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4 Oct 1999

Volume 75, Issue 14, pp. 1999-2151

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Comparison of the quantum efficiencies of interwell and intrawell radiative transitions in quantum cascade lasers

K. Donovan, P. Harrison, and R. W. Kelsall

Appl. Phys. Lett. 75, 1999 (1999); http://dx.doi.org/10.1063/1.124895 (3 pages) | Cited 12 times

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A theoretical study has been made to compare the quantum efficiencies of interwell and intrawell radiative transitions in quantum cascade lasers based on AlxGa1−xAs/GaAs technology. Radiative and nonradiative intersubband transition rates were calculated for a range of temperatures between 4 and 300 K at an applied electric field of 4 kV cm−1 for structures designed to emit in both mid-infrared and far-infrared frequency ranges. It is found that the internal quantum efficiency of mid-infrared devices is a maximum for diagonal, or interwell, transitions. Conversely, for the far-infrared devices, the quantum efficiency is a maximum for vertical, or intrawell, transitions. © 1999 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
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

High-power, reliable operation of 730 nm AlGaAs laser diodes

R. Singh, D. Bull, F. P. Dabkowski, E. Clausen, and A. K. Chin

Appl. Phys. Lett. 75, 2002 (1999); http://dx.doi.org/10.1063/1.124896 (3 pages) | Cited 7 times

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High-power operation of AlGaAs multi-quantum-well laser diodes emitting near 730 nm is reported. 1000 h, reliable operation at a power of 1.0 W for 100 μm emission aperture and 500 μm cavity length devices has been demonstrated at room temperature. These devices have threshold current densities of 770 A/cm2 with the characteristic temperature coefficients of threshold current, T0, and external differential quantum efficiency, T1, of 152 and 167 K, respectively. © 1999 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
78.66.Fd III-V semiconductors

Er doped nanocrystalline ZnO planar waveguide structures for 1.55 μm amplifier applications

N. Mais, J. P. Reithmaier, A. Forchel, M. Kohls, L. Spanhel, and G. Müller

Appl. Phys. Lett. 75, 2005 (1999); http://dx.doi.org/10.1063/1.124897 (3 pages) | Cited 39 times

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Amplifying planar waveguide structures in Er-doped nanocrystalline II/VI semiconductor layer systems were developed by photolithography and wet chemical etching. 2 μm thick planar waveguides on glass substrates with lateral dimensions down to 5 μm with rectangular cross section were realized. By optical excitation a maximum gain of 82 cm−1 could be determined, which is sufficiently high to allow the design of compact planar amplifiers in this material system. The influence of a thermal sintering step on the gain spectrum and on the fluorescence lifetime has been investigated. By increasing the sintering temperature to 800 °C a consistent increase of gain and fluorescence lifetime was observed. © 1999 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.79.Gn Optical waveguides and couplers
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors
81.65.Cf Surface cleaning, etching, patterning
42.86.+b Optical workshop techniques

Standing wave detection and interferometer application using a photodiode thinner than optical wavelength

Minoru Sasaki, Xiaoyu Mi, and Kazuhiro Hane

Appl. Phys. Lett. 75, 2008 (1999); http://dx.doi.org/10.1063/1.124898 (3 pages) | Cited 15 times

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A thin film photodiode whose active layer is thinner than the wavelength of the incident light is described. A part of the incident photon is detected and the rest transmits through the thin film photodiode without absorption. Being inserted in the optical field, this sensor is applied to construct the new interferometer detecting the intensity profile of the standing wave of the thinnest interference fringe. © 1999 American Institute of Physics.
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07.60.Ly Interferometers
85.60.Dw Photodiodes; phototransistors; photoresistors
85.60.Gz Photodetectors (including infrared and CCD detectors)

Evidence of energy coupling between Si nanocrystals and Er3+ in ion-implanted silica thin films

