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5 May 2003

Volume 82, Issue 18, pp. 2939-3130

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Appl. Phys. Lett. 82, 2957 (2003); http://dx.doi.org/10.1063/1.1571977 (3 pages)

Tadashi Kawazoe, Kiyoshi Kobayashi, Suguru Sangu, and Motoichi Ohtsu
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Polarized Raman scattering of impurity modes in beryllium-doped cubic boron nitride single crystals

Kenji Watanabe, Takashi Taniguchi, Hisao Kanda, and Elena M. Shishonok

Appl. Phys. Lett. 82, 2972 (2003); http://dx.doi.org/10.1063/1.1569989 (3 pages) | Cited 4 times

Online Publication Date: 29 April 2003

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Impurity-induced modes at 212 and 535 cm−1 have been studied by using Raman scattering spectroscopy in Be-doped cubic boron nitride single crystals, which have been grown by the temperature-gradient method under high pressure. Those bands show prominent polarization properties of T2 and A1 modes for the 212 and 535 cm−1 bands, respectively. Based on the polarization properties and a simple calculation of a molecular model, the origin of the bands is explained by postulating resonance modes of substitutional Be with a weak force constant between the host atoms and the Be. Anomalies of a forbidden transverse optical mode and the T2 mode due to phonon–plasma coupling caused by photoexcited free carriers have been also observed in high excitation density. © 2003 American Institute of Physics.
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63.20.Pw Localized modes
63.20.kk Phonon interactions with other quasiparticles
78.30.Fs III-V and II-VI semiconductors

White light emission from radical carbonyl-terminations in Al2O3–SiO2 porous glasses with high luminescence quantum efficiencies

Tomokatsu Hayakawa, Ai Hiramitsu, and Masayuki Nogami

Appl. Phys. Lett. 82, 2975 (2003); http://dx.doi.org/10.1063/1.1569038 (3 pages) | Cited 25 times

Online Publication Date: 29 April 2003

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Development of white phosphors with highly emissive, stable, and less toxic characteristics has been important for display and lighting technology. In this letter, it is shown that sol-gel-derived glasses of aluminosilicate composition, followed by a heat treatment in air at low temperatures around 500 °C, exhibit two intense, visible photoluminescence bands: One is due to point defects in these glasses and the other comes from radical carbonyl-terminations on the surface of pores. The photoluminescence provides a white light with high luminescence quantum efficiency (∼66.5%) under long-wavelength ultraviolet excitation. © 2003 American Institute of Physics.
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78.55.Mb Porous materials
78.55.Qr Amorphous materials; glasses and other disordered solids
42.70.Ce Glasses, quartz
81.05.Kf Glasses (including metallic glasses)
81.10.Dn Growth from solutions
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)
81.05.Rm Porous materials; granular materials

Growth and physical properties of Ga2O3 thin films on GaAs(001) substrate by molecular-beam epitaxy

Z. Yu, C. D. Overgaard, R. Droopad, M. Passlack, and J. K. Abrokwah

Appl. Phys. Lett. 82, 2978 (2003); http://dx.doi.org/10.1063/1.1572478 (3 pages) | Cited 27 times

Online Publication Date: 29 April 2003

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We report effusive evaporation of Ga2O3 thin films on GaAs(001) substrates in a production-type molecular-beam epitaxy system. A polycrystalline Ga2O3 charge heated in a high-temperature effusion cell is used as the evaporation source. The Ga2O3–GaAs structures are characterized by atomic force microscopy (AFM), Rutherford backscattering spectroscopy (RBS), ellipsometry, and transmission electron microscopy (TEM). The Ga2O3 films are amorphous and stoichiometric by transmission electron diffraction and RBS, respectively. Under optimal growth conditions, the Ga2O3 film surface has a typical roughness of 2–3 Å as revealed by AFM, while the Ga2O3–GaAs interface is atomically abrupt as confirmed by the cross-sectional TEM. Such amorphous and stoichiometric Ga2O3 oxide paves the way for GaAs gate dielectrics applications. © 2003 American Institute of Physics.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.37.Ps Atomic force microscopy (AFM)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.37.Lp Transmission electron microscopy (TEM)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Ct Interface structure and roughness

Identification of hexagonal polycrystal in epitaxially grown InN by synchrotron x-ray diffraction and near-edge x-ray absorption fine structure spectroscopy

