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3 Jul 2006

Volume 89, Issue 1, Articles (01xxxx)

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Appl. Phys. Lett. 89, 011901 (2006); http://dx.doi.org/10.1063/1.2218670 (3 pages)

L. S. Wang, S. Tripathy, B. Z. Wang, J. H. Teng, S. Y. Chow, and S. J. Chua
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Nanoscale epitaxial overgrowth process and properties of GaN layers on Si (111) substrates

L. S. Wang, S. Tripathy, B. Z. Wang, J. H. Teng, S. Y. Chow, and S. J. Chua

Appl. Phys. Lett. 89, 011901 (2006); http://dx.doi.org/10.1063/1.2218670 (3 pages) | Cited 14 times

Online Publication Date: 5 July 2006

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Nanoscale epitaxial overgrowth has been explored to realize continuous specular GaN films on patterned SiO2/GaN/Si (111) substrates. We have employed both polystyrene-based nanosphere and interferometric lithographies to form the nanohole array patterns and then subsequent regrowth of GaN is carried out by metalorganic chemical vapor deposition. The nanoscale epitaxial overgrowth process of GaN layers is studied by scanning and transmission electron microscopy measurements. Optical spectroscopic methods such as microphotoluminescence and micro-Raman scattering show an improvement of the optical and crystalline quality in such overgrown GaN layers when compared to GaN simultaneously grown on bulk Si (111) without patterning. Realization of such thicker and good quality GaN layer would be useful to achieve III-nitride-based optoelectronic integration on Si substrates.
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68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.16.Nd Micro- and nanolithography
78.55.Cr III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Structure and photoluminescence properties of evaporated GeOx thin films

M. Ardyanian, H. Rinnert, X. Devaux, and M. Vergnat

Appl. Phys. Lett. 89, 011902 (2006); http://dx.doi.org/10.1063/1.2218830 (3 pages) | Cited 16 times

Online Publication Date: 5 July 2006

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Amorphous GeOx alloys were prepared by evaporation of GeO2 powder on substrates maintained at 100 °C. The evolution of the structure was investigated by infrared-absorption spectrometry, Raman spectrometry and transmission electron microscopy experiments for annealing temperatures less than 600 °C. These experiments allowed us to follow the phase separation of the alloy and to observe the appearance of amorphous and crystallized Ge aggregates. The evolution of the photoluminescence in the range of 560–1550 nm was correlated to the structure of the films.
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81.05.Cy Elemental semiconductors
81.05.Gc Amorphous semiconductors
68.55.-a Thin film structure and morphology
78.66.Db Elemental semiconductors and insulators
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.A- Nucleation and growth

Enhanced optical second harmonic generation in hybrid polymer nanoassemblies based on coupled surface plasmon resonance of a gold nanoparticle array

Miki Ishifuji, Masaya Mitsuishi, and Tokuji Miyashita

Appl. Phys. Lett. 89, 011903 (2006); http://dx.doi.org/10.1063/1.2219086 (3 pages) | Cited 11 times

Online Publication Date: 5 July 2006

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Effective utilization of coupled surface plasmon resonance from gold nanoparticles was demonstrated experimentally for optoelectronic applications based on second-order nonlinear optics. Hybrid polymer nanoassemblies were constructed by manipulating gold nanoparticle arrays with nonlinear optical active polymer nanosheets to investigate the second harmonic generation. The gold nanoparticle arrays were assembled on heterodeposited polymer nanosheets. The second harmonic light intensity was enhanced by a factor of 8. The observed enhancement was attributed to coupling of surface plasmons between two adjacent gold nanoparticles, thereby enhancing the surface electromagnetic field around the nanoparticles at the fundamental light wavelength (1064 nm).
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.68.+m Optical properties of surfaces
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Phase selective growth and properties of rhombohedral and cubic indium oxide

