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9 Jun 2003

Volume 82, Issue 23, pp. 4011-4195

Issue Cover Spotlight Figure

Appl. Phys. Lett. 82, 4160 (2003); http://dx.doi.org/10.1063/1.1580641 (3 pages)

Eva M. Höhberger, Tomas Krämer, Werner Wegscheider, and Robert H. Blick
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AlGaInP/mirror/Si light-emitting diodes with vertical electrodes by wafer bonding

R. H. Horng, S. H. Huang, D. S. Wuu, and C. Y. Chiu

Appl. Phys. Lett. 82, 4011 (2003); http://dx.doi.org/10.1063/1.1579132 (3 pages) | Cited 4 times

Online Publication Date: 2 June 2003

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In a previous study, we reported a highly efficient AlGaInP light-emitting diode (LED) with a Au/AuBe/SiO2/Si mirror substrate (MS) fabricated by wafer bonding, where a planar electrode structure is used. In view of the more efficient epilayer area utilized, AlGaInP/mirror/barrier/Si LEDs with vertical electrodes are proposed in this work. A variety of barrier layers (Pt/Ti, TaN/Ta, and TiN/Ti) have been incorporated into the mirror structure. The mirror quality after bonding is a confirmed key issue in obtaining vertical MS–LEDs with high brightness. It is found that AuBe thickness has a large effect on the final MS–LED performance due to the difference in the interdiffusion of Be atoms in each mirror structure. The diffusion of excess Be atoms diffusing to the mirror side results in a rougher surface and inferior reflectivity. The luminance intensity of an AlGaInP LED chip (626 nm) with an optimum AuBe thickness can reach a maximum of ∼ 165 mcd at 20 mA with a forward voltage of 2.1 V. After encapsulation into lamps, the peak power efficiency can reach 21.7%, which corresponds to a 9 mW output at 20 mA. Therefore, the MS structure can be extended to fabricate high-brightness AlGaInP LEDs on Si with conventional vertical electrodes. © 2003 American Institute of Physics.
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85.60.Jb Light-emitting devices
68.35.Fx Diffusion; interface formation
78.66.Fd III-V semiconductors
78.66.Db Elemental semiconductors and insulators

Ultrafast sampling measurements using the photomodulated kinetic inductance in high-Tc superconductors

C. J. Stevens, G. Bianchi, and J. F. Ryan

Appl. Phys. Lett. 82, 4014 (2003); http://dx.doi.org/10.1063/1.1576905 (3 pages) | Cited 2 times

Online Publication Date: 2 June 2003

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We provide a demonstration of ultrafast sampling measurements using the photokinetic effect in high-Tc superconductors to observe fast electrical signals in and rf resonator structure. We observe direct mixing of an applied optical sampling pulse with an ultrafast electrical signal capacitatively coupled to the sampling microbridge. The structures used here are 10 μm wide bridges lithographically defined in thin Tl2Ba2CaCu2O10 films. The time resolution and sensitivity of the technique are evaluated and the effects of bias currents on signal strengths are explored. © 2003 American Institute of Physics.
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06.60.Jn High-speed techniques (microsecond to femtosecond)
42.79.-e Optical elements, devices, and systems
74.78.-w Superconducting films and low-dimensional structures
85.25.-j Superconducting devices
74.72.-h Cuprate superconductors

Room-temperature low-voltage electroluminescence in amorphous carbon nitride thin films

R. Reyes, C. Legnani, P. M. Ribeiro Pinto, M. Cremona, P. J. G. de Araújo, and C. A. Achete

Appl. Phys. Lett. 82, 4017 (2003); http://dx.doi.org/10.1063/1.1581000 (3 pages) | Cited 17 times

Online Publication Date: 2 June 2003

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White-blue electroluminescent emission with a voltage bias less than 10 V was achieved in rf sputter-deposited amorphous carbon nitride (a-CN) and amorphous silicon carbon nitride (a-SiCN) thin-film-based devices. The heterojunction structures of these devices consist of: Indium tin oxide (ITO), used as a transparent anode; amorphous carbon film as an emission layer, and aluminum as a cathode. The thickness of the carbon films was about 250 Å. In all of the produced diodes, a stable visible emission peaked around 475 nm is observed at room temperature and the emission intensity increases with the current density. For an applied voltage of 14 V, the luminance was about 3 mCd/m2. The electroluminescent properties of the two devices are discussed and compared. © 2003 American Institute of Physics.
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78.66.Nk Insulators
78.60.Fi Electroluminescence
61.43.Er Other amorphous solids

