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27 Jan 2003

Volume 82, Issue 4, pp. 487-659

Issue Cover Spotlight Figure

Appl. Phys. Lett. 82, 559 (2003); http://dx.doi.org/10.1063/1.1539543 (3 pages)

P. R. C. Kent and Alex Zunger
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Highly efficient prism coupling to whispering gallery modes of a square μ cavity

Yong-Le Pan and Richard K. Chang

Appl. Phys. Lett. 82, 487 (2003); http://dx.doi.org/10.1063/1.1540242 (3 pages) | Cited 19 times

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By using prism coupling to a square μ cavity, over 75% energy transfer to the whispering gallery modes (Q>106) by frustrated total internal reflection was observed. A good comparison was found between measured data and theoretical model (based on a Fabry–Perot resonator), for the dependence of the coupling and linewidth of the whispering gallery modes (WGMs) as a function of relative separation between the prism and the μ cavity. By selecting the incident angle at the prism interface, the coupling to all four different sets of WGMs can be changed to coupling to only one set of WGMs. © 2003 American Institute of Physics.
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42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers
42.79.Bh Lenses, prisms and mirrors

Hybrid electro-optic polymer and selectively buried sol-gel waveguides

Y. Enami, G. Meredith, N. Peyghambarian, M. Kawazu, and A. K.-Y. Jen

Appl. Phys. Lett. 82, 490 (2003); http://dx.doi.org/10.1063/1.1539298 (3 pages) | Cited 14 times

Online Publication Date: 22 January 2003

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An approach to utilizing electro-optically (EO) active polymers in hybrid waveguide structures is described and demonstrated. Buried sol-gel waveguides provide a robust basis for planar integrated circuitry, suitable for coupling with optical fibers. By selectively exposing the core of a buried channel guide, overcoating with an EO polymer, and using appropriately tapered transition zones, a guided mode can be made to undergo adiabatic transitions from sol-gel waveguide up into the EO polymer and back. Such a single-mode device was constructed. These transitions were proven via modulation of the emerging wave’s polarization ellipse by application of voltage to the EO polymer. © 2003 American Institute of Physics.
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42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers
42.82.Cr Fabrication techniques; lithography, pattern transfer

High power light emission of IV–VI lead salt multiple-quantum-well structure grown by molecular-beam epitaxy on 〈111〉 BaF2 substrate

A. Majumdar, H. Z. Xu, S. Khosravani, F. Zhao, L. Jayasinghe, and Z. Shi

Appl. Phys. Lett. 82, 493 (2003); http://dx.doi.org/10.1063/1.1540238 (3 pages) | Cited 6 times

Online Publication Date: 22 January 2003

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Up to 4.9 W peak output power at room temperature and 61.5 W at 180 K were observed from photoluminescence of a PbSe/PbSrSe multiple-quantum-well (MQW) structure grown by molecular-beam epitaxy. Our theoretical calculation indicates that the lifted degeneracy of quantum-well structures on 〈111〉 orientation provides higher modal gain. This plus the improved epitaxial material quality of MQWs contribute to the high output power. The observed output powers are much higher than those of reported light emission of IV–VI lead salt materials. © 2003 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.07.St Quantum wells

Scattering polarizer with anisotropic crystals in a polyolefin polymer

Takamitsu Okumura, Takeshi Ishikawa, Yasuhiro Koike, and Akihiro Tagaya

Appl. Phys. Lett. 82, 496 (2003); http://dx.doi.org/10.1063/1.1540729 (3 pages) | Cited 3 times

Online Publication Date: 22 January 2003

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A scattering polarizer containing calcium carbonate whiskers (aragonite) in a polyolefin polymer has been developed. A selective multiple scattering technique, generating transmitted linearly polarized light and backward scattered light, has been demonstrated. A refractive index match and mismatch arises from the uniaxial orientation of the host polymer and the alignment of aragonite in the drawing direction. The dependence of the transmittance on the polarization direction of the incident light has been observed. The polarizing efficiency has been measured to be 60% with a 150-μm thickness. © 2003 American Institute of Physics.
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78.66.Qn Polymers; organic compounds
42.79.Wc Optical coatings
42.70.Jk Polymers and organics
81.05.Qk Reinforced polymers and polymer-based composites
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.35.+c Brillouin and Rayleigh scattering; other light scattering
81.10.Fq Growth from melts; zone melting and refining