Ik Jae Lee, Hyun-Joon Shin, Suk Sang Chang, Min Kyu Lee, and Hyung-Kook Kim

Appl. Phys. Lett. 82, 2981 (2003); http://dx.doi.org/10.1063/1.1572475 (3 pages) | Cited 2 times

Online Publication Date: 29 April 2003

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The structures and crystallographic orientations of indium nitride films of varying thicknesses on sapphire(0001) were investigated using high-resolution synchrotron x-ray scattering and angle-dependent near-edge x-ray absorption fine structure (NEXAFS) spectroscopy with linearly polarized x rays. The x-ray scattering data showed that epitaxially grown InN films have a polycrystalline structure when their thickness is greater than 3000 Å. The N 1s NEXAFS spectra of thin films have a strong polarization-dependent spectral feature resulting from the preferred c-axis orientation. This polarization dependence decreases as the film thickness increases and is not present in the spectra of films that are more than 3000 Å thick. These results indicate that the c axis has a preferred orientation in thin films, but that this orientation is random in thick films, which have a polycrystalline hexagonal structure. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
78.70.Dm X-ray absorption spectra
61.05.cp X-ray diffraction

A valence electron concentration criterion for glass-formation ability of metallic liquids

Q. Jiang, B. Q. Chi, and J. C. Li

Appl. Phys. Lett. 82, 2984 (2003); http://dx.doi.org/10.1063/1.1571984 (3 pages) | Cited 12 times

Online Publication Date: 29 April 2003

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Critical cooling rate of a metallic liquid (Rc) necessary to form glass is correlated to the valence concentration e/a of the liquid (e and a denote valence and atom number in a unit cell, respectively). Rc of liquid is minimized at e/a = 3.5. The principles of the composition design to form bulk metallic glasses are as follows: e/a = 3.5, the component number (n) in the alloy is larger than three, and the component percentage of the ith component (xi) approaches 1/n. © 2003 American Institute of Physics.
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64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
61.43.Fs Glasses

Carrier lifetime studies of deeply penetrating defects in self-ion implanted silicon

D. H. Macdonald, H. Maeckel, S. Doshi, W. Brendle, A. Cuevas, J. S. Williams, and M. J. Conway

Appl. Phys. Lett. 82, 2987 (2003); http://dx.doi.org/10.1063/1.1572469 (3 pages) | Cited 3 times

Online Publication Date: 29 April 2003

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Carrier lifetime measurements have been used to characterize residual defects after low-energy implanting of silicon ions followed by high-temperature annealing (900 or 1000 °C). The implant was found to result in two distinct regions of lifetime-reducing damage. First, a high recombination region, most likely due to stable dislocation loops, remained near the surface. In addition, deeply propagated defects, which were not present prior to annealing, were also detected. These deep defects, which are possibly silicon interstitials, diffuse so rapidly during annealing that their distribution becomes effectively uniform to a depth of 100 microns. Annealing at higher temperatures was found to reduce the severity of both the surface and the deeply propagated defects. © 2003 American Institute of Physics.
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61.72.uf Ge and Si
61.80.Jh Ion radiation effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.82.Fk Semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.72.Lk Linear defects: dislocations, disclinations

Influence of MgO substrate miscut on domain structure of pulsed laser deposited SrxBa1−xNb2O6 as characterized by x-ray diffraction and spectroscopic ellipsometry

C. M. Rouleau, G. E. Jellison, and D. B. Beach

Appl. Phys. Lett. 82, 2990 (2003); http://dx.doi.org/10.1063/1.1572464 (3 pages) | Cited 9 times

Online Publication Date: 29 April 2003

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Pulsed laser deposition has been used to grow highly oriented SrxBa1−xNb2O6 (SBN:x) on (001)MgO and miscut MgO (2° off 001 toward 100) in the presence of a pulsed O2 jet. The target stoichiometry was SBN:52±1.5%, but films grown at 700 °C were cation deficient and had a final composition of SBN:61±1.5%. Visually, the films were specular, but spectroscopic ellipsometry measurements showed they were highly absorbing, requiring a short anneal in O2 at 700 °C to make them fully transparent. Pole figure analysis indicated that a thick 626±1 nm film consisted of the characteristic antiphase domain structure of SBN, but four antiphase domains were found in a thin 185±1 nm film. However, the formation of these additional domains was suppressed in a 165±1 nm film grown on miscut MgO. Spectroscopic ellipsometry measurements have been made to measure surface and interface roughness, film thickness, as well as the spectroscopic refractive index and extinction coefficient of the films. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
81.15.Fg Pulsed laser ablation deposition
77.80.-e Ferroelectricity and antiferroelectricity
78.66.Nk Insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Ct Interface structure and roughness