Temperature transients and thermal properties of GaAs/AlGaAs quantum-cascade lasers

A. J. Borak, C. C. Phillips, and C. Sirtori

Appl. Phys. Lett. 82, 4020 (2003); http://dx.doi.org/10.1063/1.1582374 (3 pages) | Cited 9 times

Online Publication Date: 2 June 2003

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The use of a gated interband photoluminescence technique has allowed the study of the temperature transients in the active volume of a quantum-cascade laser during pulsed operation. The active region was found to rise by ∼40 K during a 150 ns current pulse, returning to the heat-sink temperature in ∼500 ns. The measured temperature transients were fitted, using a one-dimensional heat diffusion model, giving a value of kAR = 1.36±0.2 W cm−1 K−1 for the active region thermal conductivity, at 30 K. This is approximately ten times lower than literature values for bulk AlGaAs alloys of equivalent composition and has significant implications on the prospects for high-power continuous-wave device operation. © 2003 American Institute of Physics.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
78.55.Cr III-V semiconductors

Polymer laser fabricated by a simple micromolding process

Justin R. Lawrence, Graham A. Turnbull, and Ifor D. W. Samuel

Appl. Phys. Lett. 82, 4023 (2003); http://dx.doi.org/10.1063/1.1579858 (3 pages) | Cited 41 times

Online Publication Date: 2 June 2003

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We report polymer distributed feedback lasers fabricated using solvent-assisted microcontact molding. The poly[2-methoxy-5-(3,7-dimethyloctyloxy) paraphenylenevinylene] film is patterned by placing it in conformal contact with an elastomeric mould inked with a suitable solvent. When the resulting microstructured film is pumped with the 532 nm pulsed output of a microchip laser, we observe lasing above a threshold pump energy of 225 nJ. Above threshold the emission narrows to a linewidth of less than 0.6 nm at a wavelength of 638 nm. This micromolding technique may find application to a wide range of wavelength-scale microstructured organic photonic devices. © 2003 American Institute of Physics.
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42.70.Hj Laser materials
42.55.Px Semiconductor lasers; laser diodes
81.10.Fq Growth from melts; zone melting and refining
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.86.+b Optical workshop techniques
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
42.70.Jk Polymers and organics
42.60.By Design of specific laser systems

Electrically tunable waveguide laser based on ferroelectric liquid crystal

Masahiro Kasano, Masanori Ozaki, Katsumi Yoshino, Dirk Ganzke, and Wolfgang Haase

Appl. Phys. Lett. 82, 4026 (2003); http://dx.doi.org/10.1063/1.1580992 (3 pages) | Cited 18 times

Online Publication Date: 2 June 2003

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Laser action in a waveguide configuration has been demonstrated in a planar alignment cell of dye-doped chiral smectic liquid-crystal mixtures with a short pitch helical structure. In this configuration, doped dye can effectively be excited by a pump beam illuminating perpendicularly the helical axis and the laser light emitted along the helical axis propagates in the waveguide. Lasing wavelength can be tuned by adjusting the periodicity of the helical pitch upon applying the electric field. © 2003 American Institute of Physics.
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42.55.Mv Dye lasers
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
61.30.-v Liquid crystals

Monte Carlo simulation of tunable mid-infrared emission from coupled Wannier–Stark ladders in semiconductor superlattices

M. Manenti, F. Compagnone, A. Di Carlo, P. Lugli, G. Scamarcio, and F. Rizzi

Appl. Phys. Lett. 82, 4029 (2003); http://dx.doi.org/10.1063/1.1581382 (3 pages) | Cited 7 times

