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24 Nov 2003

Volume 83, Issue 21, pp. 4279-4450

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Appl. Phys. Lett. 83, 4294 (2003); http://dx.doi.org/10.1063/1.1629140 (3 pages)

Han-Youl Ryu, Masaya Notomi, and Yong-Hee Lee
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Enhancement of room-temperature photoluminescence in InAs quantum dots

W. Lu, Y. L. Ji, G. B. Chen, N. Y. Tang, X. S. Chen, S. C. Shen, Q. X. Zhao, and M. Willander

Appl. Phys. Lett. 83, 4300 (2003); http://dx.doi.org/10.1063/1.1623324 (3 pages) | Cited 14 times

Online Publication Date: 18 November 2003

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We report pronounced enhancement of room-temperature photoluminescence up to 80-fold induced by proton implantation and the rapid thermal annealing process in a multilayer InAs/GaAs quantum-dot structure. This effect is studied by a combination of material methods and resulted from both proton passivation and carrier capture enhancement effects. The maximum photoluminescence peak shift is about 23 meV, resulting from the intermixing of quantum dots. Linear dependence behavior as observed for both the nonradiative recombination time and carrier relaxation time on the ion-implantation dose. Maximum enhancement of the photoluminescence is observed for a proton implantation dose of 1.0×1014 cm−2 followed by rapid thermal annealing at 700 °C. These effects will be useful for quantum dot optoelectronic devices. © 2003 American Institute of Physics.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
61.72.uj III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors

Observation of a pseudogap at terahertz frequencies in the ferromagnetic metallic phase of La2−2xSr1+2xMn2O7 (x = 0.3)

Kouhei Takahashi, Noriaki Kida, and Masayoshi Tonouchi

Appl. Phys. Lett. 83, 4303 (2003); http://dx.doi.org/10.1063/1.1630152 (3 pages) | Cited 2 times

Online Publication Date: 18 November 2003

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We have directly measured the low-energy (0.5–3 meV) complex optical spectra of magnetoresistive La2−2xSr1+2xMn2O7 (x = 0.3) thin films by using THz time-domain spectroscopy. a-axis oriented thin films of La2−2xSr1+2xMn2O7 (x = 0.3) were epitaxially grown on MgO(100) substrates by pulsed laser deposition technique. The films showed paramagnetic insulator to ferromagnetic metal transition at 240 K. In the ferromagnetic metallic phase, we found that the real part of the optical conductivity spectrum exhibits a clear gap signature around 2 meV, which infringes the Drude-like behavior as expected from the electronic and magnetic properties. This provides an optical identification of a pseudogap in La2−2xSr1+2xMn2O7 (x = 0.3). © 2003 American Institute of Physics.
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75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
72.60.+g Mixed conductivity and conductivity transitions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Coordination and interface analysis of atomic-layer-deposition Al2O3 on Si(001) using energy-loss near-edge structures

K. Kimoto, Y. Matsui, T. Nabatame, T. Yasuda, T. Mizoguchi, I. Tanaka, and A. Toriumi

Appl. Phys. Lett. 83, 4306 (2003); http://dx.doi.org/10.1063/1.1629397 (3 pages) | Cited 25 times

Online Publication Date: 18 November 2003

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The coordination and interface of Al2O3 formed on Si(001) by atomic layer deposition (ALD) were studied using electron energy-loss spectroscopy in a transmission electron microscope. Al energy-loss near-edge structures (ELNESs) were interpreted using first-principles calculations. The Al L23 ELNESs show two peaks at 78.2 and 79.7 eV, which originate from tetrahedrally and octahedrally coordinated aluminum, respectively. The depth profile of coordination in ALD Al2O3/Si was investigated. While both tetrahedrally and octahedrally coordinated Al atoms exist in the ALD Al2O3, the former is dominant near the interface. Aluminum silicate was detected near the interface, and it may cause the difference in aluminum coordination. © 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
79.20.Uv Electron energy loss spectroscopy
68.37.Lp Transmission electron microscopy (TEM)
68.55.-a Thin film structure and morphology

Low-density polymer thin film formation in supercritical carbon dioxide

Tadanori Koga, Y.-S. Seo, J. L. Jerome, S. Ge, M. H. Rafailovich, J. C. Sokolov, B. Chu, O. H. Seeck, M. Tolan, and R. Kolb

Appl. Phys. Lett. 83, 4309 (2003); http://dx.doi.org/10.1063/1.1629799 (3 pages) | Cited 10 times