Dielectric function of nanocrystalline silicon with few nanometers (<3 nm) grain size

Maria Losurdo, Maria Michela Giangregorio, Pio Capezzuto, Giovanni Bruno, M. F. Cerqueira, E. Alves, and M. Stepikhova

Appl. Phys. Lett. 82, 2993 (2003); http://dx.doi.org/10.1063/1.1569052 (3 pages) | Cited 32 times

Online Publication Date: 29 April 2003

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The dielectric function of nanocrystalline silicon (nc-Si) with crystallite size in the range of 1 to 3 nm has been determined by spectroscopic ellipsometry in the range of 1.5 to 5.5 eV. A Tauc–Lorentz parameterization is used to model the nc-Si optical properties. The nc-Si dielectric function can be used to analyze nondestructively nc-Si thin films where nanocrystallites cannot be detected by x-ray diffraction and Raman spectroscopy. © 2003 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)
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
78.66.Db Elemental semiconductors and insulators
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Very efficient light emission from bulk crystalline silicon

Thorsten Trupke, Jianhua Zhao, Aihua Wang, Richard Corkish, and Martin A. Green

Appl. Phys. Lett. 82, 2996 (2003); http://dx.doi.org/10.1063/1.1572473 (3 pages) | Cited 70 times

Online Publication Date: 29 April 2003

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Due to its indirect bandstructure, bulk crystalline silicon is generally regarded as a poor light emitter. In contrast to this common perception, we report here on surprisingly large external photoluminescence quantum efficiencies of textured bulk crystalline silicon wafers of up to 10.2% at T = 130 K and of 6.1% at room temperature. Using a theoretical model to calculate the escape probability for internally generated photons, we can conclude from these experimental figures that the radiative recombination probability or internal luminescence quantum efficiency exceeds 20% at room temperature. © 2003 American Institute of Physics.
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78.55.Ap Elemental semiconductors

CuAu-I-type ordered structures in InxAl1−xAs epilayers grown on (001) InP substrates

Ho Seong Lee and Jeong Yong Lee

Appl. Phys. Lett. 82, 2999 (2003); http://dx.doi.org/10.1063/1.1572535 (3 pages) | Cited 2 times

Online Publication Date: 29 April 2003

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Transmission electron microscopy (TEM) measurements were carried out to investigate the spontaneously ordered structure in InxAl1−xAs epitaxial layers grown on (001) InP substrates. The selected area diffraction pattern showed two sets of superstructure reflections with symmetrical intensity at (100) and (010) positions, indicating that CuAu-I-type ordered structures with two different variants were formed in the InxAl1−xAs epitaxial layers. The dark-field TEM image showed that the size of the CuAu-I-type ordered domains with a needle-like shape was approximately 3 ∼ 4 nm thick, with lengths ranging from 10 to 20 nm. Based on the TEM results, explanations are given to describe the formation of only two variants of CuAu-I-type ordering. © 2003 American Institute of Physics.
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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)

Observation of a hydrogenic donor in the luminescence of electron-irradiated GaN

Qing Yang, Henning Feick, and Eicke R. Weber

Appl. Phys. Lett. 82, 3002 (2003); http://dx.doi.org/10.1063/1.1570943 (3 pages) | Cited 14 times

Online Publication Date: 29 April 2003

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Excitonic luminescence of GaN after irradiation with 0.42-MeV electrons has been investigated in detail. The low-energy irradiation generates damage exclusively in the N sublattice. Additional bound-exciton lines are found and are shown to arise from a hydrogenic donor with a binding energy of 25 meV. The donor binding energy, bound-exciton localization energy, and bound-exciton lifetime are discussed in comparison with the values observed for ON and SiGa in the same sample. Nitrogen vacancies VN forming a hydrogenic donor state are suggested to be the most likely origin of this luminescence emission. Finally, a metastable behavior related to the damage-induced defects is reported and discussed in conjunction with interstitial-nitrogen-related defects. © 2003 American Institute of Physics.
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71.55.Eq III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
61.72.J- Point defects and defect clusters

Boundary migration in Zn bicrystal induced by a high magnetic field

A. D. Sheikh-Ali, D. A. Molodov, and H. Garmestani

Appl. Phys. Lett. 82, 3005 (2003); http://dx.doi.org/10.1063/1.1572536 (3 pages) | Cited 16 times

