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30 Dec 2002

Volume 81, Issue 27, pp. 5099-5257

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Control of the morphology transition for the growth of cubic GaN/AlN nanostructures

E. Martinez-Guerrero, F. Chabuel, B. Daudin, J. L. Rouvière, and H. Mariette

Appl. Phys. Lett. 81, 5117 (2002); http://dx.doi.org/10.1063/1.1527975 (3 pages) | Cited 12 times

Online Publication Date: 19 December 2002

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The Stransky–Krastanow growth mode of strained layers which gives rise to a morphology transition from two-dimensional layer to three-dimensional islands is studied in details for the cubic gallium nitride on cubic aluminum nitride (GaN/AlN) system grown by molecular beam epitaxy. Besides the lattice parameter mismatch which governs this transition, we evidence the importance of two other parameters, namely the substrate temperature and the III/V flux ratio. Tuning each of these two parameters enables to control the strain relaxation mechanism of a GaN deposited onto AlN, leading to the growth of either quantum wells or quantum dots. © 2002 American Institute of Physics.
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81.07.St Quantum wells
81.07.Ta Quantum dots
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Determination of absolute indium content in InGaN/GaN multiple quantum wells using anomalous x-ray scattering

H. H. Lee, M. S. Yi, H. W. Jang, Y.-T. Moon, S.-J. Park, D. Y. Noh, M. Tang, and K. S. Liang

Appl. Phys. Lett. 81, 5120 (2002); http://dx.doi.org/10.1063/1.1530376 (3 pages) | Cited 9 times

Online Publication Date: 19 December 2002

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We have determined the absolute indium content incorporated in the crystalline lattice of InGaN films and InGaN/GaN multiple quantum wells using anomalous x-ray scattering (AXS). AXS spectra were obtained near the In K absorption edge at the InGaN (0006) Bragg peak where the InGaN Bragg reflection is well-resolved from the GaN reflections. By comparing the indium composition obtained by AXS to regular x-ray scattering results, which are also sensitive to the lattice strain, we determine the Poisson ratio of InGaN to be ν ≈ 0.23. The AXS method can be effective in determining absolute chemical composition of InGaN independent of the lattice strain, which is especially valuable for InGaN multiple quantum wells. © 2002 American Institute of Physics.
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68.65.Fg Quantum wells
78.70.Ck X-ray scattering

Morphological and mechanical properties of carbon-nanotube-reinforced semicrystalline and amorphous polymer composites

M. Cadek, J. N. Coleman, V. Barron, K. Hedicke, and W. J. Blau

Appl. Phys. Lett. 81, 5123 (2002); http://dx.doi.org/10.1063/1.1533118 (3 pages) | Cited 203 times

Online Publication Date: 19 December 2002

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In this work, multiwalled carbon nanotubes were investigated as potential mechanical reinforcement agents in two hosts, polyvinyl alcohol (PVA) and poly(9-vinyl carbazole) (PVK). It was found that, by adding various concentrations of nanotubes, both Young’s modulus and hardness increased by factors of 1.8 and 1.6 at 1 wt % in PVA and 2.8 and 2.0 at 8 wt % in PVK, in reasonable agreement with the Halpin–Tsai theory. Furthermore, the presence of the nanotubes was found to nucleate crystallization of the PVA. This crystal growth is thought to enhance matrix-nanotube stress transfer. In addition, microscopy studies suggest extremely strong interfacial bonding in the PVA-based composite. This is manifested by the fracture of the polymer rather that the polymer-nanotube interface. © 2002 American Institute of Physics.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.25.-g Mechanical properties of nanoscale systems
62.20.D- Elasticity
62.20.Qp Friction, tribology, and hardness
62.20.M- Structural failure of materials

Thermal conductivity of germanium, silicon, and carbon nitrides

D. T. Morelli and J. P. Heremans

Appl. Phys. Lett. 81, 5126 (2002); http://dx.doi.org/10.1063/1.1533840 (3 pages) | Cited 16 times

