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3 Oct 2005

Volume 87, Issue 14, Articles (14xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 87, 143902 (2005); http://dx.doi.org/10.1063/1.2077839 (3 pages)

Kaustubh D. Bhalerao, Edward Eteshola, Matthew Keener, and Stephen C. Lee
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Microcavity plasma photodetectors: Photosensitivity, dynamic range, and the plasma-semiconductor interface

N. P. Ostrom and J. G. Eden

Appl. Phys. Lett. 87, 141101 (2005); http://dx.doi.org/10.1063/1.2072767 (3 pages) | Cited 8 times

Online Publication Date: 26 September 2005

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Detailed measurements of the photosensitivity of Si microcavity plasma photodetectors in the visible and near-infrared (420–1100 nm) are reported for input optical intensities to a 100×100 μm2 inverted pyramid device varied over three orders of magnitude (10−5–10−2 W cm−2). By resolving the contribution to the overall device response from the plasma/semiconductor interaction, as opposed to bulk Si photoconductivity, the photosensitivity of the plasma photodetector operating in 500 Torr of Ne was determined to range from (2.2±0.4) A/W for 2 nW of input power (at λ = 780 nm) to (1.3±0.2) A/W at ∼ 0.65 μW. The spectral response profile of the hybrid plasma/semiconductor detector is similar to that of a conventional pn junction photodiode, but is blueshifted by ∼ 60 nm. Also, the peak photosensitivity (3.5 A/W at λ ≃ 900 nm) of a Si microplasma device having a 50×50 μm2 aperture is approximately twice that for its larger (100×100 μm2) counterpart under identical conditions. Analysis of the data suggest that bandbending at the p-Si surface is sufficiently strong for a thin n-type region to form, thereby resembling a metal-oxide-semiconductor capacitor in the inversion mode. Electrons in this thin layer tunnel through the vacuum (Si-plasma) barrier, followed by electron avalanche in the nonequilibrium plasma. These results illustrate the potential for novel optoelectronic devices when interfacing a plasma with a semiconductor and coupling the two media with a strong electric field imposed across the interface.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors

Effect of doping concentration on the performance of terahertz quantum-cascade lasers

H. C. Liu, M. Wächter, D. Ban, Z. R. Wasilewski, M. Buchanan, G. C. Aers, J. C. Cao, S. L. Feng, B. S. Williams, and Q. Hu

Appl. Phys. Lett. 87, 141102 (2005); http://dx.doi.org/10.1063/1.2067699 (3 pages) | Cited 34 times

Online Publication Date: 26 September 2005

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We characterized a set of terahertz quantum-cascade lasers with identical device parameters except for the doping concentration. The δ-doping density was varied from 3.2×1010 to 4.8×1010 cm−2. We observed that the threshold current density increased monotonically with doping. Moreover, the measured results on devices with different cavity lengths provided evidence that the free carrier absorption caused waveguide loss also increased monotonically. Interestingly, however, the observed maximum lasing temperature displayed an optimum at a doping density of 3.6×1010 cm−2.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
61.72.S- Impurities in crystals

Resonant-cavity-enhanced photodetectors for the mid-infrared

Martin Arnold, Dmitry Zimin, and Hans Zogg

Appl. Phys. Lett. 87, 141103 (2005); http://dx.doi.org/10.1063/1.2061855 (3 pages) | Cited 13 times

Online Publication Date: 27 September 2005

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High-efficiency resonant-cavity-enhanced photodetectors for the mid-wavelength infrared range have been realized. Spectral linewidths as narrow as 0.07 μm at 4.13 μm and 0.24 μm at 8.41 μm center wavelength, respectively, have been achieved. Peak quantum efficiencies are up to above 50%. The photovoltaic devices are based on IV-VI semiconductor layers grown epitaxially on Si substrates and employing a distributed Bragg mirror to form the cavity.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Influence of microdefects on the polarization properties of polymeric optical waveguides studied by polarized near-field scanning optical microscopy

