quasicrystalline transformation in Zr65Ni10Cu7.5Al7.5Ag10 bulk metallic glass were studied in detail by transmission electron microscopy (TEM) and high-resolution TEM (HRTEM). It was found that the amorphous-to-quasicrystalline transformation in the present system undergoes a series of interprocesses and follows the sequence of the phase transformation of amorphous →FCC Zr2Ni→Tetragonal Zr2Ni→Tetragonal Zr2Ni with a domain structure →Quasicrystals. HRTEM indicated that a domain structure with a high density of stacking faults was formed in the sample at the stage just prior to the formation of quasicrystals. This special structure seems to possess the structural symmetries similar to those of icosahedral quasicrystals. Nanobeam energy dispersive x-ray spectrum revealed that atomic diffusion was involved in all interprocesses of the phase transformations. This suggests that the amorphous-to-quasicrystalline transformation in the present bulk metallic glass is a nonpolymorphous reaction.
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61.43.Fs Glasses
61.44.Br Quasicrystals
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
81.05.Kf Glasses (including metallic glasses)
64.70.K- Solid-solid transitions
68.37.Lp Transmission electron microscopy (TEM)
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Quantum-confined Stark effect and built-in dipole moment in self-assembled InAs∕GaAs quantum dots

Peng Jin, C. M. Li, Z. Y. Zhang, F. Q. Liu, Y. H. Chen, X. L. Ye, B. Xu, and Z. G. Wang

Appl. Phys. Lett. 85, 2791 (2004); http://dx.doi.org/10.1063/1.1801678 (3 pages) | Cited 12 times

Online Publication Date: 14 October 2004

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Quantum-confined Stark effect and built-in dipole moment in self-assembled InAs∕GaAs quantum dots (QDs), which are grown at relative low temperature (460°C) and embedded in GaAs p–i–n structure, have been studied by dc-biased electroreflectance. Franz–Keldysh oscillations from the undoped GaAs layer are used to determine the electric field under various bias voltages. Stark shift of −34 meV for the ground-state interband transition of the QDs is observed when the electric field increases from 105 to 308 kV∕cm. The separation of the electron and hole states in the growth direction of 0.4 nm, corresponding to the built-in dipole moment of 6.4×10−29 C m, is determined. It is found that the electron state lies above that of the hole, which is the same as that predicted by theoretical calculations for ideal pyramidal InAs QDs.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
73.21.La Quantum dots
78.67.Hc Quantum dots
78.66.Fd III-V semiconductors
78.20.Jq Electro-optical effects
71.20.Nr Semiconductor compounds
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Np Solid phase epitaxy; growth from solid phases

Molecular beam epitaxial growth and characterization of zinc-blende ZnMgSe on InP (001)

Mohammad Sohel, Martin Muñoz, and Maria C. Tamargo

Appl. Phys. Lett. 85, 2794 (2004); http://dx.doi.org/10.1063/1.1804611 (3 pages) | Cited 7 times

Online Publication Date: 14 October 2004

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High crystalline quality zinc-blende structure Zn(1−x)MgxSe epitaxial layers were grown on InP (001) substrates by molecular beam epitaxy. Their band gap energies were determined as a function of Mg concentration and a linear dependence was observed. The band gap of the Zn(1−x)MgxSe closely lattice matched to InP was found to be 3.59 eV at 77 K and the extrapolated value for zinc-blende MgSe was determined to be 3.74 eV. Quantum wells of Zn(1−x)CdxSe with Zn(1−x)MgxSe as the barrier layer were grown which exhibit near ultraviolet emission.
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81.05.Dz II-VI semiconductors
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

High-reflectivity Pd∕Ni∕Al∕Ti∕Au ohmic contacts to p-type GaN for ultraviolet light-emitting diodes

Guan-Ting Chen, Chang-Chi Pan, Chi-Shin Fang, Tzu-Chien Huang, Jen-Inn Chyi, Mao-Nan Chang, Sheng-Bang Huang, and Jung-Tsung Hsu

Appl. Phys. Lett. 85, 2797 (2004); http://dx.doi.org/10.1063/1.1805199 (3 pages) | Cited 9 times

Online Publication Date: 14 October 2004

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Thermal stability, optical reflectivity, and contact resistivity of Pd∕Ni∕Al∕Ti∕Au ohmic contacts to p-type GaN were investigated. In contrast to its Pd∕Al∕Ti∕Au counterparts, Pd∕Ni∕Al∕Ti∕Au contacts retained their specific contact resistivity (<2×10−2 Ω cm2) and reflectivity (>76%) after long-term annealing at 150 °C in nitrogen ambient. According to the results of the secondary ion mass spectroscopy study, it is suggested that the Ni layer prevents the penetration of Ti into GaN during thermal treatment.
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73.40.Ns Metal-nonmetal contacts
85.60.Jb Light-emitting devices
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
78.40.Kc Metals, semimetals, and alloys
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Exact electroelastic solutions for penny-shaped cracks under prescribed temperature or thermal flow

B. L. Wang

Appl. Phys. Lett. 85, 2800 (2004); http://dx.doi.org/10.1063/1.1789579 (3 pages) | Cited 4 times

Online Publication Date: 14 October 2004

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This letter provides an exact solution for a thermal penny-shaped crack in piezoelectric media. An arbitrarily distributed temperature field applied on the crack faces is considered first. Closed-form expressions for the stress and electric displacement intensity factors at the crack border are given. Electrically impermeable cracks, electrically permeable cracks, and the permittivity of the medium inside the cracks are considered. Then, crack tip field intensity factors for a prescribed thermal flow on the crack faces are obtained. The solutions are mainly provided for transversely isotropic materials, but results for isotropic materials and dielectrics are also given.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
77.65.Ly Strain-induced piezoelectric fields
46.50.+a Fracture mechanics, fatigue and cracks

Highly photoconductive amorphous carbon nitride films prepared by cyclic nitrogen radical sputtering

T. Katsuno, S. Nitta, H. Habuchi, V. Stolojan, and S. R. P. Silva

Appl. Phys. Lett. 85, 2803 (2004); http://dx.doi.org/10.1063/1.1792384 (3 pages) | Cited 15 times

Online Publication Date: 14 October 2004

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We report on the growth of amorphous carbon nitride films (a-CNx) showing the highest conductivity to date. The films were prepared using a layer-by-layer method (a-CNx:LL), by the cyclical nitrogen radical sputtering of a graphite radical, alternated with a brief hydrogen etch. The photosensitivity S of these films is 105, defined as the ratio of the photoconductivity σp to the dark conductivity σd and is the highest value reported thus far. We believe that the carriers generated by the monochromatic light (photon energy 6.2 eV) in the a-CNx:LL films are primarily electrons, with the photoconductivity shown to increase with substrate deposition temperature.
Show PACS
68.55.A- Nucleation and growth
73.50.Pz Photoconduction and photovoltaic effects
73.61.Ng Insulators
81.15.Cd Deposition by sputtering
81.65.Cf Surface cleaning, etching, patterning
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