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13 Jun 2005

Volume 86, Issue 24, Articles (24xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 86, 241913 (2005); http://dx.doi.org/10.1063/1.1946181 (3 pages)

E. Placidi, F. Arciprete, V. Sessi, M. Fanfoni, F. Patella, and A. Balzarotti
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Interface atomic structure of epitaxial ErAs layers on (001) In0.53Ga0.47As and GaAs

Dmitri O. Klenov, Joshua M. Zide, Jeramy D. Zimmerman, Arthur C. Gossard, and Susanne Stemmer

Appl. Phys. Lett. 86, 241901 (2005); http://dx.doi.org/10.1063/1.1947910 (3 pages) | Cited 20 times

Online Publication Date: 6 June 2005

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High-angle annular dark-field (HAADF) imaging in scanning transmission electron microscopy was used to determine the atomic structure of interfaces between epitaxial ErAs layers with the cubic rock salt structure and In0.53Ga0.47As and GaAs, respectively. All layers were grown by molecular-beam epitaxy. We show that the interfacial atomic arrangement corresponds to the so-called chain model, in which the zinc blende semiconductor is terminated with a Ga layer. Image analysis was used to quantify the expansion between the first ErAs plane and the terminating Ga plane. In the HAADF images, a high intensity transfer from the heavy Er columns into the background was observed in the ErAs layer, whereas the background in In0.53Ga0.47As was of much lower intensity.
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68.35.Ct Interface structure and roughness
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.37.Lp Transmission electron microscopy (TEM)
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Electromigration-induced grain rotation in anisotropic conducting beta tin

Albert T. Wu, A. M. Gusak, K. N. Tu, and C. R. Kao

Appl. Phys. Lett. 86, 241902 (2005); http://dx.doi.org/10.1063/1.1941456 (3 pages) | Cited 15 times

Online Publication Date: 6 June 2005

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Electromigration in beta-Sn has shown a 10% drop of resistance due to the anisotropic properties of the material. The drop was proposed due to reorientation of grains to reduce the resistance. The driving force as well as the atomic mechanism of grain rotation under electromigration has been considered in this letter. We propose that the anisotropic resistivity causes the divergence of the vacancy fluxes at the grain boundaries and induces the vacancy fluxes to/from the free surface along the grain boundary. The vacancy gradients along the grain boundaries correspond to the gradients of stress. The opposite sign of the stress along grain boundaries generates a torque which leads to rotation of the grain by grain boundary diffusion or creep. The rate of rotation estimated on the base of the model seems to agree well with the observed experimental data.
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81.05.Bx Metals, semimetals, and alloys
66.30.Qa Electromigration
61.72.Mm Grain and twin boundaries
66.30.Lw Diffusion of other defects
61.72.J- Point defects and defect clusters

Enhanced annihilations of self-interstitial clusters by vacancies transported through vehicle action of Cu in Cu-implanted silicon crystals

Minoru Nakamura and Susumu Murakami

Appl. Phys. Lett. 86, 241903 (2005); http://dx.doi.org/10.1063/1.1947383 (3 pages)

Online Publication Date: 7 June 2005

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Thermal behaviors of intrinsic defect clusters (self-interstitials and vacancies) in silicon crystals implanted with several metals including Cu were observed by photoluminescence measurements to investigate the influences of the metals on the diffusion of the intrinsic defects. Enhanced annihilations (EAs) of the defect clusters were observed only for an oxygen-lean floating zone (FZ) crystal implanted with Cu and annealed at temperatures between 400 °C and 600 °C, while they were not observed for any types of crystals (n- and p-type FZ and Czochralski crystals) implanted with Fe and Cr. The EAs of the defect clusters were well explained by a vehicle action of fast diffusing Cu for vacancy transportation.
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61.72.J- Point defects and defect clusters
71.55.Cn Elemental semiconductors
61.72.uf Ge and Si
78.55.Ap Elemental semiconductors
61.72.Cc Kinetics of defect formation and annealing
66.30.Lw Diffusion of other defects