High-Al-content crack-free AlGaN/GaN Bragg mirrors grown by molecular-beam epitaxy

F. Natali, D. Byrne, A. Dussaigne, N. Grandjean, J. Massies, and B. Damilano

Appl. Phys. Lett. 82, 499 (2003); http://dx.doi.org/10.1063/1.1539297 (3 pages) | Cited 25 times

Online Publication Date: 22 January 2003

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We report on the growth by molecular-beam epitaxy on 2 in. sapphire substrates of crack-free AlxGa1−xN/GaN distributed Bragg reflectors (DBRs) with high-Al composition (x = 0.5). This is achieved by introducing a thick AlN interlayer and strain mediating AlyGa1−yN layer between the substrate and DBR. The relatively larger refractive index ratio between Al0.5Ga0.5N and GaN permits one to obtain a quite large spectral stopband width (49 nm) and a high reflectance value (69%) for only eight mirror periods. © 2003 American Institute of Physics.
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42.79.Bh Lenses, prisms and mirrors
78.67.De Quantum wells
68.65.Fg Quantum wells
78.40.Fy Semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Three-color integration on rare-earth-doped GaN electroluminescent thin films

Y. Q. Wang and A. J. Steckl

Appl. Phys. Lett. 82, 502 (2003); http://dx.doi.org/10.1063/1.1539301 (3 pages) | Cited 36 times

Online Publication Date: 22 January 2003

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We have realized full color integration on rare-earth-doped thin-film electroluminescent (EL) GaN using lateral integration. Tm, Er, and Eu dopants were in situ doped into GaN thin films during growth in order to obtain blue, green, and red emission, respectively. Three color pixel arrays have been fabricated using spin-on-glass films as the sacrificial layers for lift-off lithography. The pixel dimensions are 0.2×0.7 mm2, and the separation is 0.2 mm. dc EL devices were fabricated using indium tin oxide transparent electrodes. Typical applied voltage was 30–40 V. The blue emission from Tm-doped GaN has a peak at 477 nm, the green emission from Er-doped GaN has two peaks at 537 and 558 nm, while the red emission from Eu-doped GaN has a peak at 621 nm. © 2003 American Institute of Physics.
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78.60.Fi Electroluminescence
78.66.Fd III-V semiconductors
71.55.Eq III-V semiconductors
71.20.Nr Semiconductor compounds

Linewidth enhancement factor of lattice-matched InGaNAs/GaAs quantum wells

Woon-Ho Seo and John F. Donegan

Appl. Phys. Lett. 82, 505 (2003); http://dx.doi.org/10.1063/1.1541097 (3 pages) | Cited 16 times

Online Publication Date: 22 January 2003

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The linewidth enhancement factors of lattice-matched 1.5 μm wavelength InGaNAs/GaAs and InGaAs/InP single-quantum-well structures are calculated using microscopic theory and 10×10 effective-mass Hamiltonian. InGaNAs/GaAs quantum wells have a lower threshold carrier density and higher differential gain resulting in a lower linewidth enhancement factor compared with InGaAs/InP quantum wells. For applications which require high gain and carrier densities, InGaNAs/GaAs quantum wells have a much lower linewidth enhancement factor over a temperature range 300–400 K. This lower value originates from the large electron effective mass caused by the nitrogen incorporation. The linewidth enhancement factor of InGaNAs is almost clamped as a function of carrier density and temperature compared with InGaAs. This effect is due to the enhanced match between conduction-valence band density of states and the improved electron confinement caused by the large conduction band offset and deep quantum wells. © 2003 American Institute of Physics.
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73.21.Fg Quantum wells
73.63.Hs Quantum wells
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Silver-coated silicon pillar photonic crystals: Enhancement of a photonic band gap

Vladimir Poborchii, Tetsuya Tada, Toshihiko Kanayama, and Alexander Moroz

Appl. Phys. Lett. 82, 508 (2003); http://dx.doi.org/10.1063/1.1541948 (3 pages) | Cited 24 times