Online Publication Date: 2 June 2003

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We present a theoretical and experimental study on the mid-infrared electroluminescence associated with transitions between electric-field-induced conduction states, forming the Wannier–Stark ladder, in strongly coupled GaAs/AlAs superlattices. The interwell and intrawell radiative transitions in the whole range of electric fields from the moderate localization to the resonance-induced delocalization regimes have been experimentally investigated. Monte Carlo simulations show a very good agreement between experimental and theoretical electroluminescence spectra. Results show that the application of an electric field in the range from 100 to 250 kV/cm shifts the emission peak, related with interwell diagonal transitions between Stark-localized ground states of two adjacent wells, up to the limit corresponding to the merging of this electroluminescence peak with the intersubband emission between excited and ground state of the same well. The theoretical investigation indicates that interwell scattering via LO phonons is responsible for the population of the excited state of the ladder. © 2003 American Institute of Physics.
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78.60.Fi Electroluminescence
02.70.Uu Applications of Monte Carlo methods
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Photoluminescence enhancement of colloidal quantum dots embedded in a monolithic microcavity

Carl B. Poitras, Michal Lipson, Hui Du, Megan A. Hahn, and Todd D. Krauss

Appl. Phys. Lett. 82, 4032 (2003); http://dx.doi.org/10.1063/1.1581007 (3 pages) | Cited 28 times

Online Publication Date: 2 June 2003

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We demonstrate an enhancement of the spontaneous emission from colloidal CdSe quantum dots embedded in a half-wavelength one-dimensional cavity. When embedded in the cavity, the emission of the quantum dots is enhanced by a factor of 2.7. We also show a strong amplification by one order of magnitude in the absorption of the CdSe quantum dots due to the cavity effect. © 2003 American Institute of Physics.
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78.67.Hc Quantum dots
78.55.Et II-VI semiconductors

Enhanced room-temperature emission in Cr4+ ions containing alumino-silicate glasses

C. Batchelor, W. J. Chung, S. Shen, and A. Jha

Appl. Phys. Lett. 82, 4035 (2003); http://dx.doi.org/10.1063/1.1581374 (3 pages) | Cited 19 times

Online Publication Date: 2 June 2003

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The Bi2O3 modified alumino-silicate glasses, when excited at 800 nm exhibited a broadband emission of Cr4+ in the range of 1.2 to ∼1.6 μm at room temperature. The mean lifetime of (1E−3A2)→3T1 transition in Cr4+-doped glass at RT was as long as ∼426 μs, enabling the realization of both tunable lasers and broadband fiber amplifiers. The Cr4+ emission at RT also showed the dependency on the excitation wavelength and site distribution within the chosen glass host. A photoinduced charge transfer process from the Cr3+ ion into Cr4+ ion appears to be responsible for the excitation of Cr4+. © 2003 American Institute of Physics.
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78.55.Qr Amorphous materials; glasses and other disordered solids
42.55.Rz Doped-insulator lasers and other solid state lasers
42.70.Hj Laser materials
42.70.Ce Glasses, quartz

Extremely low threshold-current-density InGaAs quantum-well lasers with emission wavelength of 1215–1233 nm

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

Appl. Phys. Lett. 82, 4038 (2003); http://dx.doi.org/10.1063/1.1581978 (3 pages) | Cited 31 times

Online Publication Date: 2 June 2003

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Extremely low threshold-current-density In0.4Ga0.6As quantum-well (QW) lasers have been realized in the 1215–1233 nm wavelength regime. The measured room-temperature threshold current density of the InGaAs QW lasers with a cavity length of 1000 μm is only 90 A/cm2 at an emission wavelength of 1233 nm. © 2003 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
73.63.Hs Quantum wells
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Is Cu60Ti10Zr30 a bulk glass-forming alloy?

J. Z. Jiang, J. Saida, H. Kato, T. Ohsuna, and A. Inoue

Appl. Phys. Lett. 82, 4041 (2003); http://dx.doi.org/10.1063/1.1581001 (3 pages) | Cited 44 times