Ch. Y. Wang, V. Cimalla, H. Romanus, Th. Kups, G. Ecke, Th. Stauden, M. Ali, V. Lebedev, J. Pezoldt, and O. Ambacher

Appl. Phys. Lett. 89, 011904 (2006); http://dx.doi.org/10.1063/1.2219125 (3 pages) | Cited 28 times

Online Publication Date: 5 July 2006

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Phase selective growth of rhombohedral and cubic indium oxide polytypes was studied. The selective growth of different polytypes was achieved by adjusting substrate temperature and trimethylindium flow rate during metal organic chemical vapor deposition on c-plane sapphire. The optical band gaps of the cubic and rhombohedral phases were determined to be ∼ 3.7 and ∼ 3.0 eV, respectively. On the basis of the performed structural investigations, a phenomenological model of the nucleation and growth of highly textured cubic In2O3 on Al2O3 (0001) is proposed.
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68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.66.Li Other semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Propagation of surface water wave pulses over an uneven topographical bottom

Liang-Shan Chen, Sheng Li, Thomas F. George, Chao-Hsien Kuo, and Xin Sun

Appl. Phys. Lett. 89, 011905 (2006); http://dx.doi.org/10.1063/1.2219130 (3 pages) | Cited 1 time

Online Publication Date: 5 July 2006

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The propagation of surface water wave pulses over a topographical bottom with randomly arranged cylindrical steps is investigated by multiple scattering theory. It is shown that the waves within a certain frequency range can be localized due to the strong multiple scattering process. In the localized state, the wave intensity decreases exponentially as the transmitted distance increases. By making use of this effect, some components contained in the pulse can be filtered or inhibited by the cylinder ensemble and trapped for a relatively long period of time until dissipation.
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47.35.-i Hydrodynamic waves

Carrier capture times of the localized states in an InGaN thin film with indium-rich nanocluster structures

Hsiang-Chen Wang, Yen-Cheng Lu, Cheng-Yen Chen, and C. C. Yang

Appl. Phys. Lett. 89, 011906 (2006); http://dx.doi.org/10.1063/1.2219131 (3 pages) | Cited 5 times

Online Publication Date: 5 July 2006

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A femtosecond nondegenerate pump-probe technique of using two beta barium borate crystals for frequency doubling a 7 fs Ti:sapphire laser is used for studying the ultrafast carrier dynamics in an InGaN thin film, in which nanoscale indium-rich clusters have been observed. The carrier capture time of the localized states (the cluster states) from the free-carrier states (the states of the background compound) is calibrated. The initial rise times of the differential transmission of the probe intensity are calibrated to give the time constant of about 300 fs for the degenerate cases over the whole photoluminescence spectral range and for the nondegenerate cases, in which both pump and probe wavelengths correspond to the free-carrier states. However, when the carriers are excited in the free-carrier states and probed in the localized states, the rise time increases to the range of 590–715 fs, which represents the carrier capture time of the localized states from the free-carrier states.
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73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
78.47.-p Spectroscopy of solid state dynamics

Impurity-induced phase stabilization of semiconductors

Gustavo M. Dalpian, Yanfa Yan, and Su-Huai Wei

Appl. Phys. Lett. 89, 011907 (2006); http://dx.doi.org/10.1063/1.2218311 (3 pages) | Cited 6 times

Online Publication Date: 5 July 2006

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We propose an approach to stabilize the cubic zinc-blende (ZB) phase of semiconductor compounds that are usually more stable in the hexagonal wurtzite (WZ) phase. This approach is based on impurity doping and we take advantage of the band offset between the ZB and WZ phases. We show that introduction of donors should stabilize the one with lower conduction band (ZB), whereas holes should stabilize the one with higher valence band (WZ). A mechanism to invert the valence band offset is proposed in order to stabilize the ZB phase through holes. We used GaN, ZnO, and AlN as examples.
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71.20.Nr Semiconductor compounds
61.72.uj III-V and II-VI semiconductors
61.72.S- Impurities in crystals
71.55.Eq III-V semiconductors
71.55.Gs II-VI semiconductors