Online Publication Date: 19 December 2002

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We present a model calculation of the thermal conductivity of germanium nitride, silicon nitride, and carbon nitride in a temperature range in which intrinsic phonon scattering is dominant. We show that, in spite of the rather complex crystal structure of these nitrides, thermal conductivities exceeding 100 W m−1 K−1 can be attained in some of these compounds due to the combination of high Debye temperature and small Grüneisen constant. © 2002 American Institute of Physics.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions
63.20.-e Phonons in crystal lattices

Photoluminescence studies on InGaN/GaN multiple quantum wells with different degree of localization

M. Hao, J. Zhang, X. H. Zhang, and S. Chua

Appl. Phys. Lett. 81, 5129 (2002); http://dx.doi.org/10.1063/1.1531837 (3 pages) | Cited 13 times

Online Publication Date: 19 December 2002

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It has been found, by using photoluminescence (PL) studies, that both the localized states and nonradiative recombination centers in In0.06Ga0.94N/GaN multiple quantum wells (MQWs) can be greatly suppressed by inserting a monolayer of AlN before the growth of each well layer. While inserting a monolayer of AlN before each well layer does not have any effect on the growth rate or on the indium content of MQWs, it does improve room-temperature PL intensity of the In0.06Ga0.94N/GaN MQWs. The physics behind the suppression of localized states and nonradiative recombination centers is discussed. © 2002 American Institute of Physics.
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78.67.De Quantum wells
73.21.Fg Quantum wells
68.65.Fg Quantum wells
78.55.Cr III-V semiconductors
68.37.Lp Transmission electron microscopy (TEM)

Observation of orthogonally polarized transverse electric and transverse magnetic oscillation modes in a microcavity excited by localized two-photon absorption

Dru Morrish, Xiaosong Gan, and Min Gu

Appl. Phys. Lett. 81, 5132 (2002); http://dx.doi.org/10.1063/1.1531222 (3 pages) | Cited 6 times

Online Publication Date: 19 December 2002

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We report on the observation of orthogonally polarized transverse electric (TE) and transverse magnetic (TM) oscillation modes in a microcavity excited by localized two-photon absorption. The polarization-dependent features of morphology-dependent resonance (MDR) effects in a microsphere under two-photon fluorescence excitation are quantitatively investigated. In addition to a clear separation of excitation and resonance wavelengths under two-photon excitation, the fluorescence emission can be tightly controlled in three-dimensional space within a microsphere. The experimental results demonstrate not only the orthogonal polarization nature of TE and TM oscillation modes but also the dependence of the strength and the polarization properties of MDR peaks on excitation locations in a microsphere. © 2002 American Institute of Physics.
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42.25.Ja Polarization

Breakdown of the approximations of small perturbations in continuum modeling of amorphous thin film growth

C. Streng, K. Samwer, and S. G. Mayr

Appl. Phys. Lett. 81, 5135 (2002); http://dx.doi.org/10.1063/1.1532551 (3 pages) | Cited 4 times

Online Publication Date: 19 December 2002

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Morphology evolution of thin film growth can be quantitatively modeled by employing rate equations for two-dimensional, single-valued functions within a treatment of small perturbations. This description can be expected to be valid in an intermediate film thickness regime, where substrate influences and three-dimensional effects are minor. The breakdown of the mathematical description in its upper film thickness limit is systematically investigated by a detailed comparison of experiments and simulation. Possible reasons for the failure are discussed and improvements are suggested. © 2002 American Institute of Physics.
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68.55.A- Nucleation and growth
61.43.-j Disordered solids
68.35.B- Structure of clean surfaces (and surface reconstruction)

F-enhanced morphological and thermal stability of NiSi films on BF2+-implanted Si(001)

A. S. W. Wong, D. Z. Chi, M. Loomans, D. Ma, M. Y. Lai, W. C. Tjiu, S. J. Chua, C. W. Lim, and J. E. Greene

Appl. Phys. Lett. 81, 5138 (2002); http://dx.doi.org/10.1063/1.1533856 (3 pages) | Cited 20 times

