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24 May 1999

Volume 74, Issue 21, pp. 3081-3230

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Stress analysis of selective epitaxial growth of GaN

Q. K. K. Liu, A. Hoffmann, H. Siegle, A. Kaschner, C. Thomsen, J. Christen, and F. Bertram

Appl. Phys. Lett. 74, 3122 (1999); http://dx.doi.org/10.1063/1.124082 (3 pages) | Cited 15 times

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Stress distributions in selectively overgrown self-organized GaN hexagonal pyramids have been analyzed by continuum elasticity theory. This has been carried out using the values for the moduli of elasticity found in the literature and an effective lattice mismatch between the GaN and the substrate that was determined from the Raman shift of the GaN buffer layer. The results of compressive stress in the buffer layer, tensile stress on the lower half of the pyramids’ facet surface, and full relaxation for approximately the upper 2/3 of the pyramids are in satisfactory agreement with the experimental observations that were deduced from cathodoluminescence microscopy and micro-Raman spectroscopy. © 1999 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
62.20.D- Elasticity
81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence

Temperature dependence of Raman scattering in single crystal GaN films

Ming S. Liu, Les A. Bursill, S. Prawer, K. W. Nugent, Y. Z. Tong, and G. Y. Zhang

Appl. Phys. Lett. 74, 3125 (1999); http://dx.doi.org/10.1063/1.124083 (3 pages) | Cited 47 times

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Micro-Raman scattering from single crystal GaN films, both free-standing and attached to Al2O3 substrates, was performed over the temperature range from 78 to 800 K. These measurements reveal that the Raman phonon frequency decreases and the linewidth broadens with increasing temperature. This temperature dependence is well described by an empirical relationship which has proved to be effective for other semiconductors. The experiments also demonstrate that the strain from Al2O3 substrates compresses the epitaxial GaN in the c-axis direction. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
68.55.-a Thin film structure and morphology
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Optical investigation of InGaN/GaN multiple quantum wells

T. Wang, D. Nakagawa, M. Lachab, T. Sugahara, and S. Sakai

Appl. Phys. Lett. 74, 3128 (1999); http://dx.doi.org/10.1063/1.124084 (3 pages) | Cited 31 times

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Optical investigation was performed on InGaN/GaN multiple quantum well (MQW) structures with different well thicknesses. At low temperature, the excitation power dependence of the photoluminescence (PL) emission energy of a MQW with 5 nm well thickness was found to be different from that of a MQW with 2.5 nm well thickness. Their temperature dependence of the optical behaviors including the PL line shapes and the internal quantum efficiencies also showed distinct features. The optical behaviors of the quantum well with a thickness above 2.5 nm can be explained by a model based on the formation of self-organized small In-rich regions, rather than by the piezoelectric field-induced quantum-confined Stark effect. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
64.75.-g Phase equilibria
78.20.Jq Electro-optical effects

Distributed on-fiber thin film heaters for Bragg gratings with adjustable chirp

John A. Rogers, Benjamin J. Eggleton, Janet R. Pedrazzani, and Thomas A. Strasser

Appl. Phys. Lett. 74, 3131 (1999); http://dx.doi.org/10.1063/1.124085 (3 pages) | Cited 26 times

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This letter describes a fiber Bragg grating device that has tunable chirp. It relies on a distributed on-fiber resistive heater that consists of a thin metal film deposited onto the outer surface of a bare fiber; the thickness of this film varies continuously with position along the fiber. The physics of heat flow and diffusion in these structures leads to temperature gradients that follow, to a remarkably good approximation, the local resistance of the tapered metal film. This temperature distribution produces a chirp with a geometry that is defined by the thickness profile of the film and at a rate that can be adjusted by changing the current. Finite element modeling illuminates aspects of the flow of heat in these structures, and optical measurements demonstrate important characteristics of the devices. © 1999 American Institute of Physics.
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42.81.Wg Other fiber-optical devices
42.79.Dj Gratings
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
07.20.Hy Furnaces; heaters

Optical nonlinearity in low-temperature-grown GaAs: Microscopic limitations and optimization strategies

M. Haiml, U. Siegner, F. Morier-Genoud, U. Keller, M. Luysberg, R. C. Lutz, P. Specht, and E. R. Weber

Appl. Phys. Lett. 74, 3134 (1999); http://dx.doi.org/10.1063/1.124086 (3 pages) | Cited 27 times

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We have quantitatively measured the linear and the nonsaturable absorption as well as the absorption modulation and its recovery time in as-grown and annealed low-temperature (LT) GaAs. Correlation of the optical data with As antisite (AsGa) defect densities yields the absorption cross section and the saturation parameter of the dominant AsGa to the conduction-band defect transition. We show that this defect transition is mainly responsible for the large nonsaturable absorption in as-grown LT GaAs with fast recovery times. Reducing the AsGa density by annealing yields an optimized material with small nonsaturable absorption, high absorption modulation, and fast recovery times. © 1999 American Institute of Physics.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing
71.55.Eq III-V semiconductors
71.20.Nr Semiconductor compounds
78.47.-p Spectroscopy of solid state dynamics