Online Publication Date: 18 November 2003

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We report a method for producing stable low-density polymer films by using supercritical carbon dioxide (scCO2). Two different molecular weight polystyrene films with various thicknesses were exposed to scCO2 along the density fluctuation ridge in P–T phase diagram. The swollen structures could be then frozen by flash evaporation of CO2 without forming additional voids. X-ray reflectivity data clearly showed that exposure to scCO2 could be used to produce uniform low-density films of about 2Rg thick or less, where Rg is radius of polymer gyration. © 2003 American Institute of Physics.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
68.55.-a Thin film structure and morphology
61.41.+e Polymers, elastomers, and plastics

Coordination of boron and phosphorous in borophosphosilicate glasses

R. Carboni, G. Pacchioni, M. Fanciulli, A. Giglia, N. Mahne, M. Pedio, S. Nannarone, and F. Boscherini

Appl. Phys. Lett. 83, 4312 (2003); http://dx.doi.org/10.1063/1.1629147 (3 pages) | Cited 9 times

Online Publication Date: 18 November 2003

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We report boron K-edge x-ray absorption near-edge structure measurements on borophosphosilicate glasses and density functional theory calculations aimed at determining the most stable local geometries for boron and phosphorous. We demonstrate that phosphorous induces a modification in the local structure of boron, from a trigonal to a tetrahedral geometry. The microscopic mechanisms involved are discussed. © 2003 American Institute of Physics.
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61.43.Fs Glasses
78.70.Dm X-ray absorption spectra
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.23.Cq Amorphous semiconductors, metallic glasses, glasses

Ion beam-induced anisotropic plastic deformation at 300 keV

T. van Dillen, A. Polman, C. M. van Kats, and A. van Blaaderen

Appl. Phys. Lett. 83, 4315 (2003); http://dx.doi.org/10.1063/1.1629793 (3 pages) | Cited 34 times

Online Publication Date: 18 November 2003

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Contrary to earlier predictions, ion irradiation at energies as low as 300 keV causes dramatic anisotropic plastic deformation of silica glass. Spherical colloidal silica particles with diameters of 125, 305, and 1030 nm were irradiated with Xe ions at energies in the range 0.3–4.0 MeV at temperatures between 85 and 380 K. Irradiation-induced anisotropic plastic deformation changes the colloid shape from spherical into oblate ellipsoidal at a rate that strongly increases with ion energy. At a fixed fluence, the transverse diameter increases with electronic energy loss. Even at an energy as low as 300 keV large particle anisotropy was found (size aspect ratio of 1.43 at 1×1015 cm−2). The transverse plastic strain gradually decreases with increasing irradiation temperature: it decreases by a factor 4.5 between 85 and 380 K. The data are in agreement with a viscoelastic thermal spike model for anisotropic deformation. © 2003 American Institute of Physics.
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61.80.Jh Ion radiation effects
61.82.Ms Insulators
81.05.Kf Glasses (including metallic glasses)
62.20.F- Deformation and plasticity
61.43.Fs Glasses
81.40.Lm Deformation, plasticity, and creep
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations

Doped thin films of two organic molecules for light-emitting diodes

Umberto Giovanella, Chiara Botta, Mariacecilia Pasini, William Porzio, and Silvia Destri

Appl. Phys. Lett. 83, 4318 (2003); http://dx.doi.org/10.1063/1.1630156 (3 pages)

Online Publication Date: 18 November 2003

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The photoluminescence and electroluminescence of doped organic materials are reported for thin films prepared by ultrahigh-vacuum coevaporation and by spin coating from solution of two emitting molecules. For both films, efficient energy transfer from the donor to the acceptor molecules is observed without relevant dopant segregation for molar concentrations up to 10%. In spin-coated films the energy transfer from the matrix to the dopant is due to purely resonant energy transfer processes while the cosublimated films show the presence of additional thermally activated hopping processes. Light-emitting diodes fabricated with coevaporated films yield electroluminescence with higher efficiency and stability. © 2003 American Institute of Physics.
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78.66.Qn Polymers; organic compounds
78.55.Kz Solid organic materials
78.60.Fi Electroluminescence
85.60.Jb Light-emitting devices

Smooth relaxed Si0.75Ge0.25 layers on Si(001) via in situ rapid thermal annealing

S. Hong, Y. L. Foo, K. A. Bratland, T. Spila, K. Ohmori, M. R. Sardela, J. E. Greene, and E. Yoon

Appl. Phys. Lett. 83, 4321 (2003); http://dx.doi.org/10.1063/1.1629792 (3 pages) | Cited 6 times