Online Publication Date: 19 December 2002

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The morphological and thermal stability of conducting NiSi films formed on Si(001) are significantly enhanced by pre-implantation of the Si wafer with BF2+. In the absence of F, the maximum silicidation temperature Tmax is 650 °C; higher temperatures lead to the formation of the competing high-resistivity NiSi2 phase. Tmax, however, is increased to ⩾750 °C during NiSi formation on Si(001) implanted with 20 keV BF2+ at a dose of 5×1015 cm−2. The observed enhancement in NiSi thermal stability is due to F segregation to the silicide/Si(001) interface and silicide grain boundaries, which retards NiSi grain growth, leading to much smoother layers, and inhibits NiSi2 nucleation. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.60.Dv Thermal stability; thermal effects
68.35.Dv Composition, segregation; defects and impurities
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.72.Mm Grain and twin boundaries
61.72.Cc Kinetics of defect formation and annealing

Effects of 6H-SiC surface reconstruction on lattice relaxation of AlN buffer layers in molecular-beam epitaxial growth of GaN

Jun Suda, Kouhei Miura, Misako Honaga, Yusuke Nishi, Norio Onojima, and Hiroyuki Matsunami

Appl. Phys. Lett. 81, 5141 (2002); http://dx.doi.org/10.1063/1.1533855 (3 pages) | Cited 2 times

Online Publication Date: 19 December 2002

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Growth of GaN on on-axis 6H-SiC (0001)Si substrates with an AlN buffer layer was performed by molecular-beam epitaxy. The effects of SiC surface reconstruction on the lattice relaxation of AlN buffer layers and the crystalline quality of GaN layers were studied. High-temperature HCl-gas etching followed by HF chemical treatment resulted in an atomically flat SiC surface with a 1×1 structure. The AlN layer grown on the surface showed slow lattice relaxation. GaN grown on the AlN buffer layer exhibited the narrowest (0002) x-ray rocking curve of 70 arcsec and 107 cm−2 screw-type dislocation density, which was two orders of magnitude smaller than that of GaN grown on as-received substrates. © 2002 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.72.Lk Linear defects: dislocations, disclinations

Photoluminescence of Ge nanoparticles embedded in SiO2 glasses fabricated by a sol–gel method

Heqing Yang, Xingjun Wang, Huazhong Shi, Songhai Xie, Fujian Wang, Xiaoxiao Gu, and Xi Yao

Appl. Phys. Lett. 81, 5144 (2002); http://dx.doi.org/10.1063/1.1506943 (3 pages) | Cited 16 times

Online Publication Date: 19 December 2002

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Ge nanoparticles with different sizes in silica glasses were prepared by a sol–gel method using Cl3–Ge–C2H4–COOH as a Ge source. The size of the Ge nanoparticles decreases with a reduction in the content of Ge in the starting materials, and thus the optical absorption edge shifts to a higher energy. Silica gel glasses doped with Ge nanoparticles showed a strong room-temperature photoluminescence with peaks at 568, 607, 672, 722, and 775 nm. The peak position of photoluminescence spectrum scarcely depends on the Ge/Si ratio. However, the photoluminescence intensity increases sharply as the Ge/Si ratio is reduced. The photoluminescence arises from the Ge clusters of diameter of <1–2 nm with a molecular character instead of nanocrystalline Ge with the diamond structure. © 2002 American Institute of Physics.
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78.55.Ap Elemental semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.67.Hc Quantum dots
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.46.-w Structure of nanoscale materials

Fabrication of single- or double-row aligned self-assembled quantum dots by utilizing SiO2-patterned vicinal (001) GaAs substrates

Hyo Jin Kim, Junichi Motohisa, and Takashi Fukui

Appl. Phys. Lett. 81, 5147 (2002); http://dx.doi.org/10.1063/1.1534385 (3 pages) | Cited 2 times

Online Publication Date: 19 December 2002

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We investigated the formation of In0.8Ga0.2As self-assembled quantum dots (SAQDs) grown on SiO2-patterned 1°, 2°, and 5°-off (001) GaAs substrates by selective area metalorganic vapor phase epitaxy technique. The SiO2 patterns were filled with various stripe opening windows along the misorientation direction of the substrates. During the growth of the GaAs buffer layer on the opening regions, the steps on the (001) top facet was affected by the widths of the (001) top facet and the misorientation angles of the substrates. Single- or double-row aligned In0.8Ga0.2As SAQDs having definite interval were successfully fabricated on the (001) top facet with optimized top width and periodicity of step bunching. These results indicate that the selective growth technique of SAQDs by utilizing SiO2-patterned vicinal substrates is promising for nanoelectronic device applications such as single-electron memory devices. © 2002 American Institute of Physics.
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81.07.Ta Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.16.Dn Self-assembly
85.35.-p Nanoelectronic devices