Effect of threading dislocations on the Bragg peakwidths of GaN, AlGaN, and AlN heterolayers

S. R. Lee, A. M. West, A. A. Allerman, K. E. Waldrip, D. M. Follstaedt, P. P. Provencio, D. D. Koleske, and C. R. Abernathy

Appl. Phys. Lett. 86, 241904 (2005); http://dx.doi.org/10.1063/1.1947367 (3 pages) | Cited 55 times

Online Publication Date: 7 June 2005

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We develop a reciprocal-space model that describes the (hkl) dependence of the broadened Bragg peakwidths produced by x-ray diffraction from a dislocated epilayer. We compare the model to experiments and find that it accurately describes the peakwidths of 16 different Bragg reflections in the [010] zone of both GaN and AlN heterolayers. Using lattice-distortion parameters determined by fitting the model to selected reflections, we estimate threading-dislocation densities for seven different GaN and AlGaN samples and find improved agreement with transmission electron microscopy measurements.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.05.Ea III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.37.Lp Transmission electron microscopy (TEM)

Effects of electromigration-induced void dynamics on the evolution of electrical resistance in metallic interconnect lines

Jaeseol Cho, M. Rauf Gungor, and Dimitrios Maroudas

Appl. Phys. Lett. 86, 241905 (2005); http://dx.doi.org/10.1063/1.1947373 (3 pages) | Cited 15 times

Online Publication Date: 7 June 2005

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The effects of void dynamics under electromigration conditions on the electrical resistance evolution in metallic thin-film interconnects are examined based on self-consistent dynamical simulations. Changes in the interconnect line resistance are found to depend strongly on electromigration-induced void morphological changes and are explained on the basis of void extension across the linewidth and void surface area evolution at constant void volume. The void morphological evolution may lead to stable steady or time-periodic line resistance response or to abrupt resistance increase associated with failure. Our computational results imply that electrical resistance increases should not be attributed only to void formation or void growth and that electrical resistance oscillations are not due to alternating defect generation and annihilation. The results are in excellent agreement with analytical scaling theories and qualitatively consistent with a large set of experimental electrical resistance measurements.
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85.40.Ls Metallization, contacts, interconnects; device isolation
73.61.At Metal and metallic alloys
61.72.Qq Microscopic defects (voids, inclusions, etc.)
66.30.Qa Electromigration

Measure of disorder in tetrahedrally bonded semiconductors

S. Tripura Sundari and G. Raghavan

Appl. Phys. Lett. 86, 241906 (2005); http://dx.doi.org/10.1063/1.1947904 (3 pages) | Cited 1 time

Online Publication Date: 7 June 2005

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A measure of crystalline order in tetrahedrally bonded semiconductors is proposed based on optical response. This measure is obtained from the ⟨111⟩ critical point structure in the dielectric spectra. This descriptor is sensitive to the nature and extent of disorder in specimens and distinguishes differences in medium and short-order present in amorphous materials. Application to Ar+-irradiated Si specimens yields the threshold amorphization dose and this technique is sensitive to structural changes which occur as a function of irradiation fluence both above and beyond the amorphization threshhold. Systematic variations are also obtained in hydrogenated amorphous-Si. The general validity of the method is indicated.
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61.43.Dq Amorphous semiconductors, metals, and alloys
61.72.uf Ge and Si
61.80.Jh Ion radiation effects
61.50.Ks Crystallographic aspects of phase transformations; pressure effects
64.70.K- Solid-solid transitions

Effect of annealing temperature ramp rate on bubble formation in helium-implanted silicon

Todd W. Simpson and Ian V. Mitchell

Appl. Phys. Lett. 86, 241907 (2005); http://dx.doi.org/10.1063/1.1947384 (3 pages) | Cited 9 times