Tadashi Mitsui

Appl. Phys. Lett. 87, 141104 (2005); http://dx.doi.org/10.1063/1.2084326 (3 pages)

Online Publication Date: 27 September 2005

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In the present study, the polarization properties of propagation light within a polymeric optical waveguide were characterized by means of a polarized guide-collection-mode near-field scanning optical microscopy (NSOM) technique, and changes in the polarization properties around an indentation were evaluated. When transverse magnetic polarized light enters a waveguide, the light intensity becomes greater on the near side of the indentation than on the far side, as measured by a linearly polarized component perpendicular to the direction of light propagation. The most probable cause of this phenomenon is microdefects generated by the printing of the indentation. The polarized NSOM technique is useful in searching for small defects or stresses within integrated photonic devices.
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42.79.Gn Optical waveguides and couplers
42.70.Jk Polymers and organics
07.79.Fc Near-field scanning optical microscopes
42.82.Et Waveguides, couplers, and arrays
62.20.M- Structural failure of materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure

Scanning a photonic crystal slab nanocavity by condensation of xenon

S. Mosor, J. Hendrickson, B. C. Richards, J. Sweet, G. Khitrova, H. M. Gibbs, T. Yoshie, A. Scherer, O. B. Shchekin, and D. G. Deppe

Appl. Phys. Lett. 87, 141105 (2005); http://dx.doi.org/10.1063/1.2076435 (3 pages) | Cited 59 times

Online Publication Date: 28 September 2005

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Allowing xenon or nitrogen gas to condense onto a photonic crystal slab nanocavity maintained at 10–20 K results in shifts of the nanocavity mode wavelength by as much as 5 nm ( ≅ 4 meV). This occurs in spite of the fact that the mode defect is achieved by omitting three holes to form the spacer. This technique should be useful in changing the detuning between a single quantum dot transition and the nanocavity mode for cavity quantum electrodynamics experiments, such as mapping out a strong coupling anticrossing curve. Compared with temperature scanning, it has a much larger scan range and avoids phonon broadening.
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42.50.Pq Cavity quantum electrodynamics; micromasers
42.55.Tv Photonic crystal lasers and coherent effects

F2-laser digital etching of colloidal photonic crystals

J. Li, P. R. Herman, V. Kitaev, S. Wong, and G. A. Ozin

Appl. Phys. Lett. 87, 141106 (2005); http://dx.doi.org/10.1063/1.2077857 (3 pages) | Cited 4 times

Online Publication Date: 28 September 2005

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We report on digital etching of silica colloidal photonic crystals by employing a pulsed deep-ultraviolet F2 laser at 157 nm wavelength. When the laser fluence is above a microsphere-size-dependent threshold and within an appropriate fluence window, colloidal crystals can be etched in a digitized fashion, whereby a single microsphere layer can be removed upon exposure to a single laser pulse. Alternatively, single spheres or lines of spheres can be selectively ejected by patterning the laser beam. The results demonstrate a fast, noncontact, straightforward, and cost-effective approach for engineering extrinsic defects into colloidal photonic crystals.
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42.70.Qs Photonic bandgap materials
81.65.Cf Surface cleaning, etching, patterning
82.70.Dd Colloids
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

InGaAs–AlInAs/InP terahertz quantum cascade laser

Lassaad Ajili, Giacomo Scalari, Nicolas Hoyler, Marcella Giovannini, and Jérôme Faist

Appl. Phys. Lett. 87, 141107 (2005); http://dx.doi.org/10.1063/1.2081122 (3 pages) | Cited 12 times

Online Publication Date: 28 September 2005

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Operation of a quantum-cascade laser based on the In0.52Al0.48As–In0.53Ga0.47As/InP material is demonstrated at a frequency of 3.6 terahertz. The active region is based on a bound-to-continuum transition combined with an optical phonon extraction. The optical waveguide exploits a combination of metallic and dielectric confinement. Threshold current density of 460 A/cm2 at 10 K and a maximum operating temperature of 45 K are achieved.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.79.Gn Optical waveguides and couplers