Online Publication Date: 2 June 2003

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The microstructures of Cu60Ti10Zr30 alloys fabricated by using two different methods, (rods of 2.5 mm in diameter prepared by a copper-mold casting method, and ribbons of about 0.03 mm in thickness prepared by the melt-spinning method), have been investigated by transmission electron microscopy and high-resolution transmission electron microscopy. Surprisingly, we found that the alloy in both geometries contains cubic nanometer-sized crystals of about 5–7 nm in diameter with a lattice parameter of 0.45 nm for ribbons and 7–15 nm in diameter with a lattice parameter of 0.42 nm for rods. Nanocrystals with a significant volume fraction are randomly distributed in the amorphous matrix. The copper element is enriched in nanocrystals while a slightly high zirconium content is found in the matrix. We classify that the Cu60Ti10Zr30 alloy prepared by both of the aforementioned methods is a nanocomposite: Nanocrystals embedded in an amorphous matrix. © 2003 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
81.20.-n Methods of materials synthesis and materials processing

Structures of nitrided Si(001) surfaces: First-principles theoretical study

Shin’ichi Higai and Takahisa Ohno

Appl. Phys. Lett. 82, 4044 (2003); http://dx.doi.org/10.1063/1.1580639 (3 pages) | Cited 2 times

Online Publication Date: 2 June 2003

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First-principles theoretical calculations for nitrided Si(001) surfaces are presented. We examined the structure and stability of ordered nitrided surfaces with various coverages of N and H atoms. For the 2×2 ordered reconstruction observed in very recent experiments, we propose a structural model, where N atoms are adsorbed into Si dimer centers and also into back bonds, and those in the dimer centers are dimerized. We also discuss the nitridation process. © 2003 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.43.Fg Adsorbate structure (binding sites, geometry)
81.65.Lp Surface hardening: nitridation, carburization, carbonitridation

Parameters of wires during electric explosion

S. I. Tkachenko, V. S. Vorob’ev, and S. P. Malyshenko

Appl. Phys. Lett. 82, 4047 (2003); http://dx.doi.org/10.1063/1.1580996 (3 pages) | Cited 10 times

Online Publication Date: 2 June 2003

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We use the nucleation theory of electric explosion of wire to estimate wire parameters at the explosion for a wide range of experimental conditions. We analyze a number of the major parameters including the limit value of energy deposited during the initial resistive phase of the explosion and discuss the correspondence of these results to previously published experimental data. © 2003 American Institute of Physics.
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52.80.Qj Explosions; exploding wires

Orientation control of poly(vinylidenefluoride-trifluoroethylene) crystals and molecules using atomic force microscopy

Kuniko Kimura, Kei Kobayashi, Hirofumi Yamada, Toshihisa Horiuchi, Kenji Ishida, and Kazumi Matsushige

Appl. Phys. Lett. 82, 4050 (2003); http://dx.doi.org/10.1063/1.1581974 (3 pages) | Cited 21 times

Online Publication Date: 2 June 2003

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We have developed an aligning technique for polymer crystals and molecular chains utilizing contact-mode atomic force microscopy (AFM). We have aligned lamellar crystals and molecular chains of poly(vinylidenefluoride-trifluoroethylene) thin films. By scanning the film surface using an AFM cantilever tip at the temperature range of 70–100 °C, we aligned the crystals to the scan direction. Moreover, we successfully aligned the molecular chains to the scan direction by scanning at a higher temperature (135 °C). The aligned chains subsequently formed large lamellar crystals, which were still ferroelectric. © 2003 American Institute of Physics.
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61.41.+e Polymers, elastomers, and plastics
68.55.-a Thin film structure and morphology
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
68.37.Ps Atomic force microscopy (AFM)
36.20.-r Macromolecules and polymer molecules
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Jd Polymers; organic compounds
77.55.-g Dielectric thin films
07.79.Lh Atomic force microscopes

Oxygen vacancy ordering in epitaxial layers of yttrium oxide on Si (001)

A. Travlos, N. Boukos, G. Apostolopoulos, and A. Dimoulas

Appl. Phys. Lett. 82, 4053 (2003); http://dx.doi.org/10.1063/1.1581985 (3 pages) | Cited 19 times

Online Publication Date: 2 June 2003

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The origin of the superstructure observed in epitaxial yttrium oxide (Y2O3) layers on Si (001) is determined by electron energy loss spectroscopy (EELS). The oxygen K edge is measured both in the superstructure and a defect-free region of the Y2O3 layers and they are compared to EELS spectra obtained from bulk stoichiometric and reduced Y2O3. It is shown that as a result of the epitaxial growth, oxygen vacancies order into a superstructure creating nonstoichiometric regions in an otherwise stoichiometric Y2O3 layer. Furthermore, it is shown that oxygen deficiency introduces a change of the density of states of the lower conduction band of Y2O3. © 2003 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.J- Point defects and defect clusters
61.66.Bi Elemental solids
61.66.Dk Alloys
79.20.Uv Electron energy loss spectroscopy