Two-dimensional nonclose-packed colloidal crystals formed by spincoating

Peng Jiang, Tushar Prasad, Michael J. McFarland, and Vicki L. Colvin

Appl. Phys. Lett. 89, 011908 (2006); http://dx.doi.org/10.1063/1.2218832 (3 pages) | Cited 45 times

Online Publication Date: 6 July 2006

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We report a simple spin-coating technique for the production of monolayer nonclose-packed colloidal crystals. Dispersions of submicron silica spheres in triacrylate monomers are spincoated and polymerized to form two-dimensional colloidal crystal-polymer nanocomposites. By removing the polymer matrix, wafer-scale nonclose-packed colloidal crystals with high crystalline quality can be made. The technique is compatible with standard microfabrication and allows for the production of microstructures for potential devices. Normal-incidence reflectivity spectra in the visible and near-infrared regions show sharp peaks due to Bragg diffraction from the colloidal monolayers. The peak position matches with the theoretical prediction using scalar wave approximation.
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81.16.-c Methods of micro- and nanofabrication and processing
82.35.-x Polymers: properties; reactions; polymerization
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
82.70.Dd Colloids
78.20.-e Optical properties of bulk materials and thin films

Unusual hydrogen distribution and its change in hydrogenated amorphous silicon prepared using bias electric-field molecular beam deposition

Nobuyuki Matsuki, Satoshi Shimizu, Michio Kondo, and Akihisa Matsuda

Appl. Phys. Lett. 89, 011909 (2006); http://dx.doi.org/10.1063/1.2219119 (3 pages)

Online Publication Date: 6 July 2006

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Hydrogenated amorphous silicon (a-Si:H) films prepared using a molecular beam deposition (MBD) method show an unusually sharp, narrow infrared absorption peak at 2080–2090 cm−1, which is thought to result from surface SiH species in the a-Si:H. The sharp, narrow peak is eliminated by a bias electric field of several kilovolts during deposition. The absence or presence of incoming high-energy silicon atoms or clusters accelerated by the field seems to be crucial for the resulting network structure and hydrogen distribution in a-Si:H prepared using MBD.
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78.66.Jg Amorphous semiconductors; glasses
78.66.Db Elemental semiconductors and insulators
78.30.Am Elemental semiconductors and insulators
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Method for analyzing the in-plane uniaxial anisotropy of soft magnetic thin film

Desheng Xue, Xiaolong Fan, and Changjun Jiang

Appl. Phys. Lett. 89, 011910 (2006); http://dx.doi.org/10.1063/1.2219127 (3 pages) | Cited 10 times

Online Publication Date: 6 July 2006

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Based on the vibrating sample magnetometer, a method is proposed to comprehensively analyze the in-plane uniaxial anisotropy of magnetic thin film. It can be used to determine accurately the values of effective anisotropy magnetic field Ha, anisotropy constants K1 and K2, as well as the directions of easy and hard axes. All of them can be carried out by fitting experimental M/Ms-θ0 curves with theoretical equations that only require one measurement. Using this method an effective anisotropy magnetic field Ha = 25.3 Oe and anisotropy constants K1 = 2.24×104 erg/cm3 and K2 = −4.7×103 erg/cm3 for the Co92Zr8 thin film were derived.
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75.70.Ak Magnetic properties of monolayers and thin films
07.55.Ge Magnetometers for magnetic field measurements
07.55.Jg Magnetometers for susceptibility, magnetic moment, and magnetization measurements
75.50.Cc Other ferromagnetic metals and alloys
75.30.Gw Magnetic anisotropy

Influence of V/III molar ratio on the formation of In vacancies in InN grown by metal-organic vapor-phase epitaxy