Model for two-beam coupling during the formation of holographic gratings with a nematic film-polymer-slice sequence structure

Roberto Caputo, Luciano De Sio, Alessandro Veltri, Cesare Umeton, and Andrey V. Sukhov

Appl. Phys. Lett. 87, 141108 (2005); http://dx.doi.org/10.1063/1.2048821 (3 pages) | Cited 3 times

Online Publication Date: 28 September 2005

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We present a model accounting for the main features of the wave coupling process that takes place during the UV curing of diffraction gratings made of liquid crystal films separated by slices of polymeric material. The effect depends on the phase shift between the curing interference pattern and the grating being cured. For a unit ratio of the impinging beam intensities, the model confirms the absence of energy transfer, as experimentally observed. When the ratio is not at its unit value, the beam coupling tends to equalize the intensities of the two beams as they propagate inside the sample.
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42.40.Eq Holographic optical elements; holographic gratings
42.79.Dj Gratings
42.70.Df Liquid crystals
42.70.Jk Polymers and organics
61.30.-v Liquid crystals

Design and simulation of InGaAs/AlAsSb quantum-cascade lasers for short wavelength emission

C. A. Evans, V. D. Jovanović, D. Indjin, Z. Ikonić, and P. Harrison

Appl. Phys. Lett. 87, 141109 (2005); http://dx.doi.org/10.1063/1.2067701 (3 pages) | Cited 4 times

Online Publication Date: 28 September 2005

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The design and simulation of an In0.53Ga0.47As/Al0.56As0.44Sb quantum-cascade laser emitting in the near infrared is presented. Designed using a self-consistent rate equation solver coupled with an energy balance rate equation, the proposed laser has a calculated population inversion of ∼ 20% at 77 K and sufficient gain to achieve room-temperature laser emission at λ ∼ 2.8 μm. Threshold currents in the range 4–8 kA/cm2 are estimated as the temperature increases from 77 K to 300 K. The output characteristics of the proposed laser are compared to an existing λ ∼ 3.1 μm In0.53Ga0.47As/Al0.56As0.44Sb quantum-cascade structure presented in the literature.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

45° polymer-based total internal reflection coupling mirrors for fully embedded intraboard guided wave optical interconnects

Li Wang, Xiaolong Wang, Wei Jiang, Jinho Choi, Hai Bi, and Ray Chen

Appl. Phys. Lett. 87, 141110 (2005); http://dx.doi.org/10.1063/1.2084331 (3 pages) | Cited 17 times

Online Publication Date: 30 September 2005

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An array of 50 μm×50 μm polymer waveguides with 45° total internal reflection (TIR) wideband coupling mirrors were fabricated by soft molding to achieve fully embedded boardlevel optoelectronic interconnects. The 45° TIR coupling mirrors were formed at the ends of the waveguides to provide surface normal light coupling between waveguides and optoelectronic devices. Three-dimensional optoelectronic interconnects were replicated in one-step transfer by the soft molding technique. The measured propagation loss of the multimode waveguide was 0.16 dB/cm at 850 nm wavelength. The coupling efficiency of the silver-coated 45° micromirrors buried under the top cladding was 92% with low polarization sensitivity.
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42.82.Ds Interconnects, including holographic interconnects
42.82.Et Waveguides, couplers, and arrays
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.79.Gn Optical waveguides and couplers
42.70.Jk Polymers and organics
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
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Influence of edge diffusion on the growth mode on vicinal surfaces

C. Ratsch, J. Garcia, and R. E. Caflisch

Appl. Phys. Lett. 87, 141901 (2005); http://dx.doi.org/10.1063/1.2077851 (3 pages) | Cited 3 times