Concentration-controlled phase selection of silicide formation during reactive deposition

A. Vantomme, S. Degroote, J. Dekoster, G. Langouche, and R. Pretorius

Appl. Phys. Lett. 74, 3137 (1999); http://dx.doi.org/10.1063/1.124090 (3 pages) | Cited 35 times

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Slow (low-rate) reactive deposition of a metal onto a Si substrate can result in direct formation of a metal disilicide, thereby skipping the metal-rich phases in the formation sequence. These observations have been explained thermodynamically by using the effective heat of formation model. As a result of this concentration-controlled phase selection, it is possible to form disilicides, such as CoSi2, NiSi2, or β-FeSi2 at much lower growth temperatures than possible in conventional solid-phase reaction of a metal layer deposited onto Si at room temperature (i.e., lower than the nucleation temperature). Moreover, epitaxial growth of CoSi2/Si(100), which is not possible by solid-phase reaction, becomes achievable when depositing Co atoms sufficiently slowly onto a heated Si substrate. © 1999 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.40.Sz Deposition technology
81.15.Kk Vapor phase epitaxy; growth from vapor phase
85.40.Ls Metallization, contacts, interconnects; device isolation
82.60.Cx Enthalpies of combustion, reaction, and formation
81.15.Aa Theory and models of film growth

GHz bandwidth GaAs light-emitting diodes

C. H. Chen, M. Hargis, J. M. Woodall, M. R. Melloch, J. S. Reynolds, E. Yablonovitch, and W. Wang

Appl. Phys. Lett. 74, 3140 (1999); http://dx.doi.org/10.1063/1.124092 (3 pages) | Cited 13 times

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Double-heterostructure GaAs/GaAlAs light-emitting diodes (LEDs) have been fabricated with the emitter regions beryllium doped to 2×1019 and 7×1019 cm−3. The 7×1019 cm−3 doped emitters have an internal quantum efficiency of 10% and an optical modulation bandwidth of 1.7 GHz. The steady-state optical output power versus the input current shows an external efficiency of 2.5 μW/mA. The 2×1019 cm−3 emitters have internal quantum efficiencies as high as 80%, but a reduced cutoff frequency. The external quantum efficiency reaches 10 μW/mA. These high-speed LEDs are produced by reducing the radiative lifetime to 100–250 ps without significantly degrading internal quantum efficiency. The current results on heavily beryllium-doped LEDs exhibit, to the best of our knowledge, the highest external efficiencies to date for such high doping and efficiencies close to that observed for lower-doped LEDs. © 1999 American Institute of Physics.
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85.60.Jb Light-emitting devices
61.72.uj III-V and II-VI semiconductors
78.60.Fi Electroluminescence
78.66.Fd III-V semiconductors
42.79.Sz Optical communication systems, multiplexers, and demultiplexers

Effects of interfacial layer growth on the electrical characteristics of thin titanium oxide films on silicon

Byoung Hun Lee, Yongjoo Jeon, Keith Zawadzki, Wen-Jie Qi, and Jack Lee

Appl. Phys. Lett. 74, 3143 (1999); http://dx.doi.org/10.1063/1.124089 (3 pages) | Cited 50 times

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Effects of interfacial layer growth on reactively sputter-deposited TiO2 films were studied. Leakage current was reduced to 10−8 A/cm2 at +1 V after annealing in oxygen ambient and showed tunneling-like temperature dependence. As the interfacial layer grew, interface states and hysteresis were improved significantly. However, the reliability was degraded as the annealing temperature increased. © 1999 American Institute of Physics.
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73.61.Ng Insulators
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
77.55.-g Dielectric thin films
61.72.Cc Kinetics of defect formation and annealing
77.22.Jp Dielectric breakdown and space-charge effects
73.20.-r Electron states at surfaces and interfaces
84.32.Tt Capacitors

Photoluminescence from silicon nanoparticles in a diamond matrix

M. L. Terranova, S. Piccirillo, V. Sessa, S. Botti, and M. Rossi

Appl. Phys. Lett. 74, 3146 (1999); http://dx.doi.org/10.1063/1.124088 (3 pages) | Cited 5 times

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Composite polycrystalline diamond layers containing light-emitting Si nanoparticles (mean diameter: 3.6 and 6.2 nm) have been prepared by using a chemical-vapor deposition technique coupled with a powder-flowing apparatus. The room-temperature photoluminescence behavior of such material in the 1.6–2.5 eV energy range is found characterized by a strong increase of the emission efficiency from the Si nanostructures embedded in the diamond matrix. Moreover, the studies reveal that it is possible to tune the luminescence frequency in the yellow-green spectral region by selecting the size of the inserted Si grains. © 1999 American Institute of Physics.
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78.66.Vs Fine-particle systems
78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.05.Cy Elemental semiconductors

Electrical transport in pure and boron-doped carbon nanotubes

Bingqing Wei, Ralph Spolenak, Philipp Kohler-Redlich, Manfred Rühle, and Eduard Arzt

Appl. Phys. Lett. 74, 3149 (1999); http://dx.doi.org/10.1063/1.124093 (3 pages) | Cited 77 times