Online Publication Date: 29 April 2003

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A bicrystal of Zn with an originally flat 89° 〈10math0〉 symmetric tilt boundary was annealed in a magnetic field of 25 T. The boundary migrated under the action of a magnetic driving force in the direction of the grain with higher diamagnetic susceptibility. In addition, the boundary changed its crystallographic orientation, decreasing length and becoming almost perpendicular to the free surfaces. The results were interpreted in terms of magnetically forced grain boundary motion due to the anisotropy of the magnetic susceptibility in Zn. The absolute boundary mobility was measured to be about 5.1×10−9 m4/J s. © 2003 American Institute of Physics.
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61.72.Mm Grain and twin boundaries
75.20.En Metals and alloys
75.80.+q Magnetomechanical effects, magnetostriction

Improved photoluminescence of InGaAsN–(In)GaAsP quantum well by organometallic vapor phase epitaxy using growth pause annealing

Nelson Tansu, Jeng-Ya Yeh, and Luke J. Mawst

Appl. Phys. Lett. 82, 3008 (2003); http://dx.doi.org/10.1063/1.1572470 (3 pages) | Cited 16 times

Online Publication Date: 29 April 2003

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The metalorganic chemical vapor deposition of a highly strained InGaAsN quantum-well (QW) surrounded by (In)GaAsP direct barrier layers is investigated. We found that growth pause annealing with AsH3, performed immediately before and after the growth of the QW, significantly improves the optical quality of InGaAsN QW with (In)GaAsP direct barriers. The utilization of larger band gap barrier materials, such as InGaAsP or GaAsP, will potentially lead to reduced carrier leakage from the QW laser structures. © 2003 American Institute of Physics.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.55.Cr III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
78.67.De Quantum wells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors
68.65.Fg Quantum wells
81.07.St Quantum wells

Selective oxidation behavior of W/WN/polycrystalline-Si1−xGex gate structure in H2O+H2 ambient

Tae-Hang Ahn, In-Seok Yeo, Joong-Jung Kim, Jae-Sung Roh, and Jung-Ho Lee

Appl. Phys. Lett. 82, 3011 (2003); http://dx.doi.org/10.1063/1.1572961 (3 pages)

Online Publication Date: 29 April 2003

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Selective oxidation behavior, i.e., oxidation of polycrystalline-Si1−xGex (poly-SiGe) without metal oxidation, of the W/WN/poly-SiGe structure was investigated for gate electrode applications. While the dry oxidized samples showed a dramatic increase of the oxidation rate with increasing Ge content, the oxidation rate in the selectively oxidized (in a H2O+H2 ambient) samples was found to be very low irrespective of the Ge content. The oxides grown in a H2O+H2 ambient are identified to be only SiO2 even up to 60% Ge, other than the dry oxidized samples that consist of nearly pure SiO2 underneath a mixed oxide alloy of (Si,Ge)Ox. Different oxidation mechanisms based on the competition between the oxidation rate and the Ge diffusion rate in Si are suggested to explain a remarkable difference in the oxide thickess and composition. For dependable applications of poly-SiGe in metal-shunted gate structures, this oxidation feature enables a very clean sidewall profile with an improved reliability of gate oxides after selective oxidation process. © 2003 American Institute of Physics.
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81.65.Mq Oxidation
66.30.J- Diffusion of impurities

Dependence of morphology on miscut angle for Si(111) etched in NH4F

Joseph Fu, Hui Zhou, John Kramar, Richard Silver, and Satoshi Gonda

Appl. Phys. Lett. 82, 3014 (2003); http://dx.doi.org/10.1063/1.1569426 (3 pages) | Cited 3 times

Online Publication Date: 29 April 2003

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Hydrogen-terminated silicon surfaces are important and commonly used in several nanotechnology applications. A significant obstacle to their widespread use has been the repeatable preparation of large, flat surfaces. Using scanning probe microscopy, we have examined the surfaces of several vicinal Si(111) samples, with miscut angles ranging from 1.1° to 0.01°, produced by etching in a NH4F aqueous solution. Although the miscut angle sets the nominal terrace width, we have found that with wet chemical etch processing, as the vicinal angle decreases, the terrace width increases only to a maximum of ∼200 nm, limited by the etching anisotropy. The result is that for miscut angles below a critical angle, the surface roughness actually increases. © 2003 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
81.65.Cf Surface cleaning, etching, patterning
68.37.Ps Atomic force microscopy (AFM)
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