C. E. Chryssou, A. J. Kenyon, T. S. Iwayama, C. W. Pitt, and D. E. Hole

Appl. Phys. Lett. 75, 2011 (1999); http://dx.doi.org/10.1063/1.124899 (3 pages) | Cited 73 times

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Silica thin films containing Si nanocrystals and Er3+ were prepared by ion implantation. Excess Si concentrations ranged from 5% to 15%; Er3+ concentration for all samples was 0.5%. Samples exhibited photoluminescence at 742 nm (attributed to Si nanocrystals), 654 nm (defects due to Er3+ implantation), and at 1.53 μm (intra-4f transitions). Photoluminescence intensity at 1.53 μm increased ten times by incorporating Si nanocrystals. Strong, broad photoluminescence at 1.53 μm was observed for λPump away from Er3+ absorption peaks, implying energy transfer from Si nanocrystals. Erbium fluorescence lifetime decreased from 4 ms to 1 ms when excess Si increased from 5% to 15%, suggesting that at high Si content Er3+ ions are primarily situated inside Si nanocrystals. © 1999 American Institute of Physics.
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78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
73.22.-f Electronic structure of nanoscale materials and related systems
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
61.46.-w Structure of nanoscale materials
78.66.Nk Insulators

Ionochromism in a light-emitting electrochemical cell with low response time based on an ionic conductive poly-phenylene vinylene

L. Holzer, F. P. Wenzl, S. Tasch, G. Leising, B. Winkler, L. Dai, and A. W. H. Mau

Appl. Phys. Lett. 75, 2014 (1999); http://dx.doi.org/10.1063/1.124900 (3 pages) | Cited 15 times

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Characterizations of red-orange light-emitting electrochemical cells (LECs) based on poly[1,4-(2,5-bis(1,4,7,10-tetraoxaundecyl))phenylene vinylene], (BTEM-PPV), are presented, BTEM-PPV combines good electronic conductivity with ionic conductivity due to its conjugated backbone and side chains consisting of oligo(ethylene oxide). The use of this polymer in LECs leads to relatively bright light emitting devices with low response times which are obtained without blending an additional ionic conductive polymer into the film. The response times of the BTEM-LECs driven with a square wave form pulse were determined to be about 480 μs. The value for the turn-on voltage of the electroluminescence is 2 V and at 3 V a brightness of around 35 cd/m2 was obtained. BTEM-PPV complexed with metal ions shows an ionochromic effect in the absorption spectrum and also in the electroluminescence spectrum due to the covalent linkage of the glymelike side chains to the PPV backbone, which represents an approach toward chemical sensors. © 1999 American Institute of Physics.
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42.70.Jk Polymers and organics
72.15.Nj Collective modes (e.g., in one-dimensional conductors)
66.30.H- Self-diffusion and ionic conduction in nonmetals
78.60.Fi Electroluminescence
85.60.Jb Light-emitting devices
82.47.-a Applied electrochemistry

Space–time digital holography: A three-dimensional microscopic imaging scheme with an arbitrary degree of spatial coherence

Guy Indebetouw and Prapong Klysubun

Appl. Phys. Lett. 75, 2017 (1999); http://dx.doi.org/10.1063/1.124901 (3 pages) | Cited 14 times

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An on-line, spatiotemporal, digital holographic method is described and demonstrated experimentally. Using interferometric imaging, each scatterer of a three-dimensional object is encoded as a temporally modulated Fresnel pattern, and recorded on a charge-coupled device. Temporal heterodyning of the signal from each pixel results in a single-sideband, on-line holographic record in digital form. Reconstruction of an image focused on a chosen transverse plane in the object is done by digital correlation with a reconstruction function matched to that plane. The method circumvents most of the drawbacks of both coherent and incoherent holography, and may find applications in three-dimensional imaging and microscopy. © 1999 American Institute of Physics.
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42.40.Kw Holographic interferometry; other holographic techniques
07.60.Ly Interferometers
42.30.Wb Image reconstruction; tomography
07.60.Pb Conventional optical microscopes