Online Publication Date: 26 September 2005

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Growth on vicinal surfaces typically occurs via nucleation and growth of islands or via step flow. In this letter, we present computational results based on an island dynamics model that employs the level-set technique that study the transition between these two competing mechanisms. Our results demonstrate that the rate of diffusion of atoms along step edges is an additional parameter that controls the competition between these mechanisms. We make suggestions about how one might be able to exploit these results experimentally.
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81.15.Aa Theory and models of film growth
68.55.A- Nucleation and growth
66.30.Dn Theory of diffusion and ionic conduction in solids
68.35.Ct Interface structure and roughness

The strength of diamond

Mikhail I. Eremets, Ivan A. Trojan, Patience Gwaze, Joachim Huth, Reinhard Boehler, and Vladimir D. Blank

Appl. Phys. Lett. 87, 141902 (2005); http://dx.doi.org/10.1063/1.2061853 (3 pages) | Cited 22 times

Online Publication Date: 26 September 2005

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Diamond is the hardest known material; however, its mechanical stability, in particular the yield strength σy, is not known. We report reproducible generation of plastic deformation of diamond at room and low temperatures. We determined σy = 130–140 GPa by measuring the pressure distribution over the diamond anvils and by using the theory of elasticity. Yielding in diamond is accompanied by a strong luminescence with a characteristic spectrum. Our findings may be used to extend the static pressure limit beyond the current value of about 300 GPa(3 Megabars).
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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
62.20.D- Elasticity
78.55.Hx Other solid inorganic materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness

In situ transmission electron microscope observations of electromigration in copper lines at room temperature

C. N. Liao, K. C. Chen, W. W. Wu, and L. J. Chen

Appl. Phys. Lett. 87, 141903 (2005); http://dx.doi.org/10.1063/1.2081138 (3 pages) | Cited 12 times

Online Publication Date: 26 September 2005

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Atomic-scale electromigration (EM) in unpassivated copper metal lines was directly observed in ultrahigh vacuum at room temperature by transmission electron microscopy. It was found that copper atoms on a (211) crystal plane vanished directionally within half an hour when applying an electric current with a density of 2×106 A/cm2 through the tested Cu line. The EM-induced atomic migration appeared to be anisotropic, and the combination of {111} planes and ⟨110⟩ directions was suggested to be the easiest electromigration system for crystalline copper. EM-induced mass transport was also found to be responsible for the weakening (111) texture of the Cu lines after electric current stressing.
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66.30.Qa Electromigration
85.40.Ls Metallization, contacts, interconnects; device isolation
68.37.Lp Transmission electron microscopy (TEM)

Determination of crystallographic polarity of ZnO layers

H. Tampo, P. Fons, A. Yamada, K.-K. Kim, H. Shibata, K. Matsubara, S. Niki, H. Yoshikawa, and H. Kanie

Appl. Phys. Lett. 87, 141904 (2005); http://dx.doi.org/10.1063/1.2067689 (3 pages) | Cited 24 times

Online Publication Date: 26 September 2005

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The crystallographic polarity of ZnO epilayers was determined by x-ray diffraction (XRD) using anomalous dispersion near the Zn K edge. The method is not destructive and is straightforward to carry out using a typical XRD measurement system. The polarity difference between the Zn (0001) and O (000math) surfaces could be easily determined using a {0002} diffraction peak and the Bremstrahlung radiation from a Cu rotating anode source. By using the normalized pre- and post-Zn K-edge diffraction intensity ratios of the (0002) diffraction peak, Zn polar and O polar ZnO layers could always be distinguished but, the absolute value of the ratio was found to change with layer thickness. The absolute value of the ratio with layer thickness was found to have a linear dependence on layer thickness allowing determination of the polarity of (0001) ZnO epilayers with a single x-ray measurement and the known layer thickness in conjunction with standard data. Acid etching results confirmed the veracity of the polarity determination of the XRD measurement. To test the technique, Zn and O polar ZnO layers were grown by radical source molecular beam epitaxy (RS MBE) on MgO buffer layers on c-sapphire substrate and O polar ZnO layers were grown on a-plane substrates and measured using the x-ray technique with excellent agreement.
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68.55.-a Thin film structure and morphology
61.05.cp X-ray diffraction