Online Publication Date: 22 January 2003

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For a two-dimensional lattice of Si pillars it is shown both experimentally and theoretically that a photonic band gap for the light polarized perpendicular to pillars can be strongly enhanced by means of a silver coating of the pillars. A sizable omnidirectional photonic band gap is demonstrated for both square and triangular lattice of silver-coated Si pillars in the near-infrared and visible spectral range. © 2003 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
42.79.Wc Optical coatings
42.50.-p Quantum optics
78.30.Am Elemental semiconductors and insulators
78.40.Fy Semiconductors

Wavelength selectivities of organic photoconductive films: Dye-doped polysilanes and zinc phthalocyanine/tris-8-hydroxyquinoline aluminum double layer

S. Aihara, Y. Hirano, T. Tajima, K. Tanioka, M. Abe, N. Saito, N. Kamata, and D. Terunuma

Appl. Phys. Lett. 82, 511 (2003); http://dx.doi.org/10.1063/1.1541117 (3 pages) | Cited 21 times

Online Publication Date: 22 January 2003

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Organic photoconductors sensitive to blue, green, and red light were fabricated using coumarin 6 (C6)-doped poly(m-hexoxyphenyl)phenylsilane (PHPPS), rhodamine 6G (R6G)-doped polymethylphenylsilane (PMPS), and zinc phthalocyanine (ZnPc)/tris-8-hydroxyquinoline aluminum (Alq3) double layer, respectively. Selectivities of the spectral responses of these films were good enough to divide the incident light into three color components, indicating the possibility of color separation without prism for video cameras. The quantum efficiency of a ZnPc/Alq3 double-layer film is over an order of magnitude better than those of C6/PHPPS and R6G/PMPS blend films due to the dissociation of electron–hole pair generated at the interface between ZnPc and Alq3. © 2003 American Institute of Physics.
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73.61.Ph Polymers; organic compounds
72.40.+w Photoconduction and photovoltaic effects
78.66.Qn Polymers; organic compounds

Photoluminescence of metalorganic-chemical-vapor-deposition-grown GaInNAs/GaAs single quantum wells

M. O. Manasreh, D. J. Friedman, W. Q. Ma, C. L. Workman, C. E. George, and G. J. Salamo

Appl. Phys. Lett. 82, 514 (2003); http://dx.doi.org/10.1063/1.1540731 (3 pages) | Cited 5 times

Online Publication Date: 22 January 2003

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Photoluminescence (PL) spectra of interband transitions in GaInNAs/GaAs single quantum wells grown by metalorganic chemical vapor deposition on semi-insulating GaAs substrates were measured at 77 K for several samples grown with different In compositions and dimethylhydrazine (DMH)/III ratios. The results show that the PL intensity increases as the In mole fraction is increased from 0% to 25%, but the PL intensity is degraded for samples with an In mole fraction of 30% or higher. The peak position energies of the PL spectra were investigated as a function of the DMH/III ratio. Thermal annealing effect induced a blueshift in the PL spectra peak position energy in samples grown with high DMH/III ratios. © 2003 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.67.De Quantum wells
81.07.St Quantum wells
81.05.Ea III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing

Tunable femtosecond pulses in the near-ultraviolet from ultrabroadband parametric amplification

Pancho Tzankov, Torsten Fiebig, and Ivan Buchvarov

Appl. Phys. Lett. 82, 517 (2003); http://dx.doi.org/10.1063/1.1539555 (3 pages) | Cited 16 times

Online Publication Date: 22 January 2003

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Using an ultrabroadband amplification technique in a β-barium borate noncollinear optical parametric amplifier, pumped by the third harmonic of a 1 kHz Ti:sapphire laser, we generate tunable femtosecond pulses in the range of 335–480 nm with energies of a few hundred nJ. The developed setup is an amplification source with a bandwidth of more than 200 THz and provides femtosecond pulses in the near-ultraviolet spectral range using coherent amplification. Parts of the amplified white-light continuum spectrum were compressed to 24–35 fs using a prism pair. Further improvements could make it possible to generate tunable ultraviolet pulses as short as 4–5 fs. © 2003 American Institute of Physics.
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42.65.Lm Parametric down conversion and production of entangled photons
42.65.Yj Optical parametric oscillators and amplifiers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Fc Modulation, tuning, and mode locking