Ideal performance of cascade and noncascade intersubband and interband long-wavelength semiconductor lasers

Michael E. Flatté, J. T. Olesberg, and C. H. Grein

Appl. Phys. Lett. 75, 2020 (1999); http://dx.doi.org/10.1063/1.124902 (3 pages)

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The ideal performance of cascade and noncascade intersubband and interband laser active regions is directly compared in a cavity-insensitive way. For devices not limited by series resistance or series voltage (such as can in principle be accomplished by cascading) the relevant figure of merit is the net material gain per unit volumetric power dissipation density in the active region. This figure of merit is evaluated at 77 and 300 K for a variety of structures relying on interband and intersubband transitions, each of which may constitute the active region of a cascade or noncascade device. A design for an 11 μm laser active region is proposed whose ideal performance exceeds that of current intersubband lasers. © 1999 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
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Attachment-induced ionization instability of a radio frequency excited discharge in oxygen

H.-M. Katsch, A. Goehlich, T. Kawetzki, E. Quandt, and H.-F. Döbele

Appl. Phys. Lett. 75, 2023 (1999); http://dx.doi.org/10.1063/1.124903 (3 pages) | Cited 10 times

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The plasma of a 13.56 MHz capacitively coupled oxygen discharge of the Gaseous Electronics Conference Reference Cell type exhibits fluctuations of the plasma potential and of light emission in the kilohertz range. This behavior can be explained in terms of an attachment-induced ionization instability in connection with a sufficiently high fraction of negative ions. A necessary condition for the appearance of this type of instability is a strong positive dependence on electron temperature of the electron attachment coefficient describing the formation of negative oxygen ions. A strong volume loss of negative ions by neutral particles—metastable molecules in the present case—is an additional condition. Calculations of the temperature dependent coefficients for ionization and attachment by solving the time-independent Boltzmann equation in the two-term approximation in combination with the fluid equations of the charge carriers show that the criteria for the development of an attachment-induced ionization instability are fulfilled in the pressure domain around 30 Pa and for medium radio frequency voltages around 300 V. © 1999 American Institute of Physics.
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52.80.-s Electric discharges
34.50.Gb Electronic excitation and ionization of molecules
51.50.+v Electrical properties (ionization, breakdown, electron and ion mobility, etc.)
52.25.-b Plasma properties

Soft x-ray emissions from laser plasma of cryogenic mixture targets

Atsushi Shimoura, Takayasu Mochizuki, Shuji Miyamoto, Sho Amano, and Tadao Uyama

Appl. Phys. Lett. 75, 2026 (1999); http://dx.doi.org/10.1063/1.124904 (3 pages) | Cited 15 times

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Soft x-ray spectral radiation from Xe–CO2 mixture cryogenic targets with a Xe mole fraction of 0% (pure CO2) to 100% (pure Xe) irradiated by a 1 μm pulse laser at a laser intensity IL of 0.3–1.0×1012 W/cm2 has been observed. The x-ray conversion efficiency per Xe mole fraction was found to have maximum values at the Xe fractions of 10% for IL = 6.0×1011 W/cm2 and 5% for IL = 1.2×1012 W/cm2, which were about five and ten times as large as that in a pure Xe target, respectively. The x-ray conversion efficiencies in the cryogenic mixture targets at Xe fractions of 10%–40% were about 1.3 %/sr/nm for λ = 10.8 nm and IL = 1012 W/cm2, which was as high as that in a pure Xe cryogenic target. The physical mechanism behind this enhanced emission is discussed. © 1999 American Institute of Physics.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
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Violet and blue emitting (In,Ga)N/GaN multiple quantum wells grown on γ-LiAlO2(100) by radio frequency plasma-assisted molecular beam epitaxy

P. Waltereit, O. Brandt, and K. H. Ploog

Appl. Phys. Lett. 75, 2029 (1999); http://dx.doi.org/10.1063/1.124905 (3 pages) | Cited 10 times