A. Pelli, K. Saarinen, F. Tuomisto, S. Ruffenach, and O. Briot

Appl. Phys. Lett. 89, 011911 (2006); http://dx.doi.org/10.1063/1.2219335 (3 pages) | Cited 20 times

Online Publication Date: 6 July 2006

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We have applied a slow positron beam to study InN samples grown by metal-organic vapor-phase epitaxy with different V/III molar ratios (3300–24 000) and at different growth temperatures (550–625 °C). Indium vacancies were identified in samples grown at V/III ratios below 4000. Their concentration is in the 1017cm−3 range. No strong dependence of vacancy concentration on the molar ratio was observed. At low V/III ratios, however, In droplets and vacancy clusters are formed near the substrate interface. The elevated growth temperature enhances the In vacancy formation, possibly due to limited sticking of In on the growth surface close to the decomposition temperature.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.A- Nucleation and growth
61.72.J- Point defects and defect clusters
81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Growth of Mg–Al spinel microcrystals on a sapphire surface using a solution-precipitation method

Che-Ming Liu and Jyh-Chen Chen

Appl. Phys. Lett. 89, 011912 (2006); http://dx.doi.org/10.1063/1.2220062 (3 pages)

Online Publication Date: 7 July 2006

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A solution-precipitation process was used to grow Mg–Al spinel microcrystals at etched pits in a c-axial sapphire single crystal surface. In the proposed innovative growth process, the etched pits function as heterogeneous nucleation points. The quenching and aging treatment causes Mg ions to diffuse into the sapphire crystal, precipitating as microcrystals at the etched pits. We found the precipitated crystals to be (111) Mg–Al spinels with a triangular pyramidal shape.
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81.10.Dn Growth from solutions
64.75.-g Phase equilibria
81.30.Mh Solid-phase precipitation
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.66.Fn Inorganic compounds

Thermal stress evolution in embedded Cu/low-k dielectric composite features

Conal E. Murray, Charles C. Goldsmith, Thomas M. Shaw, James P. Doyle, and I. C. Noyan

Appl. Phys. Lett. 89, 011913 (2006); http://dx.doi.org/10.1063/1.2219727 (3 pages) | Cited 5 times

Online Publication Date: 7 July 2006

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To determine the effect of low-modulus materials on the thermal stress evolution within interconnect metallization, thermal and residual stresses in copper features, embedded in an organosilicate glass (SiCOH) on a silicon substrate, were measured by x-ray diffraction as a function of temperature and calculated using finite element modeling. The elastic response of the structures was dictated by the thermal expansion mismatch between copper and silicon, the copper and SiCOH elastic moduli, and the composite geometry. The presence of a low-modulus layer between the features and underlying substrate plays a major role in the elastic stress relaxation generated during thermal cycling.
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81.05.Mh Cermets, ceramic and refractory composites
85.40.Ls Metallization, contacts, interconnects; device isolation
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
68.60.Bs Mechanical and acoustical properties
65.40.De Thermal expansion; thermomechanical effects

Insights into the origin of threading dislocations in GaN/Al2O3 from atomic force microscopy

Rachel A. Oliver, Menno J. Kappers, and Colin J. Humphreys

Appl. Phys. Lett. 89, 011914 (2006); http://dx.doi.org/10.1063/1.2219747 (3 pages) | Cited 14 times

Online Publication Date: 7 July 2006

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Threading dislocations in GaN/Al2O3 are widely assumed to arise at the coalescence boundaries of misoriented islands. We have used atomic force microscopy to study a large number of coalescence boundaries and found no significant difference between the threading dislocation density in the boundary regions and the overall threading dislocation density for the large islands observed on partially coalesced samples. A secondary population of smaller islands is observed with a significantly higher dislocation density, and we suggest that when these small islands are overgrown by large islands, these threading dislocations are incorporated into the large islands, resulting in dislocation clusters.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.37.Ps Atomic force microscopy (AFM)
68.35.B- Structure of clean surfaces (and surface reconstruction)
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