Photoluminescence from surfactant-assembled Y2O3:Eu nanotubes

Changfeng Wu, Weiping Qin, Guanshi Qin, Dan Zhao, Jisen Zhang, Shihua Huang, Shaozhe Lü, Huangqing Liu, and Haiyan Lin

Appl. Phys. Lett. 82, 520 (2003); http://dx.doi.org/10.1063/1.1542685 (3 pages) | Cited 70 times

Online Publication Date: 22 January 2003

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Y2O3:Eu nanotubes were fabricated by a surfactant assembly mechanism. The tubular structure was characterized by transmission electron microscopy. Under an ultraviolet-light excitation, the nanotubes show a relatively intense emission peak at 618 nm besides the 610 nm peak, different from that of single Y2O3:Eu nanocrystallites. The results of laser-selective excitation indicate that the emission centers near the surface of nanotube walls exhibit inhomogenously broadened spectra without spectral structures while the two sites (sites B and C) inside the nanotube walls present legible spectral structures. It is concluded by the number and peak positions of Stark levels that the sites B and C possess different site symmetries. © 2003 American Institute of Physics.
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78.67.Ch Nanotubes
78.55.Hx Other solid inorganic materials
78.20.Jq Electro-optical effects
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Effect of Ag photodoping on deep-level emission spectra of ZnO epitaxial films

Hyun-Yong Lee, Hang-Ju Ko, and Takafumi Yao

Appl. Phys. Lett. 82, 523 (2003); http://dx.doi.org/10.1063/1.1542676 (3 pages) | Cited 10 times

Online Publication Date: 22 January 2003

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Effect of Ag photodoping into ZnO films grown by molecular beam epitaxy has been examined via the real-time measurement of photoluminescence (PL) spectra using a HeCd laser at room temperature. While an asymmetric deep-level (green-yellow) broadband (D) is observed in PL of as-grown ZnO, it appears to change to two distinct bands (at 2.29 and 2.50 eV) in the illuminated Ag/ZnO. From the result of a Gaussian fitting, the yellow band at 2.29 eV is evaluated to relate with photodoped Ag atoms. With increasing the laser illumination time (photodoping), the PL intensity of broadband (ID) decreases and contrarily, the intensity of the near band edge emission observed at 3.297 eV (INB) shows a tendency to increase. We believe that the Ag can be photodoped into ZnO at 300 K and it contributes to the suppression of deep-level band, which results in an increase of INB. © 2003 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
73.20.Hb Impurity and defect levels; energy states of adsorbed species
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.uj III-V and II-VI semiconductors

Near-field optical lithography of a conjugated polymer

Robert Riehn, Ana Charas, Jorge Morgado, and F. Cacialli

Appl. Phys. Lett. 82, 526 (2003); http://dx.doi.org/10.1063/1.1539278 (3 pages) | Cited 62 times

Online Publication Date: 22 January 2003

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We report the fabrication of poly(p-phenylene vinylene) nanostructures by direct scanning near-field lithography of its soluble precursor. The technique is based on the spatially selective inhibition of the precursor solubility by exposure to the ultraviolet optical field present at the apex of scanning near-field fiber probes with aperture diameters between 40 and 80 nm (±5 nm). After development in methanol and thermal conversion under vacuum we obtain features with a minimum dimension of 160 nm. We demonstrate the use of the technique for the direct writing of two-dimensional photonic crystals with intentional defects and a periodicity relevant to applications in the visible range. Using a Bethe–Bouwkamp model, we then discuss the influence of probe size, tip-sample distance, and film thickness on the resolution of the lithographic process. We also discuss limitations to the resolution that can arise from physical properties of the lithographic medium. © 2003 American Institute of Physics.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
81.16.Nd Micro- and nanolithography
42.70.Qs Photonic bandgap materials
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Structure of direct-current microdischarge plasmas in helium

Prashanth S. Kothnur, Xiaohui Yuan, and Laxminarayan L. Raja

Appl. Phys. Lett. 82, 529 (2003); http://dx.doi.org/10.1063/1.1540246 (3 pages) | Cited 11 times