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We study the growth of GaN and (In,Ga)N/GaN multiple quantum wells on γ-LiAlO2 by rf plasma-assisted molecular beam epitaxy. The GaN layers exhibit promising optical and electrical properties, whereas the structural quality is significantly influenced by inferior substrate morphology. The (In,Ga)N/GaN multiple quantum well structures show intense room-temperature photoluminescence in the violet and blue spectral range. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.55.Cr III-V semiconductors
73.61.Ey III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors

The effects of x-ray induced structural changes on the microstructure of a-Si after thermal crystallization

Kin Man Yu, Wladyslaw Walukiewicz, Shunsuke Muto, Hyun-Chul Jin, and John R. Abelson

Appl. Phys. Lett. 75, 2032 (1999); http://dx.doi.org/10.1063/1.124906 (3 pages) | Cited 5 times

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We have investigated the effects of intense x-ray irradiation on the local relaxation in amorphous silicon films doped with Ge(a-Si:Ge) and subsequently the crystallization behavior of these films. The Ge–Si bond distance in the as-grown a-Si:Ge is slightly longer (∼0.004 Å) than for the crystalline case (2.378 Å). When the a-Si:Ge film was exposed to synchrotron x rays, the Ge–Si bond distance increased to a value closer to the sum of the covalent radii of Si and Ge (2.39 Å). This x-ray-induced bond length dilation is found to be x-ray dose dependent and is strongest in the sample irradiated with x rays for 20 h (corresponding to a dose of ∼1 photon/Si atom). The x-ray-induced bond dilation in the a-Si:Ge directly affects the crystallization of the films after irradiation. We found that the final grain size of the annealed Si crystal depends on the initial Ge–Si bond length in the amorphous film. The larger the RGe–Si (due to x-ray irradiation) the larger is the Si grain size after thermal annealing. The mechanism leading to the lattice relaxation in the amorphous phase and subsequently the crystal grain size after annealing due to x-ray irradiation will be discussed. © 1999 American Institute of Physics.
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61.43.Dq Amorphous semiconductors, metals, and alloys
61.80.Cb X-ray effects
61.82.Fk Semiconductors

Electrode versus space-charge-limited conduction in organic light-emitting diodes

U. Wolf, S. Barth, and H. Bässler

Appl. Phys. Lett. 75, 2035 (1999); http://dx.doi.org/10.1063/1.124907 (3 pages) | Cited 24 times

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A criterion is established to distinguish electrode limited charge injection from a metal into a random organic dielectric from space charge limited current flow. The crucial material parameters are the charge carrier mobility and the zero field injection barrier. It rests upon parametrizing the injection current as a function of electric field, temperature, and injection barrier by mutual adjustment of the electron current injected across a Mg:Ag∣Alq3 electrode on the one hand and Monte Carlo simulation of the injection yield for a hopping system on the other hand. © 1999 American Institute of Physics.
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85.60.Jb Light-emitting devices
73.61.Ph Polymers; organic compounds
73.50.Fq High-field and nonlinear effects
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Temperature dependence of photoluminescence on molecular-beam-epitaxy grown Ga2O3(Gd2O3)/GaAs

L. W. Tu, Y. C. Lee, K. H. Lee, C. M. Lai, I. Lo, K. Y. Hsieh, and M. Hong

Appl. Phys. Lett. 75, 2038 (1999); http://dx.doi.org/10.1063/1.124908 (3 pages) | Cited 6 times

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Device-quality Ga2O3(Gd2O3) thin films have been grown on GaAs using molecular-beam epitaxy. Photoluminescence measurements have been performed within a temperature range of 4.2–300 K. Detailed analysis on the peak position, peak width, and peak intensity has been compared with those of a conventional Al0.45Ga0.55As/GaAs sample, which is known to be the state-of-the-art structure of dielectrics/GaAs. Both the peak intensity and the peak width are very similar between the two. The results show an almost indistinguishable excellent quality between the Ga2O3(Gd2O3)/GaAs and the Al0.45Ga0.55As/GaAs samples. This demonstrates the superiority of the Ga2O3(Gd2O3)/GaAs structure and supports further the reported successfully manufactured GaAs metal-oxide-semiconductor field-effect transistors using this Ga2O3(Gd2O3) as the gate oxide. © 1999 American Institute of Physics.
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78.66.Nk Insulators
78.55.Hx Other solid inorganic materials
71.35.-y Excitons and related phenomena