Photoluminescence of a superficial Si nanolayer and an example of its use

M. Ley, V. Svrcek, and Z. T. Kuznicki

Appl. Phys. Lett. 82, 4056 (2003); http://dx.doi.org/10.1063/1.1581984 (3 pages) | Cited 3 times

Online Publication Date: 2 June 2003

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A characteristic photoluminescence of a superficial Si nanolayer realized by ion implantation has been observed. This effect, being totally independent of those shown recently for a nanoscale Si-layered system, is similar to that produced by Si nanocrystals (Si nc). To visualize the nature and give evidence of this effect, we fabricated samples in two different ways: (i) by incorporation of Si nc into thin SiO2 films deposited on Si wafer by the spin-on-glass method and (ii) by a nanoscale superficial crystalline-Si modification using medium-energy ion implantation and thermal treatment. In both cases the UV-to-red light conversion has been observed to be independent of wafer post-implantation damage. To show the UV-to-red conversion contribution, we use the ion modified superficial Si layer with its well-defined potential barrier, the so-called carrier collection limit. Such a modified Si structure gives us a method of deconvoluting several optoelectronic features observed experimentally on modified Si. The practical realization is compatible with well-established Si technology. © 2003 American Institute of Physics.
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78.55.Ap Elemental semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.05.Cy Elemental semiconductors
81.07.Bc Nanocrystalline materials
71.20.Mq Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
61.46.-w Structure of nanoscale materials
61.72.up Other materials
61.80.Jh Ion radiation effects
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
85.40.Ry Impurity doping, diffusion and ion implantation technology

Optical phonon spectra of GaP nanoparticles prepared by nanochemistry

F. S. Manciu, Y. Sahoo, D. J. MacRae, M. Furis, B. D. McCombe, and P. N. Prasad

Appl. Phys. Lett. 82, 4059 (2003); http://dx.doi.org/10.1063/1.1580635 (3 pages) | Cited 3 times

Online Publication Date: 2 June 2003

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Gallium phosphide (GaP) nanoparticles have been synthesized by colloidal nanochemistry with two different surfactants: trioctylphosphine oxide and dodecylamine. Transverse optical (bulk) and surface optical phonons associated with the GaP nanoparticles were observed and studied experimentally by infrared transmission spectroscopy of a solid dispersion of these nanoparticles in cesium iodide pellets. These vibrational properties of the nanoparticles were used to obtain information about the crystallinity and surface interactions. The crystallinity and the stoichiometry of the samples were also examined and characterized by transmission electron microscopy, electron diffraction, and energy dispersive x-ray spectroscopy. © 2003 American Institute of Physics.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.30.Hv Other nonmetallic inorganics
81.07.Bc Nanocrystalline materials
68.37.Lp Transmission electron microscopy (TEM)

Periodical poling characteristics of congruent MgO:LiNbO3 crystals at elevated temperature

Hideki Ishizuki, Ichiro Shoji, and Takunori Taira

Appl. Phys. Lett. 82, 4062 (2003); http://dx.doi.org/10.1063/1.1582371 (3 pages) | Cited 32 times

Online Publication Date: 2 June 2003

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A structure for quasi-phase matching of large cross section using 5 mol % MgO-doped LiNbO3 (MgO:LN) crystal for high-power wavelength conversion was realized. We have found that the coercive field to invert polarization of the crystal reduces drastically with elevated temperature. The coercive field reduces to 1.2 kV/mm at 250 °C, which is about 1/4 compared with that for MgO:LN at room temperature (RT) and about 1/17 of that for LN at RT. 3 mm thick periodically poled MgO:LN has been fabricated with 30 μm period. © 2003 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
77.22.Ej Polarization and depolarization
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Midinfrared continuous-wave photoluminescence of lead–salt structures up to temperatures of 190 °C

