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10 May 2004

Volume 84, Issue 19, pp. 3723-3937

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 3933 (2004); http://dx.doi.org/10.1063/1.1745103 (3 pages)

A. Cassinese, G. M. De Luca, A. Prigiobbo, M. Salluzzo, and R. Vaglio
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Determination of density profile of ultrathin SiO2/Si3N4/SiO2/Si(001) multilayer structures using x-ray reflectivity technique

S. Banerjee, S. Ferrari, R. Piagge, and S. Spandoni

Appl. Phys. Lett. 84, 3798 (2004); http://dx.doi.org/10.1063/1.1739519 (3 pages) | Cited 7 times

Online Publication Date: 29 April 2004

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In this report, we present an analysis of a SiO2/Si3N4/SiO2/Si(001) ultrathin multilayer structure using the x-ray reflectivity technique. The trilayer was grown using low-pressure chemical vapor deposition with each layer having a nominal thickness of ∼50 Å. Here, we propose an approach to analyze ultrathin multilayer films using two analysis schemes in tandem, i.e., distorted wave Born approximation and exact recursive formalism for x-ray reflectivity. We observe that, when SiO2 is deposited on a Si substrate, the electron density is lower than when it is deposited on Si3N4. We also observe that the two interfaces of the nitride (Si3N4) film are different, i.e., the interfacial width with the lower SiO2 is larger than the width with the top SiO2 layer. © 2004 American Institute of Physics.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
61.05.cm X-ray reflectometry (surfaces, interfaces, films)
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Propagation loss in GaN-based ridge waveguides

O. Skorka, B. Meyler, and J. Salzman

Appl. Phys. Lett. 84, 3801 (2004); http://dx.doi.org/10.1063/1.1741025 (3 pages) | Cited 5 times

Online Publication Date: 29 April 2004

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GaN ridge waveguides were fabricated by selective area growth in an organometallic vapor phase epitaxial system. The growth enhancement on a 3.5 μm wide exposed channel versus the masked area width was measured. The propagation losses of a series of GaN multimode waveguides, with different widths, were measured by the outscattering technique at λ=488 nm. The internal optical loss of the GaN ridge waveguide was found to be αint ∼ 4.45 cm−1. Sidewall scattering loss (αscat) and the additional optical loss due to metal electrodes were also measured. The fabricated waveguides may be a basic component for integrated optic circuits. © 2004 American Institute of Physics.
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42.81.Dp Propagation, scattering, and losses; solitons
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
42.79.Gn Optical waveguides and couplers
78.66.Fd III-V semiconductors
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Broadband 1400 nm emission from Ni2+ in zinc—alumino—silicate glass

Takenobu Suzuki and Yasutake Ohishi

Appl. Phys. Lett. 84, 3804 (2004); http://dx.doi.org/10.1063/1.1741027 (3 pages) | Cited 42 times

Online Publication Date: 29 April 2004

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Broadband near-infrared emission from Ni2+ in zinc–alumino–silicate glass was observed at room temperature. The emission band had a peak at ∼1400 nm with a bandwidth more than 300 nm, and covered the O, E, S, C, and L bands (1260–1625 nm). The emission lifetime was more than 200 μs even at room temperature. The observed near-infrared emission could be attributed to the 3A2g(3F)→3T1g(3F) transition of Ni2+ in octahedral sites. This nickel-doped glass can be expected as an amplification medium for tunable lasers and broadband optical amplifiers for the wavelength division multiplexing transmission system applications. © 2004 American Institute of Physics.
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78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.55.Qr Amorphous materials; glasses and other disordered solids
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Experimental investigation of coherent structures in a low-energy electron beam

G. Bettega, F. Cavaliere, A. Illiberi, R. Pozzoli, M. Romé, M. Cavenago, and Yu. Tsidulko

Appl. Phys. Lett. 84, 3807 (2004); http://dx.doi.org/10.1063/1.1741029 (3 pages) | Cited 5 times

Online Publication Date: 29 April 2004

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A sharp transition to a space-charge dominated regime is induced in a low-energy electron beam produced in a Malmberg–Penning trap by increasing the emission current of the source. The transition is characterized by the appearance of a region, around the axis of the beam, not accessible to beam electrons, and by the fast development of coherent structures in the remaining electron plasma, due to the sharp increase of local vorticity. The results are interpreted in the framework of a cold fluid drift–Poisson model, and using a three-dimensional particle-in-cell simulation code. © 2004 American Institute of Physics.
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29.25.Ni Ion sources: positive and negative
52.50.Dg Plasma sources
52.65.Rr Particle-in-cell method
52.59.Sa Space-charge-dominated beams
07.77.Ka Charged-particle beam sources and detectors
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Fabrication of ZnO quantum dots embedded in an amorphous oxide layer

Kyoung-Kook Kim, Nobuyuki Koguchi, Young-Woo Ok, Tae-Yeon Seong, and Seong-Ju Park

Appl. Phys. Lett. 84, 3810 (2004); http://dx.doi.org/10.1063/1.1741030 (3 pages) | Cited 53 times

Online Publication Date: 29 April 2004

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ZnO quantum dots (QDs) have been fabricated by the growth of SiO2/ZnO films/Si substrate and subsequent rapid-thermal annealing in a N2 ambient. Transmission electron microscopy (TEM) results show that the ZnO QDs 3–7 nm in size are formed and embedded in the amorphous silicon oxide interfacial layer when annealed at 850 °C. Photoluminescence (PL) at room temperature from the 850 °C-annealed samples reveals only high-energy emission at about 3.37 eV, while PL at 10 K shows a broad spectra with a tail up to about 3.5 eV. The TEM and PL results indicate that the broad spectra are caused by the presence of the ZnO QDs and hence by the quantum confinement effect. © 2004 American Institute of Physics.
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81.05.Dz II-VI semiconductors
81.07.Ta Quantum dots
78.66.Hf II-VI semiconductors
81.15.Cd Deposition by sputtering
68.37.Lp Transmission electron microscopy (TEM)
78.55.Et II-VI semiconductors
78.67.Hc Quantum dots
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Modification of the refractive index of lithium niobate crystals by transmission of high-energy 4He2+ and D+ particles