Online Publication Date: 22 January 2003

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A one-dimensional, self-consistent, continuum model is used to elucidate plasma phenomena in a parallel-plate dc microdischarge with a 250 μm gap at a pressure of 250 Torr. The microdischarge is found to have a bulk plasma region and a cathode sheath region with sizes that are comparable. Depending on the discharge current densities, peak electron densities of order up to 1014 cm−3 are predicted. Electron temperature of several eV are predicted within the cathode sheath while temperatures between 2 and 3 eV are observed in the bulk plasma. Gas temperatures of the order of 1000 K are predicted, emphasizing the importance of gas heating phenomena in dc microdischarges. © 2003 American Institute of Physics.
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52.80.-s Electric discharges
52.20.-j Elementary processes in plasmas
52.40.Kh Plasma sheaths
52.25.Kn Thermodynamics of plasmas
52.70.-m Plasma diagnostic techniques and instrumentation
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Correlation between the photoluminescence lifetime and defect density in bulk and epitaxial ZnO

T. Koida, S. F. Chichibu, A. Uedono, A. Tsukazaki, M. Kawasaki, T. Sota, Y. Segawa, and H. Koinuma

Appl. Phys. Lett. 82, 532 (2003); http://dx.doi.org/10.1063/1.1540220 (3 pages) | Cited 86 times

Online Publication Date: 22 January 2003

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Influences of point defects on the nonradiative processes in ZnO were studied using steady-state and time-resolved photoluminescence (PL) spectroscopy making a connection with the results of positron annihilation measurement. Free excitonic PL intensity naturally increased with the increase in the nonradiative PL lifetime (τnr). Density or size of Zn vacancies (VZn) decreased and τnr increased with increasing growth temperature in heteroepitaxial films grown on a ScAlMgO4 substrate. Use of homoepitaxial substrate further decreased the VZn density. However, τnr was the shortest for the homoepitaxial film; i.e., no clear dependence was found between τnr and density / size of VZn or positron scattering centers. The results indicated that nonradiative recombination processes are not solely governed by single point defects, but by certain defect species introduced by the presence of VZn such as vacancy complexes. © 2003 American Institute of Physics.
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78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
71.55.Gs II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.J- Point defects and defect clusters
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.47.-p Spectroscopy of solid state dynamics
78.70.Bj Positron annihilation

Effect of surfaces on the size-dependent elastic state of nano-inhomogeneities

P. Sharma, S. Ganti, and N. Bhate

Appl. Phys. Lett. 82, 535 (2003); http://dx.doi.org/10.1063/1.1539929 (3 pages) | Cited 207 times

Online Publication Date: 22 January 2003

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The effect of surface energies, strains, and stresses on the size-dependent elastic state of embedded inhomogeneities are investigated. At nanolength scales, due to the increasing surface-to-volume ratio, surface effects become important and induce a size dependency in the otherwise size-independent classical elasticity solutions. In this letter, closed-form expressions are derived for the elastic state of eigenstrained spherical inhomogeneities with surface effects using a variational formulation. Our results indicate that surface elasticity can significantly alter the fundamental nature of stress state at nanometer length scales. Additional applications of our work on nanostructures such as quantum dots, composites, etc. are implied. © 2003 American Institute of Physics.
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62.25.-g Mechanical properties of nanoscale systems
61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
68.35.Gy Mechanical properties; surface strains
62.20.D- Elasticity
68.35.Md Surface thermodynamics, surface energies

Blue-light emission from sputtered Si:SiO2 films without annealing

Osamu Hanaizumi, Kazutaka Ono, and Yuichi Ogawa

Appl. Phys. Lett. 82, 538 (2003); http://dx.doi.org/10.1063/1.1539302 (3 pages) | Cited 18 times

Online Publication Date: 22 January 2003

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We observed a photoluminescence (PL) spectrum at room temperature that had a peak with full width of half maximum (FWHM) of 0.38 eV near the band gap energy of 3.2 eV from a Si:SiO2 sputtered film without annealing. Blue-light emission could be seen by the naked eye. A low-intensity PL peak with FWHM of 0.20 eV was also observed at around 1.6 eV. We have already demonstrated that our method automatically forms Si clusters contributing to visible emission. Our results did not contradict the well-founded conjecture that there were two mechanisms of emission from Si clusters: emission at 1.6–1.7 eV due to the surface state of the oxidized Si nanocrystals and emission at the band gap energy originating from the quantum confinement effect. © 2003 American Institute of Physics.
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78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
78.40.Fy Semiconductors
81.15.Cd Deposition by sputtering