M. Böberl, W. Heiss, T. Schwarzl, K. Wiesauer, and G. Springholz

Appl. Phys. Lett. 82, 4065 (2003); http://dx.doi.org/10.1063/1.1582370 (3 pages) | Cited 21 times

Online Publication Date: 2 June 2003

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Continuous-wave photoluminescence in the midinfrared for PbSe/PbEuSe and PbTe/PbEuTe multiquantum well structures as well as for PbSe and PbTe bulklike structures, excited by a semiconductor laser diode, is investigated. All samples are grown by molecular-beam epitaxy on BaF2(111) substrates under the same growth conditions. Both for the Te-based systems and for the Se-based systems, it turns out that bulklike structures show photoluminescence up to higher temperatures than multiquantum well structures. In particular, emission spectra from PbTe/PbEuTe multiquantum wells are obtained up to temperatures of 200 K and from PbSe/PbEuSe multiquantum well structures up to 60 °C whereas for bulklike PbSe photoluminescence at temperatures as high as 190 °C is demonstrated. © 2003 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
78.67.De Quantum wells
78.66.Li Other semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Experimental evidence of polarization dependence in the optical response of opal-based photonic crystals

J. F. Galisteo-Lopez, F. López-Tejeira, S. Rubio, C. López, and J. Sánchez-Dehesa

Appl. Phys. Lett. 82, 4068 (2003); http://dx.doi.org/10.1063/1.1582379 (3 pages) | Cited 30 times

Online Publication Date: 2 June 2003

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We report angle resolved reflectivity measurements showing the polarization dependence of the pseudogap in artificial opals. This kind of photonic crystals consist of silica spheres ordered in a face-centered-cubic lattice. The analyzed gap originates from the (111) family of planes. It is shown that the width of the Bragg peak observed in the reflectance spectra follows the bands determining the pseudogap, which are selectively excited according to the polarization (s or p) of the light impinging on the opal. Moreover, it is found that the coupling of light with the photonic bands occurs according to their predicted symmetry, which was assigned by arguments based on group theory. © 2003 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
42.25.Ja Polarization
78.20.-e Optical properties of bulk materials and thin films

High-resolution near-field spectroscopy investigation of GaN laterally overgrown structures on SiC

F. Hitzel, A. Hangleiter, S. Miller, A. Weimar, G. Brüderl, A. Lell, and V. Härle

Appl. Phys. Lett. 82, 4071 (2003); http://dx.doi.org/10.1063/1.1580997 (3 pages)

Online Publication Date: 2 June 2003

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We investigated epitaxial lateral overgrown GaN structures with different wing tilt using a spectroscopic scanning near-field optical microscope (spectroscopic SNOM), which takes a complete optical spectrum at each point of a sample surface. From these measurements, we obtain information about strain at different points of the surface, and comparing emission intensity between regions of lateral growth and vertical growth, we directly see the efficiency of defect density reduction. For the high wing-tilt sample, an increased defect density at the window–wing interface could be identified. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.37.Uv Near-field scanning microscopy and spectroscopy
68.60.Bs Mechanical and acoustical properties
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Si dangling-bond-type defects at the interface of (100)Si with ultrathin HfO2

A. Stesmans and V. V. Afanas’ev

Appl. Phys. Lett. 82, 4074 (2003); http://dx.doi.org/10.1063/1.1579564 (3 pages) | Cited 45 times

Online Publication Date: 2 June 2003

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Electron spin resonance analysis of (100)Si/HfO2 interfaces prepared by chemical vapor deposition of the oxide using three chemically different precursors reveals that the trivalent Si defects common for Si/SiO2 interfaces—Pb0 and Pb1 centers—are universally observed upon hydrogen detachment. The density of the Pb0 is higher than in the (100)Si/SiO2 structures and is sensitive to the deposition process. However, the density can be significantly reduced by annealing of the Si/HfO2 structures in O-containing ambient, likely through re-establishing the Si/SiO2 interface. Also, the Pb-type centers can be entirely passivated by hydrogen already at 400 °C. The density of fast interface states closely follows the variations in the Pb0 center density, suggesting it as the dominant contribution to the fast interface states. © 2003 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
76.30.Mi Color centers and other defects
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.Cc Kinetics of defect formation and annealing