Online Publication Date: 18 November 2003

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Atomically flat, fully strained Si1−xGex layers with thicknesses ranging from 8 to 180 nm were grown on Si(001) at 450 °C by gas-source molecular beam epitaxy from Ge2H6/Si2H6 mixtures. We show that smooth, relaxed alloy layers are obtained, without the necessity of using several-microns-thick compositionally graded layers, via in situ rapid thermal annealing of fully strained Si1−xGex(001) layers at 1000 °C for 10 s. Relaxed Si0.75Ge0.25(001) layers with thicknesses of 100–180 nm were found to have surface widths of ≃5 nm, comparable to the best results obtained using thick graded buffer layers. © 2003 American Institute of Physics.
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81.05.Hd Other semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Cc Kinetics of defect formation and annealing
68.55.-a Thin film structure and morphology

Thermal stability of internal gettering of iron in silicon and its impact on optimization of gettering

Peng Zhang, Hele Väinölä, Andrei A. Istratov, and Eicke R. Weber

Appl. Phys. Lett. 83, 4324 (2003); http://dx.doi.org/10.1063/1.1630158 (3 pages) | Cited 7 times

Online Publication Date: 18 November 2003

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The redissolution behavior of gettered iron was studied in p-type Czochralski-grown silicon with a doping level of 2.5×1014 cm−3 and an oxide precipitate density of 5×109 cm−3. The concentrations of interstitial iron and iron–boron pairs were measured by deep level transient spectroscopy. It was found that the dependence of redissolved iron concentration on annealing time can be fitted by the function C(t) = C0[1−exp(−t/τdiss)], and the dissolution rate τdiss−1 has an Arrhenius-type temperature dependence of τdiss−1 = 4.01×104×exp[−(1.47±0.10) eV/kBT] s−1. Based on this empirical equation, we predict how stable the gettered iron is during different annealing sequences and discuss implications for optimization of internal gettering. © 2003 American Institute of Physics.
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61.72.Yx Interaction between different crystal defects; gettering effect
81.05.Cy Elemental semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.72.J- Point defects and defect clusters
81.10.Fq Growth from melts; zone melting and refining

In-plane polarization anisotropy and polarization rotation for M-plane GaN films on LiAlO2

Pranob Misra, Yue Jun Sun, Oliver Brandt, and Holger T. Grahn

Appl. Phys. Lett. 83, 4327 (2003); http://dx.doi.org/10.1063/1.1630168 (3 pages) | Cited 11 times

Online Publication Date: 18 November 2003

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We investigate the dependence of the transmittance spectra of strained M-plane GaN films on the angle of the linear in-plane polarization, with the c axis of the underlying wurtzite crystal structure in the film plane. Because of the reduced in-plane symmetry and the large in-plane anisotropic strain, the transmission spectra for an arbitrary in-plane polarization angle can be directly derived from two transitions with polarizations parallel and perpendicular to the c axis. Since the energy gap for these two polarizations is shifted by more than 50 meV, the M-plane GaN film becomes dichroic, resulting in a polarization rotation after transmission for energies between the two gaps for an initial angle of 45° by as much as 40° towards the c axis. © 2003 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.20.Ek Optical activity
78.40.Fy Semiconductors
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
71.20.Nr Semiconductor compounds

Patterning-based investigation of the length-scale dependence of the surface evolution during multilayer epitaxial growth

S. Shah, T. J. Garrett, K. Limpaphayom, T. Tadayyon-Eslami, H. C. Kan, and R. J. Phaneuf

Appl. Phys. Lett. 83, 4330 (2003); http://dx.doi.org/10.1063/1.1630170 (3 pages) | Cited 4 times

Online Publication Date: 18 November 2003

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We describe an investigation of the lateral length scale dependence of the evolution of topographical corrugations during multilayer molecular beam epitaxial growth in the GaAs/AlAs multilayer system. By patterning the substrate at series of well-defined spatial periods, we are able to study selectively the changes which occur as a function of lateral period over a wide range of corrugation amplitudes. A critical pattern period, which increases monotonically with thickness, separates an initial long spatial period regime where roughness is amplified, from a later, short spatial period regime in which the topography of the growing surface smoothes out. © 2003 American Institute of Physics.
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68.65.Ac Multilayers
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.07.-b Nanoscale materials and structures: fabrication and characterization
68.47.Fg Semiconductor surfaces
81.05.Ea III-V semiconductors
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