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The resistivities of individual multiwalled pure and boron-doped carbon nanotubes have been measured in the temperature range from 25 to 300 °C. The connection patterns were formed by depositing two-terminal tungsten wires on a nanotube using focused-ion-beam lithography. A decrease of the resistivity with increasing temperature, i.e., a semiconductor-like behavior, was found for both B-doped and pure carbon nanotubes. B-doped nanotubes have a reduced room-temperature resistivity (7.4×10−7–7.7×10−6 Ωm) as compared to pure nanotubes (5.3×10−6–1.9×10−5 Ωm), making the resistivity of the doped tubes comparable to those along the basal plane of graphite. The activation energy derived from the resistivity versus temperature Arrhenius plots was found to be smaller for the B-doped (55–70 meV) than for the pure multiwalled nanotubes (190–290 meV). © 1999 American Institute of Physics.
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72.20.Fr Low-field transport and mobility; piezoresistance
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
72.80.Rj Fullerenes and related materials

Tensile tests of ropes of very long aligned multiwall carbon nanotubes

Z. W. Pan, S. S. Xie, L. Lu, B. H. Chang, L. F. Sun, W. Y. Zhou, G. Wang, and D. L. Zhang

Appl. Phys. Lett. 74, 3152 (1999); http://dx.doi.org/10.1063/1.124094 (3 pages) | Cited 81 times

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We have directly measured the Young’s modulus and tensile strength of multiwall carbon nanotubes by pulling very long (∼2 mm) aligned nanotube ropes with a specially designed stress-strain puller. This puller can apply an axial force to the rope and simultaneously measure the corresponding rope elongation and the change in rope resistance. The average Young’s modulus and tensile strength obtained were 0.45±0.23 TPa and 1.72±0.64 GPa, respectively, which are lower than those calculated and measured previously. The factors that affect the mechanical strengths of nanotubes are discussed. © 1999 American Institute of Physics.
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62.20.D- Elasticity
62.20.F- Deformation and plasticity
81.05.ub Fullerenes and related materials

Enhanced photoluminescence in epitaxial ZnGa2O4:Mn thin-film phosphors using pulsed-laser deposition

Yong Eui Lee, David P. Norton, and John D. Budai

Appl. Phys. Lett. 74, 3155 (1999); http://dx.doi.org/10.1063/1.124095 (3 pages) | Cited 42 times

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The growth and properties of ZnGa2O4:Mn thin-film phosphors on single crystal substrates using pulsed-laser deposition were investigated. Epitaxial film properties were compared to polycrystalline films deposited on glass substrates. Green photoluminescence was observed for as-deposited films with no postannealing required. Enhanced luminescent intensity in the epitaxial films was observed as compared to randomly oriented polycrystalline films, suggesting that grain boundaries and grain alignment strongly influence the luminescent properties. The ratio of Zn/Ga in the films also affected photoluminescence properties, with strong green emission observed in Zn-deficient films. © 1999 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
78.66.Li Other semiconductors
81.15.Fg Pulsed laser ablation deposition
81.05.Hd Other semiconductors
68.55.-a Thin film structure and morphology
68.55.Nq Composition and phase identification

Temperature dependence of far-infrared electroluminescence in parabolic quantum wells

J. Ulrich, R. Zobl, K. Unterrainer, G. Strasser, E. Gornik, K. D. Maranowski, and A. C. Gossard

Appl. Phys. Lett. 74, 3158 (1999); http://dx.doi.org/10.1063/1.124091 (3 pages) | Cited 15 times

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We have measured the far-infrared emission from parabolically graded quantum wells driven by an in-plane electric field in the temperature range from 20 to 240 K. The peak emission corresponds to the intersubband plasmon in the parabolic potential. Its photon energy (6.6/9.8 meV) remains rather unaffected by temperature variations, the full-width at half-maximum ranges from 1 (T=20 K) to 2 meV (T=240 K). The reduction of emission efficiency with increasing temperature is attributed to the change in the nonradiative lifetime. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.60.Fi Electroluminescence
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Inversion of surface composition and evolution of nanostructure in Cu/Co nanocrystals

A. S. Edelstein, V. G. Harris, D. R. Rolison, L. Kurihara, David J. Smith, J. Perepezko, and M. H. da Silva Bassani

Appl. Phys. Lett. 74, 3161 (1999); http://dx.doi.org/10.1063/1.124087 (3 pages) | Cited 8 times

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Show Abstract
Nanocrystals of Cu/Co with a nearly pure Cu core and a Co-rich shell have been chemically synthesized. This structure results from reaction kinetics and represents an inversion of surface composition since the surface energy of Co is larger than that of Cu. Both the Cu core and the Co-rich shell initially have an fcc structure and a common lattice constant. Annealing at temperatures in the range of 300 to 600 °C causes the material to phase separate, forming small, increasingly pure Co nanocrystals which aggregate on the surface of the pure Cu nanocrystals. © 1999 American Institute of Physics.
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68.35.Dv Composition, segregation; defects and impurities
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.35.Md Surface thermodynamics, surface energies
61.46.-w Structure of nanoscale materials
61.72.Cc Kinetics of defect formation and annealing
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