Online Publication Date: 8 June 2005

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We have implanted math into Si(100) at 1.0 MeV ion energy and to fluences ranging between 2×1015 and 2×1016 cm−2, followed by annealing at 700 °C. Heating ramp rates have been systematically varied over more than two decades (0.3 °C/s to 100 °C/s) at each fluence. The retention of math is measured through the math(d,p)math nuclear reaction yield. We show that gas retention can be varied by more than an order of magnitude even while the other anneal parameters—anneal temperature and anneal time—are maintained constant. Cross-sectional scanning electron micrographs confirm the presence of planetarylike cavity structures at a depth closely matching that calculated for the damage peak.
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81.05.Cy Elemental semiconductors
61.72.uf Ge and Si
61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.72.Cc Kinetics of defect formation and annealing
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
68.47.Fg Semiconductor surfaces

Experimental confirmation of negative phase change in negative index material planar samples

D. Vier, D. R. Fredkin, A. Simic, S. Schultz, and Minas Tanielian

Appl. Phys. Lett. 86, 241908 (2005); http://dx.doi.org/10.1063/1.1947903 (3 pages) | Cited 3 times

Online Publication Date: 8 June 2005

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We use far-field range measurements to determine and confirm the negative phase change through a planar negative index material as a function of frequency. The metamaterial is composed of wires and split ring resonators. At frequencies for which the surface impedance Z/Z0 = 1, we determine the index (n) from the measured phase change (relative to a vacuum) and via numerical simulation. In addition to confirming the simulated negative phase change at the frequency where n = −1, we find good agreement with prior Snell’s law measurements from n = −2.5 to −0.5. This illustrates that measuring the phase change of the transmitted signal can be a practical means of identifying the existence of negative index in planar test samples.
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84.40.-x Radiowave and microwave (including millimeter wave) technology
84.40.Az Waveguides, transmission lines, striplines
41.20.Jb Electromagnetic wave propagation; radiowave propagation

Bulk metallic glass formation in Zr–Cu–Fe–Al alloys

Kaifeng Jin and Jörg F. Löffler

Appl. Phys. Lett. 86, 241909 (2005); http://dx.doi.org/10.1063/1.1948513 (3 pages) | Cited 31 times

Online Publication Date: 8 June 2005

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We have discovered a series of bulk metallic glass-forming alloys of composition (ZrxCu100−x)80(Fe40Al60)20 with x = 68–77 and have investigated them by x-ray diffraction, small-angle neutron scattering, and differential scanning calorimetry. All of these alloys exhibit a calorimetric glass transition temperature of 670 K<Tg<687 K and a large undercooled liquid region of widths 73–86 K. The best glass-forming ability is obtained for x ≈ 72.5, i.e., for the alloy Zr58Cu22Fe8Al12. In rod shape this alloy has a critical casting thickness of 13 mm, as verified by detailed casting experiments, while alloys with x = 68 and 77 can still be cast to a thickness of 5 mm. Furthermore, the region where glassy samples with a thickness of 0.5 mm can be prepared extends from x = 62–81. The best glass-former, Zr58Cu22Fe8Al12, has a tensile yield strength of 1.71 GPa and shows an elastic limit of 2.25%. This new class of Ni-free Zr-based alloys is potentially very interesting for biomedical applications.
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81.05.Kf Glasses (including metallic glasses)
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
61.43.Fs Glasses

Random conductivity of δ-Bi2O3 films

N. V. Skorodumova, A. K. Jonsson, M. Herranen, M. Strømme, G. A. Niklasson, B. Johansson, and S. I. Simak

Appl. Phys. Lett. 86, 241910 (2005); http://dx.doi.org/10.1063/1.1948516 (3 pages) | Cited 11 times

Online Publication Date: 8 June 2005

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The experimental investigation of the cubic δ-Bi2O3 phase grown on a (110) Au substrate at low temperature has disclosed a chaotic character of the conductivity at low voltage and temperature. Based on first-principles calculations, we show that the conductivity of this oxide strongly depends on the distribution of oxygen ions and that oxygen migration is able to cause a momentary switch of the conduction mechanism.
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73.61.-r Electrical properties of specific thin films