Room-temperature photoluminescence excitation spectroscopy of Er3+ ions in Er- and (Er+Yb)-doped SiO2 films

A. Kozanecki, H. Przybylinska, W. Jantsch, and L. Palmetshofer

Appl. Phys. Lett. 75, 2041 (1999); http://dx.doi.org/10.1063/1.124909 (3 pages) | Cited 1 time

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We apply photoluminescence excitation spectroscopy to study the efficiency of excitation at 960–990 nm of the 1.54 μm emission of erbium implanted into SiO2 films thermally grown on silicon for a range of Er and Yb concentrations. We show that, in silica films doped solely with Er, the concentration of Er should be lower than 1020 cm−3 to prevent efficient concentration quenching of the emission. It is shown that the Yb/Er concentration ratio of 1–2 is optimum for the dopant densities of 1–2×1020 cm−3, whereas 1021 cm−3 results in quenching of the emission due to energy losses within the Yb subsystem. © 1999 American Institute of Physics.
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78.66.Nk Insulators
78.55.Hx Other solid inorganic materials

Multiwalled carbon nanotubes growth in anodic alumina nanoholes

Tatsuya Iwasaki, Taiko Motoi, and Tohru Den

Appl. Phys. Lett. 75, 2044 (1999); http://dx.doi.org/10.1063/1.124910 (3 pages) | Cited 78 times

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Carbon nanotubes (CNTs), standing perpendicularly to a substrate with an electrode, were fabricated by thermal catalytic decomposition of ethylene from Co particles electrochemically embedded at the bottom of anodic alumina nanoholes. The thermal durability of the alumina nanoholes for the CNTs growth process was achieved by using Nb as an underlying electrode. The CNTs were electrically connected to the electrode through the conductive paths, which were formed at the bottom of alumina nanoholes by Nb ion migration from the underlying electrode during anodization. © 1999 American Institute of Physics.
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81.05.ub Fullerenes and related materials
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Highly ordered two-dimensional carbon nanotube arrays

Jung Sang Suh and Jin Seung Lee

Appl. Phys. Lett. 75, 2047 (1999); http://dx.doi.org/10.1063/1.124911 (3 pages) | Cited 110 times

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Highly ordered multiwalled carbon nanotube arrays have been fabricated by using porous anodic alumina templates prepared by a two-step anodization process. Nanotubes were very uniform in diameter. Two-dimensional tube arrays were highly ordered within domain boundaries, and their vertical alignment was nearly perfect. The density of nanotubes, 1.1×1010 tubes/cm2, was very high. Our fabrication technique enabled us to easily control the tube diameter, length, and density. There was no practical limitation to the size of the alumina template, so that very large panels of well-aligned carbon nanotubes could be made. Our results offer a potentially elegant technique for fabricating cold-cathode flat panel displays. © 1999 American Institute of Physics.
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81.05.ub Fullerenes and related materials
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
85.65.+h Molecular electronic devices
07.07.Hj Display and recording equipment, oscilloscopes, TV cameras, etc.