Spin injection through different g-factor heterointerfaces using negative trions for spin detection

M. Ghali, J. Kossut, and W. Heiss

Appl. Phys. Lett. 82, 541 (2003); http://dx.doi.org/10.1063/1.1540219 (3 pages) | Cited 3 times

Online Publication Date: 22 January 2003

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We demonstrate using the formation and the optical signatures of negatively charged excitonic complexes, trions, as a sensitive detector for spin injection. In our study, spin-polarized electrons are optically injected from a Cd0.97Mn0.03Te spin aligning layer to CdTe quantum well (QW) via a nonmagnetic Cd0.98Mg0.02Te spacer. In photoluminescence measurements, for the excitation above the Cd0.97Mn0.03Te band gap, we find a gradual change in the circular polarization of the trion emission from a negative value at low magnetic fields to a positive one at high fields with a transition at B ∼ 3 T. This polarization behavior is in contrast to that for selective excitation below the spin aligner band gap and evidences unambiguously a redistribution of the electron spin population between the electron Zeeman sublevels in the QW due the spin injection of effectively polarized electrons from the magnetic spin injector. © 2003 American Institute of Physics.
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72.25.Mk Spin transport through interfaces
71.35.Pq Charged excitons (trions)
73.21.Fg Quantum wells
78.67.De Quantum wells
73.63.Hs Quantum wells
72.25.Dc Spin polarized transport in semiconductors
78.55.Et II-VI semiconductors
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
78.20.Ls Magneto-optical effects

Small angle x-ray scattering for measuring pore-size distributions in porous low-κ films

K. Omote, Y. Ito, and S. Kawamura

Appl. Phys. Lett. 82, 544 (2003); http://dx.doi.org/10.1063/1.1539546 (3 pages) | Cited 24 times

Online Publication Date: 22 January 2003

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A small-angle x-ray scattering technique has been applied for characterizing pore-size distribution in porous low-κ dielectric films. The data are collected in reflection geometry using offset θ/2θ scans for avoiding strong specular reflections from the film surface and its substrate. The effects of refraction and reflection at the film surface and interface are corrected by the distorted wave Born approximation. A Γ-distribution mode is used to determine the pore-size distribution in a film. The technique has been used to analyze porous methyl silsesquioxane films. The pore sizes were found to disperse in the range from subnanometer to several nanometers, and the results agree well with those obtained by the N2 gas adsorption technique. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.05.Rm Porous materials; granular materials
77.55.-g Dielectric thin films
78.70.Ck X-ray scattering
77.84.Jd Polymers; organic compounds

Pyramidal-plane ordering in AlGaN alloys

M. Benamara, L. Kirste, M. Albrecht, K. W. Benz, and H. P. Strunk

Appl. Phys. Lett. 82, 547 (2003); http://dx.doi.org/10.1063/1.1541093 (3 pages) | Cited 10 times

Online Publication Date: 22 January 2003

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This letter reports the identification of long-range ordering in AlGaN compounds along the pyramidal planes by transmission electron microscopy. This ordering consists of the alternate stacking of GaN and AlN layers on {1math01} planes and is evidenced by the comparison of experimental diffraction patterns along [01math0] and [11math0] with calculated patterns. A formation model of this ordering is presented. It is based upon Ga incorporation on reduced-N coordination sites that are located at step edges on {1math01} pit facets. © 2003 American Institute of Physics.
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61.66.Fn Inorganic compounds
81.05.Ea III-V semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.47.Fg Semiconductor surfaces
61.05.jm Convergent-beam electron diffraction, selected-area electron diffraction, nanodiffraction
68.37.Lp Transmission electron microscopy (TEM)

White light emission from single component polymers fabricated by spin coating

Mu-Lin Tsai, Ching-Yang Liu, Ming-Ann Hsu, and Tahsin J. Chow

Appl. Phys. Lett. 82, 550 (2003); http://dx.doi.org/10.1063/1.1540247 (3 pages) | Cited 43 times