Band-gap control optical Kerr effect and light self-focusing of semiconducting materials CdxHg1−xGa2S4

W.-D. Cheng, S.-P. Huang, D.-S. Wu, X.-D. Li, Y.-Z. Lan, F.-F. Li, J. Shen, H. Zhang, and Y.-J. Gong

Appl. Phys. Lett. 87, 141905 (2005); http://dx.doi.org/10.1063/1.2072787 (3 pages) | Cited 1 time

Online Publication Date: 26 September 2005

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We report the dispersion of the optical Kerr effect and the wavelength-dependent critical power of light self-focusing for semiconductors CdxHg1−xGa2S4 in view of the calculated results from the density functional theory combined with an anharmonic oscillator model. It is shown that the third-order optical properties are controlled by the band gaps or cation contents of CdxHg1−xGa2S4, and it is indicated that the optical Kerr effect decreases and the critical power of light self-focusing increases as the x contents and band gaps increase for CdxHg1−xGa2S4.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Bulk nanostructured alloys prepared by flux melting and melt solidification

T. D. Shen, R. B. Schwarz, and X. Zhang

Appl. Phys. Lett. 87, 141906 (2005); http://dx.doi.org/10.1063/1.2056610 (3 pages) | Cited 5 times

Online Publication Date: 26 September 2005

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We have prepared bulk nanostructured Ag60Cu40 alloys by a flux-melting and melt-solidification technique. The flux purifies the melts, leading to a large undercooling and nanometer-sized microstructure. The as-prepared alloys are composed of nanolayered Ag and Cu within micrometer-sized grains. The bulk nanostructured alloys have an ultimate tensile strength of approximately 560 MPa, similar yield strength in tension and compression, elongation of 7% in tension, strain hardening exponent of 0.1, and relatively high mechanical and thermal stability up to 400 °C.
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81.40.Lm Deformation, plasticity, and creep
81.05.Bx Metals, semimetals, and alloys
81.07.Bc Nanocrystalline materials
62.20.F- Deformation and plasticity
64.70.D- Solid-liquid transitions
61.46.-w Structure of nanoscale materials
81.30.Fb Solidification

Dual layer selective emitter

Donald L. Chubb and David S. Wolford

Appl. Phys. Lett. 87, 141907 (2005); http://dx.doi.org/10.1063/1.2077853 (3 pages) | Cited 2 times

Online Publication Date: 28 September 2005

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A selective emitter consisting of two layers separated by a vacuum is analyzed. The bottom layer consists of a selective emitting material such as a rare earth containing crystal on a metal substrate. The top layer, which blocks long wavelength radiation, is a window such as sapphire with a deposited metal film. As a result of reduced long wavelength emission, the theoretical analysis shows that the emitter efficiency can be increased by nearly a factor of 2.
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84.60.Jt Photoelectric conversion

Characterization and reduction of twist in Ge on insulator produced by localized liquid phase epitaxy

Douglas J. Tweet, Jong Jan Lee, Jer-Shen Maa, and Sheng Teng Hsu

Appl. Phys. Lett. 87, 141908 (2005); http://dx.doi.org/10.1063/1.2077860 (3 pages) | Cited 17 times

Online Publication Date: 28 September 2005

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Conditions for producing high-quality localized Ge-on-insulator film stacks on Si substrates by liquid phase epitaxy are discussed. In particular, we have found that the resulting Ge crystal planes have a tendency to exhibit a twist about the long axis of the crystal. If the wafer is heated much above the Ge melting temperature, this twist can be quite large ( ∼ 10°). The twist can be minimized by heating to just above the melting temperature and by using thicker Ge films. In spite of this twist, the Ge regions on top of the insulating Si3N4 are observed to be free of dislocations and stacking faults.
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61.72.Nn Stacking faults and other planar or extended defects
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Photoluminescence characteristics of coupled CdSe/ZnS quantum dots on self-assembled silica nanospheres