Indium redistribution in an InGaN quantum well induced by electron-beam irradiation in a transmission electron microscope

T. Li, E. Hahn, D. Gerthsen, A. Rosenauer, A. Strittmatter, L. Reißmann, and D. Bimberg

Appl. Phys. Lett. 86, 241911 (2005); http://dx.doi.org/10.1063/1.1948517 (3 pages) | Cited 21 times

Online Publication Date: 8 June 2005

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The change of the morphology and indium distribution in an In0.12Ga0.88N quantum well embedded in GaN was investigated depending on the duration of electron-beam irradiation in a transmission electron microscope. Strain-state analysis based on high-resolution lattice-fringe images was used to determine quantitatively the local and average indium concentration of the InGaN quantum well. In-rich clusters were found already in the first image taken after 20 s of irradiation. The indium concentration in the clusters tends to increase with prolonged irradiation time. In contrast, the locally averaged indium concentration and the quantum-well width do not change within the first minute.
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68.65.Fg Quantum wells
61.80.Fe Electron and positron radiation effects
61.82.Fk Semiconductors

Dynamics of the formation of polymeric microstructures induced by electrohydrodynamic instability

Ning Wu and William B. Russel

Appl. Phys. Lett. 86, 241912 (2005); http://dx.doi.org/10.1063/1.1949288 (3 pages) | Cited 16 times

Online Publication Date: 8 June 2005

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We perform two-dimensional simulations of an electrohydrodynamic patterning process for a mask-gap-polymer-substrate sandwich. The simulations help us identify the intrinsic pattern resulting from nonlinear interactions to be hexagonal when the mask is unpatterned, consistent with experimental observations. The dynamic evolution of the thin polymer layer under a patterned mask shows that the pillars start to form from corners, propagate along edges, and then grow inwards. This growth sequence, identical to experimental observations, creates a square pattern under a square mask, a hexagonal pattern under a triangular mask, etc. Besides the hexagonal pattern, simulations indicate the conditions under which various different patterns that have been observed in experiments should form.
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81.16.Rf Micro- and nanoscale pattern formation
85.40.Hp Lithography, masks and pattern transfer
61.41.+e Polymers, elastomers, and plastics
47.65.-d Magnetohydrodynamics and electrohydrodynamics

Step erosion during nucleation of InAs/GaAs(001) quantum dots

E. Placidi, F. Arciprete, V. Sessi, M. Fanfoni, F. Patella, and A. Balzarotti

Appl. Phys. Lett. 86, 241913 (2005); http://dx.doi.org/10.1063/1.1946181 (3 pages) | Cited 29 times

Online Publication Date: 9 June 2005

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We have investigated, by means of atomic force microscopy, the complete evolution of InAs/GaAs(001) quantum dots as a function of deposited InAs. Direct evidence is found for step erosion by quantum dots nucleated onto the step edge and an estimate of the eroded volume is provided. By studying the quantum dots volume as a function of InAs coverage, we show that the wetting layer contribution is confined within a narrow range of coverage around the two- and three-dimensional transition.
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81.07.Ta Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
68.37.Ps Atomic force microscopy (AFM)
64.60.Q- Nucleation

Rechargeable hydrogen storage in nanostructured mixtures of hydrogenated carbon and lithium hydride

Takayuki Ichikawa, Hironobu Fujii, Shigehito Isobe, and Koji Nabeta

Appl. Phys. Lett. 86, 241914 (2005); http://dx.doi.org/10.1063/1.1946188 (3 pages) | Cited 18 times