Contrast enhancement of rare-earth switchable mirrors through microscopic shutter effect

D. G. Nagengast, A. T. M. van Gogh, E. S. Kooij, B. Dam, and R. Griessen

Appl. Phys. Lett. 75, 2050 (1999); http://dx.doi.org/10.1063/1.124912 (3 pages) | Cited 31 times

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In contrast to the binary switchable mirror films (YHx, LaHx, REHx with RE:rare earth) which have a weak red transparency window in their metallic dihydride phase, rare-earth alloys containing magnesium are remarkable for the large contrast between their metallic dihydride and transparent trihydride phase. By means of structural, optical transmittance, and electrical resistivity measurements on a series of Y1−yMgyHx, films we show that this is due to a disproportionation of the alloy. While the yttrium dihydride phase is formed, Mg separates out, remaining in its metallic state. Upon further loading, insulating MgH2 is formed together with cubic YH3−δ. In this way Mg acts essentially as a microscopic optical shutter, enhancing the reflectivity of these switchable mirrors in the metallic state and increasing the optical gap in the transparent state. © 1999 American Institute of Physics.
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42.79.Bh Lenses, prisms and mirrors
42.79.Wc Optical coatings
78.66.Nk Insulators

Strong reduction of interchain interaction by bridged chain substitution in luminescent phenylenevinylene thin films

Luca Chiavarone, Marco Di Terlizzi, Gaetano Scamarcio, Francesco Babudri, Gianluca M. Farinola, and Francesco Naso

Appl. Phys. Lett. 75, 2053 (1999); http://dx.doi.org/10.1063/1.124913 (3 pages) | Cited 9 times

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The strong reduction of interchain interaction in poly-(2,5-dialkoxy-1,4-phenylenevinylene) films with a 2,5 O–(CH2)12–O closed chain substitution (bridged PPV), engineered to reduce the molecular packing in the solid state, is reported. Evidence of this effect unambiguously stems from the systematic comparison between the optical properties of a series of dialkoxy-PPV derivatives with bridged and open chain side groups. Reduction of interchain energy relaxation channels explains the close similarity between the optical spectra of bridged-PPV films and solutions, the higher photoluminescence efficiency and the lower threshold for the observation of spectral line narrowing in the solid state. © 1999 American Institute of Physics.
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61.41.+e Polymers, elastomers, and plastics
68.55.-a Thin film structure and morphology
78.66.Qn Polymers; organic compounds
42.70.Jk Polymers and organics
78.55.Kz Solid organic materials

Molecular dynamics simulation of thermal conductivity of silicon nanowires

Sebastian G. Volz and Gang Chen

Appl. Phys. Lett. 75, 2056 (1999); http://dx.doi.org/10.1063/1.124914 (3 pages) | Cited 109 times

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We investigate the thermal conductivity of silicon nanowires based on molecular dynamics (MD) simulations. The simulated thermal conductivities of nanowires with square cross sections are found to be about two orders of magnitude smaller than those of bulk Si crystals in a wide range of temperatures (200–500 K) for both rigid and free boundary conditions. A solution of the Boltzmann transport equation is used to explore the possibility of explaining the MD results based on boundary scattering. © 1999 American Institute of Physics.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
81.07.-b Nanoscale materials and structures: fabrication and characterization
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
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Stretching quantum wells: A method for trapping free carriers in GaAs heterostructures

V. Negoita, D. W. Snoke, and K. Eberl

Appl. Phys. Lett. 75, 2059 (1999); http://dx.doi.org/10.1063/1.124915 (3 pages) | Cited 30 times

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We have demonstrated a method of using inhomogeneous stress to create an in-plane harmonic potential in GaAs quantum wells which works equally well for excitons and for free conduction electrons. The depth of the well can be continuously varied via an external control. This essentially provides a type of gate for controlling the motion of carriers, e.g., a two-dimensional electron gas, without using electric field. © 1999 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Ey III-V semiconductors
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
71.35.-y Excitons and related phenomena
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Dislocation reduction in GaN thin films via lateral overgrowth from trenches

Y. Chen, R. Schneider, S. Y. Wang, R. S. Kern, C. H. Chen, and C. P. Kuo

Appl. Phys. Lett. 75, 2062 (1999); http://dx.doi.org/10.1063/1.124916 (2 pages) | Cited 22 times