Reversed truncated cone composition distribution of In0.8Ga0.2As quantum dots overgrown by an In0.1Ga0.9As layer in a GaAs matrix

A. Lenz, R. Timm, H. Eisele, Ch. Hennig, S. K. Becker, R. L. Sellin, U. W. Pohl, D. Bimberg, and M. Dähne

Appl. Phys. Lett. 81, 5150 (2002); http://dx.doi.org/10.1063/1.1533109 (3 pages) | Cited 39 times

Online Publication Date: 19 December 2002

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We present cross-sectional scanning tunneling microscopy results of self-organized In0.8Ga0.2As quantum dots covered by an In0.1Ga0.9As film inside a GaAs matrix prepared by metalorganic chemical vapor deposition. From images of quantum dots with atomic resolution, we determine a spatial distribution of the In composition within the dots with a shape of a reversed truncated cone. The wetting layer and the overgrown In0.1Ga0.9As layer show vertical intermixing. © 2002 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.08.Bc Wetting
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation

Correlation of resistivity with zinc content in a vapor grown (Cd,Zn)Te:Se

V. Corregidor, E. Diéguez, J. L. Castaño, M. Fiederle, V. Babentsov, A. Fauler, and K. Benz

Appl. Phys. Lett. 81, 5153 (2002); http://dx.doi.org/10.1063/1.1533124 (3 pages) | Cited 4 times

Online Publication Date: 19 December 2002

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We report the possibility to grow semi-insulating (Cd,Zn)Te:Se crystals by the modified Markov method (MMM) from the vapor phase. When oriented Cd(Te,Se) seed material was used for the growth, lattice matching and doping with Se resulted in an increase of resistivity up to several units of 109 Ω cm. A homogenous Zn distribution was also observed. The content of Se and Zn in the seed and grown crystals was determined by photoluminescence and energy dispersive analysis by x ray measurements. Resistivity and Zn concentration maps show a good spatial correlation in which the highest values of resistivity correspond to the areas of the highest Zn concentration. The main part of the crystals demonstrate a low extinction coefficient in the IR spectral region, except for the Zn inhomogeneity region. © 2002 American Institute of Physics.
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81.05.Dz II-VI semiconductors
81.10.Bk Growth from vapor
72.80.Ey III-V and II-VI semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
78.55.Et II-VI semiconductors
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Fs III-V and II-VI semiconductors

Dielectric functions and critical points of BexZn1−xTe alloys measured by spectroscopic ellipsometry

M. R. Buckley, F. C. Peiris, O. Maksimov, M. Muñoz, and M. C. Tamargo

Appl. Phys. Lett. 81, 5156 (2002); http://dx.doi.org/10.1063/1.1534387 (3 pages) | Cited 19 times

Online Publication Date: 19 December 2002

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Using a rotating analyzer spectroscopic ellipsometer, we have investigated the complex dielectric function of a series of ternary BexZn1−xTe thin films in the energy range between 0.7 and 6.5 eV for alloy concentrations between x = 0.0 and x = 0.52. After determining the alloy concentrations using x-ray diffraction and photoluminescence techniques, a standard inversion technique was used to obtain the optical constants from the measured ellipsometric spectra. Analyzing the second derivative of both the real and the imaginary parts of the dielectric constant, we have deduced the critical point parameters corresponding to the electronic transitions in the Brillouin zone. We find that the energy of the critical points with respect to Be concentration does not show any bowing effects unlike many other II–VI semiconductor ternary alloys. © 2002 American Institute of Physics.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Hf II-VI semiconductors
71.20.Nr Semiconductor compounds
77.22.Ch Permittivity (dielectric function)
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
07.60.Fs Polarimeters and ellipsometers
78.40.Fy Semiconductors
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