Online Publication Date: 9 June 2005

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A hydrogen storage ability caused by the interaction between nanostructured carbon (CnanoHx) and lithium hydride (LiH) is demonstrated, which should be recognized as Li-C-H system in the H-storage materials. Especially, the 2:1 mixture of CnanoHx and LiH exhibited promising hydrogen storage properties with a rechargeable hydrogen capacity of more than 4 mass% below 350 °C, preserving the nanostructural feature in the mixture even after hydrogen release. On the other hand, the 1:2 and 1:1 mixtures exhibited the crystal growth of Li2C2 after hydrogen desorption, leading to poorer hydrogen rechargeability.
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81.07.Bc Nanocrystalline materials
84.60.-h Direct energy conversion and storage
68.43.Mn Adsorption kinetics
61.46.-w Structure of nanoscale materials

Picosecond photoelectric characteristic in La0.7Sr0.3MnO3/Si p-n junctions

Hui-Bin Lu, Kui-Juan Jin, Yan-Hong Huang, Meng He, Kun Zhao, Bo-Lin Cheng, Zheng-Hao Chen, Yue-Liang Zhou, Sou-Yu Dai, and Guo-Zhen Yang

Appl. Phys. Lett. 86, 241915 (2005); http://dx.doi.org/10.1063/1.1946901 (3 pages) | Cited 56 times

Online Publication Date: 9 June 2005

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Ultrafast photoelectric effects have been observed in La0.7Sr0.3MnO3/Si p-n junctions fabricated by laser molecular-beam epitaxy. The rise time was ∼ 210 ps and the full width at half-maximum was ∼ 650 ps for the photovoltaic pulse when the junction was irradiated by a 1064 nm laser pulse of 25 ps duration. The photovoltaic sensitivity was as large as 435 mV/mJ for a 1064 nm laser pulse. No such photovoltaic signal was observed with irradiation from a 10.6 μm CO2 laser pulse. The results reveal that this phenomenon is an ultrafast photoelectric effect.
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72.40.+w Photoconduction and photovoltaic effects
78.47.-p Spectroscopy of solid state dynamics
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Pz Photoconduction and photovoltaic effects

Studies of silicon dihydride and its potential role in light-induced metastability in hydrogenated amorphous silicon

T. A. Abtew, D. A. Drabold, and P. C. Taylor

Appl. Phys. Lett. 86, 241916 (2005); http://dx.doi.org/10.1063/1.1943488 (3 pages) | Cited 5 times

Online Publication Date: 10 June 2005

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Recent nuclear magnetic resonance experiments on protons in hydrogenated amorphous silicon (a‐Si:H) by T. Su, P. C. Taylor, G. Ganguly, and D. E. Carlson [Phys. Rev. Lett. 89, 015502 (2002) ] have shown that light exposure leads to structures involving two protons separated by 2.3±0.2 Å. In this report, using supercell models of a‐Si:H, we show that SiH2 configurations in the solid state are consistent with these observations. We find an average proton distance of 2.39 Å for SiH2 structures considered for four different configurations. We also find that the details of basis set and density functional are important for accurately representing these structures.
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72.40.+w Photoconduction and photovoltaic effects
72.80.Ng Disordered solids
61.43.Dq Amorphous semiconductors, metals, and alloys

Activation volume and density of mobile dislocations in plastically deforming nanocrystalline Ni

Y. M. Wang, A. V. Hamza, and E. Ma

Appl. Phys. Lett. 86, 241917 (2005); http://dx.doi.org/10.1063/1.1946899 (3 pages) | Cited 39 times

Online Publication Date: 10 June 2005

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We report the analysis of repeated transients to monitor the coupled evolution of dislocation velocity and mobile dislocation density in plastically deforming nanocrystalline Ni. The stress relaxation series allowed the determination of the physical activation volume, indicating a rate-controlling mechanism different from that in coarse-grained Ni. The mobile dislocation exhaustion observed is correlated with the unusually high apparent work-hardening rate during the early stage of straining.
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81.05.Bx Metals, semimetals, and alloys
81.07.Bc Nanocrystalline materials
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
66.30.Lw Diffusion of other defects
61.46.-w Structure of nanoscale materials
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
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