Online Publication Date: 22 January 2003

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A polymeric material prepared from single monomers is described, which emits white electroluminescence. The broad emission band is composed of a blue emission from anthracene and a red emission from aggregates. Single and double layer devices of light emitting diode were fabricated and examined. © 2003 American Institute of Physics.
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78.60.Fi Electroluminescence
85.60.Jb Light-emitting devices
78.66.Qn Polymers; organic compounds
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
42.70.Jk Polymers and organics

Formation and optical properties of InAs/GaAs quantum dots for applications as infrared photodetectors operating at room temperature

M. D. Kim, S. K. Noh, S. C. Hong, and T. W. Kim

Appl. Phys. Lett. 82, 553 (2003); http://dx.doi.org/10.1063/1.1540733 (3 pages) | Cited 12 times

Online Publication Date: 22 January 2003

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The formation and optical properties of lateral quantum-dot infrared photodetector (QDIP) structures utilizing uniform-sized InAs QDs obtained by controlling the intensity of the reflection high-energy diffraction pattern and the As/In flux ratio were investigated. The thickness of the pseudomorphic, strained InAs wetting layer increased slightly with decreasing As/In flux ratio. The characteristic peaks corresponding to the interband and the intersubband transitions were observed, respectively, in the photoluminescence and Fourier transform infrared spectra. The absorption spectrum showed an absorption peak corresponding to the intersubband transition at around 10 μm. These results indicate that InAs/GaAs QDs obtained by controlling growth conditions hold promise for potential applications in QDIP devices operating at room temperature. © 2003 American Institute of Physics.
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78.67.Hc Quantum dots
85.60.Gz Photodetectors (including infrared and CCD detectors)
81.07.Ta Quantum dots
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
68.37.Ps Atomic force microscopy (AFM)
78.55.Cr III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Direct evidence for grain-boundary depletion in polycrystalline CdTe from nanoscale-resolved measurements

Iris Visoly-Fisher, Sidney R. Cohen, and David Cahen

Appl. Phys. Lett. 82, 556 (2003); http://dx.doi.org/10.1063/1.1542926 (3 pages) | Cited 24 times

Online Publication Date: 22 January 2003

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We use scanning probe microscopy-based methods for direct characterization of a single grain boundary and a single grain surface in solar cell-quality CdTe, deposited by closed-space vapor transport. We find that scanning capacitance microscopy can serve to study polycrystalline electronic materials, notwithstanding the strong topographical variations. In this way, we find a barrier for hole transport across grain boundaries, a conclusion supported by the much more topography-sensitive scanning kelvin probe microscopy, with some variation in barrier height between different boundaries. © 2003 American Institute of Physics.
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61.72.Mm Grain and twin boundaries
68.47.Fg Semiconductor surfaces
68.37.Ps Atomic force microscopy (AFM)
84.60.Jt Photoelectric conversion
68.35.B- Structure of clean surfaces (and surface reconstruction)

Failure of nitrogen cluster states to emerge into the bandgap of GaAsN with application of pressure

P. R. C. Kent and Alex Zunger

Appl. Phys. Lett. 82, 559 (2003); http://dx.doi.org/10.1063/1.1539543 (3 pages) | Cited 25 times

Online Publication Date: 22 January 2003

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The electronic structure of GaAsN alloys was previously described in terms of nitrogen “cluster states” (CS) that exist in the dilute alloy in the bandgap, and “perturbed host states” (PHS) inside the conduction band. As the nitrogen concentration increases, the PHS plunge down in energy overtaking the CS. We show theoretically that the CS respond to the application of pressure in two different ways: the highly localized deep CS emerge (or remain) in the gap, because their pressure coefficient is lower than that of the conduction band minimum. In contrast, the shallow CS (first to be overtaken) hybridize so strongly with the conduction band that their pressure coefficient becomes comparable to that of the conduction states. These states fail to emerge into the gap upon application of pressure because they move, with application of pressure, at a similar rate with conduction states. © 2003 American Institute of Physics.
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71.20.Nr Semiconductor compounds
81.05.Ea III-V semiconductors
71.55.Eq III-V semiconductors
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
62.50.-p High-pressure effects in solids and liquids
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