K. S. Kang, H. L. Ju, W. H. Han, J. H. Lee, J. G. Choi, and D. W. Boo

Appl. Phys. Lett. 87, 141909 (2005); http://dx.doi.org/10.1063/1.2081125 (3 pages) | Cited 2 times

Online Publication Date: 28 September 2005

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The photoluminescence (PL) characteristics of the self-assembled silica nanospheres containing coupled CdSe/ZnS core-shell quantum dots (QDs) on the surface of the sphere were studied. The degree of QD-coupling and the distribution of the coupled QDs were controlled by generating spatially separated QD-binding sites on the surface of the spheres and varying the QD concentration during the attachment process. When the sizes of QD spots on the surface probed by atomic force microscopy gradually increased, the band gap energy shifted to lower energy via strong Förster energy transfer between nearby QDs, and when UV-exposure time increased, the band gap energy shifted to slightly higher energy, accompanied by a large enhancement in the emission intensity. Moreover, the Bragg diffraction of the self-assembled crystal structure of the spheres affected the PL characteristics of QDs by shifting the entire emission spectra toward longer wavelength as the incident angles were increased.
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78.55.Et II-VI semiconductors
78.67.Hc Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
81.16.Dn Self-assembly
71.20.Nr Semiconductor compounds

Observation of the lamellar phase in a Zr-free Sm(Co0.45Fe0.15Cu0.4)5 alloy

Y. Zhang, A. M. Gabay, and G. C. Hadjipanayis

Appl. Phys. Lett. 87, 141910 (2005); http://dx.doi.org/10.1063/1.2081120 (3 pages) | Cited 1 time

Online Publication Date: 29 September 2005

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A lamellar phase is reported in a Zr-free Sm(Co0.45Fe0.15Cu0.4)5 alloy after it had been solutionized and aged at 650 °C for 50 h. The lamellar phase has a composition of Sm(Co,Fe,Cu)3 with a Be3Nb structure type, which is similar to that in the fully heat-treated Sm(Co,Cu,Fe,Zr)z 2:17 magnets containing Zr. This observation is contrary to the traditional thinking that associates the lamellar phase to the presence of Zr. This present result provides additional information that can be used to elaborate the origin of coercivity in precipitation Sm-Co magnets.
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75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
81.40.Gh Other heat and thermomechanical treatments
81.30.Mh Solid-phase precipitation

Strain relaxation in InAs/InGaAs quantum dots investigated by photoluminescence and capacitance-voltage profiling

J. F. Chen, R. S. Hsiao, Y. P. Chen, J. S. Wang, and J. Y. Chi

Appl. Phys. Lett. 87, 141911 (2005); http://dx.doi.org/10.1063/1.2081132 (3 pages) | Cited 13 times

Online Publication Date: 29 September 2005

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We present detailed studies of the onset of strain relaxation in InAs/InGaAs quantum dots. We show that the ground-state photoluminescence (PL) emission redshifts with increasing the InAs coverage before relaxation and blueshifts when relaxation occurs. PL spectra of the relaxed samples show two predominant families of dots with very different temperature-dependent efficiency. By comparison we show that the dots emitting at long wavelength are degraded by relaxation while the dots emitting at short wavelength remain coherently strained. Consequently, the PL spectra are dominated by the dots emitting at short wavelength, leading to the observed blueshift. This result suggests that the relaxation does not occur uniformly. In addition, we show that the relaxation occurs in the dot bottom interface.
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78.67.Hc Quantum dots
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.63.Kv Quantum dots

Fracture toughness of nanostructured silicon carbide

M. Ippolito, A. Mattoni, L. Colombo, and F. Cleri

Appl. Phys. Lett. 87, 141912 (2005); http://dx.doi.org/10.1063/1.2081135 (3 pages) | Cited 6 times