Temperature dependence of carrier mobility in Si wafers measured by infrared photocarrier radiometry

Jerias Batista, Andreas Mandelis, and Derrick Shaughnessy

Appl. Phys. Lett. 82, 4077 (2003); http://dx.doi.org/10.1063/1.1582376 (3 pages) | Cited 29 times

Online Publication Date: 2 June 2003

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A recently introduced infrared photocarrier radiometry technique has been used to determine the temperature dependence of carrier mobility in Si wafers. In addition, its potential to determine simultaneously the carrier lifetime, diffusion coefficient, and surface recombination velocity is reported. This noncontact, nonintrusive, and all-optical technique relies on the detection of infrared radiation from harmonically excited free carriers (pure electronic diffusion-wave detection). Using a multiparameter fitting to a complete theory, the results showed that the lifetime increases with temperature, the diffusion coefficient decreases [D(T) ∼ T−1.5], and the temperature dependence of carrier mobility is μ(T) = (1.06±0.07)×109×T−2.49±0.01 cm2/V s. © 2003 American Institute of Physics.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Cw Elemental semiconductors
73.25.+i Surface conductivity and carrier phenomena
72.40.+w Photoconduction and photovoltaic effects
72.20.Fr Low-field transport and mobility; piezoresistance
07.60.Dq Photometers, radiometers, and colorimeters

Stimulated emission and ultrafast carrier relaxation in AlGaN/GaN multiple quantum wells

Ümit Özgür, Henry O. Everitt, Lei He, and Hadis Morkoç

Appl. Phys. Lett. 82, 4080 (2003); http://dx.doi.org/10.1063/1.1581385 (3 pages) | Cited 9 times

Online Publication Date: 2 June 2003

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Stimulated emission (SE) and ultrafast carrier relaxation dynamics were measured in two AlxGa1−xN/GaN multiple-quantum-well (MQW) structures, grown in a Ga-rich environment with x = 0.2 and 0.3, respectively. The threshold density for SE (Ith ≃ 100 μJ/cm2) was found to be independent of x. Room-temperature, time-resolved, differential transmission measurements mapped the carrier relaxation mechanisms for above barrier energy excitation. Photoexcited carriers are observed to relax into the QWs in <1 ps, while carrier recombination times as fast as 30 ps were measured. For excitation above Ith, SE is shown to deplete carriers in the barriers through a cascaded refilling of the QW state undergoing SE. Similar behavior is seen in an Al0.3Ga0.7N/GaN MQW grown with a N-rich atmosphere, but the relaxation phenomena of all AlGaN MQWs are significantly faster than observed in InGaN MQWs of similar structure. © 2003 American Institute of Physics.
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78.45.+h Stimulated emission
78.47.-p Spectroscopy of solid state dynamics
73.63.Hs Quantum wells
78.67.De Quantum wells
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Deep-defect-induced quenching effects in semi-insulating GaN layers detected by photoelectrical spectroscopic techniques

H. Witte, A. Krtschil, M. Lisker, E. Schrenk, J. Christen, A. Krost, B. Kuhn, and F. Scholz

Appl. Phys. Lett. 82, 4083 (2003); http://dx.doi.org/10.1063/1.1579556 (3 pages) | Cited 6 times

Online Publication Date: 2 June 2003

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Quenching effects induced by additional below-bandgap illumination in undoped semi-insulating GaN were investigated using optical admittance spectroscopy (OAS) and photocurrent (PC) spectroscopy as well as optically excited, thermally stimulated currents (TSC). In OAS and PC, a decrease of defect-related signals due to the quenching light was observed. The thermal quenching of the defect band between 2.7 and 3.3 eV shows a good agreement with thermal emissions as measured by TSC, indicating the same defects cause the optical transitions in OAS/PC and the thermal transitions in TSC. The thermal emission in the temperature region between 250 and 300 K, which is responsible for the thermal quenching of the blue band (BB) in OAS, also shows an optical quenching under below-bandgap excitation. © 2003 American Institute of Physics.
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72.40.+w Photoconduction and photovoltaic effects
77.22.Ej Polarization and depolarization
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.55.Cr III-V semiconductors
71.55.Eq III-V semiconductors
72.80.Ey III-V and II-VI semiconductors
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