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A technology to reduce the dislocation density in GaN thin films by lateral overgrowth from trenches (LOFT) is reported. In LOFT, a GaN thin film was grown on sapphire substrate first, then trenches were formed into the thin film by etching. GaN material was regrown laterally from the trench sidewalls to form a continuous thin film. The average surface density of threading dislocations is reduced from 8×109/cm2 in the first GaN thin film to 6×107/cm2 in the regrown GaN thin film. © 1999 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
81.05.Ea III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Effect of channel doping on the low-frequency noise in GaN/AlGaN heterostructure field-effect transistors

A. Balandin, S. Morozov, G. Wijeratne, S. J. Cai, R. Li, J. Li, K. L. Wang, C. R. Viswanathan, and Yu. Dubrovskii

Appl. Phys. Lett. 75, 2064 (1999); http://dx.doi.org/10.1063/1.124917 (3 pages) | Cited 15 times

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We examined low-frequency noise in doped and undoped channel GaN/AlGaN/SiC heterostructure field-effect transistors with different Al content in the barrier. The observed noise spectra follow the 1/fγ law with 0.8 ⩽ γ ⩽ 1.2 for frequencies f up to 100 kHz. Our results indicate two orders of magnitude reduction in the input-referred noise spectral density in the undoped channel devices with respect to the noise density in the doped channel devices of comparable electric characteristics. Low temperature measurements reveal generation—recombination-type peaks in the spectra of the doped channel devices. Effects of the piezoelectric charges at the GaN/AlGaN interface are also discussed. © 1999 American Institute of Physics.
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85.30.Tv Field effect devices
72.70.+m Noise processes and phenomena
81.05.Ea III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Photocurrent self-oscillations in a spatially direct GaAs/AlGaAs superlattice

A. M. Tomlinson, A. M. Fox, J. E. Cunningham, and W. Y. Jan

Appl. Phys. Lett. 75, 2067 (1999); http://dx.doi.org/10.1063/1.124918 (3 pages) | Cited 4 times

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We report the observation of self-sustained photocurrent oscillations in a weakly coupled spatially direct intrinsic GaAs/Al0.3Ga0.7As superlattice. The oscillations are attributed to the dynamics of unstable electric field domains related to the Γ−Γ e1-e2 tunneling resonance. The observed oscillation period is much longer than the carrier recombination time and the interwell tunneling time. The nonlinear behavior shows a complex dependence on the optical power and the external bias. © 1999 American Institute of Physics.
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73.50.Pz Photoconduction and photovoltaic effects
81.05.Ea III-V semiconductors
73.61.Ey III-V semiconductors
72.80.Ey III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
72.40.+w Photoconduction and photovoltaic effects
73.23.-b Electronic transport in mesoscopic systems

Elastic and plastic properties of GaN determined by nano-indentation of bulk crystal

R. Nowak, M. Pessa, M. Suganuma, M. Leszczynski, I. Grzegory, S. Porowski, and F. Yoshida

Appl. Phys. Lett. 75, 2070 (1999); http://dx.doi.org/10.1063/1.124919 (3 pages) | Cited 48 times

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Show Abstract
The major obstacle to the production of a blue laser is posed by difficulties with the preparation of defect-free GaN layers. A considerable amount of empirical work is presently being undertaken to achieve this goal. However, there is a lack of basic research on the reduction of residual stress and defects in these epilayers since the mechanical characteristics of GaN have not been measured yet. This is due to difficulties with experimental examination of thin films. This work addresses the mechanical properties of bulk GaN obtained by a high-pressure method. Young’s modulus (295 GPa), hardness (20 GPa), yield strength (15 GPa), and the stress–strain curve of GaN have been evaluated using nano-indentation. The cause of the sudden depth excursions during indentation of GaN epilayers has been clarified. © 1999 American Institute of Physics.
Show PACS
81.05.Ea III-V semiconductors
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
62.20.M- Structural failure of materials
62.20.Qp Friction, tribology, and hardness
68.35.Gy Mechanical properties; surface strains
62.20.F- Deformation and plasticity
62.20.D- Elasticity
68.60.Bs Mechanical and acoustical properties
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