Online Publication Date: 29 September 2005

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By using atomistic simulations, we derive a constitutive equation for a microfractured β-SiC matrix containing hard or soft inclusions. The proposed equation is shown to follow the Eshelby theory for elastic inclusions, and appears to hold for any crack tip-inclusion distance and for a wide range of values of matrix-inclusion elastic mismatch. A comparison of the atomistic results with existing continuum elasticity models points out the weaknesses of some commonly adopted simplifying assumptions.
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81.05.Mh Cermets, ceramic and refractory composites
81.07.Bc Nanocrystalline materials
62.25.-g Mechanical properties of nanoscale systems
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.M- Structural failure of materials
62.20.D- Elasticity

High-quality GaNAs/GaAs quantum wells with light emission up to 1.44 μm grown by molecular-beam epitaxy

S. M. Wang, Q. F. Gu, Y. Q. Wei, M. Sadeghi, A. Larsson, Q. X. Zhao, X. D. Wang, C. H. Ma, and Z. G. Xing

Appl. Phys. Lett. 87, 141913 (2005); http://dx.doi.org/10.1063/1.2084337 (3 pages) | Cited 6 times

Online Publication Date: 29 September 2005

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High-quality GaNAs/GaAs quantum wells with high substitutional N concentrations, grown by molecular-beam epitaxy, are demonstrated using a reduced growth rate in a range of 0.125–1 μm/h. No phase separation is observed and the GaNAs well thickness is limited by the critical thickness. Strong room-temperature photoluminescence with a record long wavelength of 1.44 μm is obtained from an 18-nm-thick GaN0.06As0.94/GaAs quantum well.
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81.07.St Quantum wells
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Cr III-V semiconductors
78.67.De Quantum wells

Metal-adlayer-stabilized ZnO(0001) surfaces: Toward a new growth mode for oxides

J. E. Northrup and J. Neugebauer

Appl. Phys. Lett. 87, 141914 (2005); http://dx.doi.org/10.1063/1.2077862 (3 pages) | Cited 7 times

Online Publication Date: 30 September 2005

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First-principles total energy calculations were performed for clean and In-rich ZnO(0001) surfaces. The calculations indicate that Zn adlayers themselves are not energetically favorable, but that In can form a stable adlayer in Zn-rich conditions. This result opens the possibility that In may serve as a surfactant for the growth of ZnO.
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73.20.At Surface states, band structure, electron density of states
71.15.Nc Total energy and cohesive energy calculations

Dislocation-induced nonuniform interfacial reactions of Ti/Al/Mo/Au ohmic contacts on AlGaN/GaN heterostructure

Liang Wang, Fitih M. Mohammed, and Ilesanmi Adesida

Appl. Phys. Lett. 87, 141915 (2005); http://dx.doi.org/10.1063/1.2081136 (3 pages) | Cited 25 times

Online Publication Date: 30 September 2005

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Show Abstract
Transmission electron microscopy (TEM) is utilized to elucidate the postannealing interfacial microstructure of Ti/Al/Mo/Au metallization with AlGaN/GaN heterostructures to gain insight into the formation mechanism of low-resistance ohmic contacts. The reaction between the metal and the AlGaN layer does not proceed uniformly. Localized penetration through the AlGaN layer beyond the two-dimensional electron gas (2DEG) is observed while partial consumption of the AlGaN layer is noted in other areas. Analytical TEM analyses confirm that the main reaction product is TiN. A correlation between the appearance of TiN islands and threading dislocations is observed. Threading dislocations serve as short-circuit diffusion channels, and are responsible for the nonuniform reaction. TiN islands have a large total area of intimate contact with the 2DEG, and since no tunneling of electron through the AlGaN is required, a low-resistance ohmic contact is obtained.
Show PACS
68.35.Fx Diffusion; interface formation
68.35.Ct Interface structure and roughness
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)
73.40.Ns Metal-nonmetal contacts
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.72.Cc Kinetics of defect formation and annealing
85.40.Ls Metallization, contacts, interconnects; device isolation
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