B. Andreas, K. Peithmann, K. Buse, and K. Maier

Appl. Phys. Lett. 84, 3813 (2004); http://dx.doi.org/10.1063/1.1741031 (3 pages) | Cited 11 times

Online Publication Date: 29 April 2004

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We report reductions of the refractive index of congruently melting lithium niobate crystals of up to 6×10−3 by exposure of z-cut samples with high-energy 4He2+ and D+ particles which are transmitted through the crystals. © 2004 American Institute of Physics.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
64.70.D- Solid-liquid transitions
61.80.Jh Ion radiation effects
61.82.Ms Insulators

Neutron reflectivity study of ultrathin SiO2 on Si

Valérie Bertagna, René Erre, Marie-Louise Saboungi, Sébastien Petitdidier, Didier Lévy, and Alain Menelle

Appl. Phys. Lett. 84, 3816 (2004); http://dx.doi.org/10.1063/1.1741034 (3 pages) | Cited 2 times

Online Publication Date: 29 April 2004

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Neutron reflectivity was applied to the study of ultrathin silicon oxide films, of interest due to the requirement for reduced dimensions of the elemental components in microelectronic devices [I. Eisele and W. Hansch, Thin Solid Films 369, 60 (2000); C. Battaglin et al., Thin Solid Films 351, 176 (1999)]. Silicon oxides were prepared using three different ways: Chemical, electrochemical, and thermal oxidation. From neutron reflectivity, it was possible to derive the oxide thickness, the Si/SiO2 interface roughness, and the density of the layer. In complementary measurements, the chemistry of the chemical and thermal surface layers was obtained by infrared spectroscopy. The anodic oxides were found to be as dense as thermal oxides, but the chemical one was less dense. This result was checked by Fourier transform infrared spectroscopy. © 2004 American Institute of Physics.
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78.66.Nk Insulators
81.65.Mq Oxidation
68.35.Ct Interface structure and roughness
78.30.Hv Other nonmetallic inorganics
81.05.Cy Elemental semiconductors
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Phonon–boundary scattering in ultrathin single-crystal silicon layers

W. Liu and M. Asheghi

Appl. Phys. Lett. 84, 3819 (2004); http://dx.doi.org/10.1063/1.1741039 (3 pages) | Cited 51 times

Online Publication Date: 29 April 2004

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Thermal engineering of many nanoscale sensors, actuators, and high-density thermomechanical data storage devices, as well as the self-heating in deep submicron transistors, are largely influenced by thermal conduction in ultrathin silicon layers. The present study measures the lateral thermal conductivity of single-crystal silicon layers of thicknesses 20 and 100 nm at temperatures between 20 and 300 K, using Joule heating and electrical–resistance thermometry in suspended microfabricated structures. The thermal conductivity of the 20 nm thick silicon layer is ∼22 W m−1 K−1, which is nearly an order of magnitude smaller than the bulk value at room temperature. In general, a large reduction in thermal conductivity resulting from phonon–boundary scattering, particularly at low temperatures, is observed. It appears that the classical thermal conductivity theory that accounts for the reduced phonon mean-free paths based on a solution of the Boltzmann transport equation along a layer is able to capture the ballistic, or nonlocal, phonon transport in ultrathin silicon films. © 2004 American Institute of Physics.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
63.20.K- Phonon interactions
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High-performance polycrystalline silicon thin-film transistor with multiple nanowire channels and lightly doped drain structure

Yung-Chun Wu, Ting-Chang Chang, Chun-Yen Chang, Chi-Shen Chen, Chun-Hao Tu, Po-Tsun Liu, Hsiao-Wen Zan, and Ya-Hsiang Tai

Appl. Phys. Lett. 84, 3822 (2004); http://dx.doi.org/10.1063/1.1745104 (3 pages) | Cited 13 times

Online Publication Date: 29 April 2004

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This investigation examines polycrystalline silicon thin-film transistors (TFTs) with multiple nanowire channels and a lightly doped drain (LDD). A device with an LDD structure exhibits low leakage current because the lateral electrical field is reduced in the drain offset region. Additionally, multiple nanowire channels can generate fewer defects in the polysilicon grain boundary and have more efficient NH3 plasma passivation than single-channel TFTs, further reducing leakage current. They exhibit superior electrical characteristics to those of single-channel TFTs, such as a higher ON/OFF current ratio (>108), a better subthreshold slope of 110 mV/decade, an absence of drain-induced barrier lowering, and suppressed kink-effect. Devices with the proposed TFTs are highly promising for use in active-matrix liquid-crystal display technologies. © 2004 American Institute of Physics.
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85.30.Tv Field effect devices
81.05.Cy Elemental semiconductors
81.65.Rv Passivation
61.72.Mm Grain and twin boundaries
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Hydrogen-induced degradation in epitaxial and polycrystalline (Ba,Sr)TiO3 thin films

Jang-Sik Lee, Y. Li, Y. Lin, Sang Yeol Lee, and Q. X. Jia

Appl. Phys. Lett. 84, 3825 (2004); http://dx.doi.org/10.1063/1.1745105 (3 pages) | Cited 12 times

Online Publication Date: 29 April 2004

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A comparative study of hydrogen-induced degradation in epitaxial and polycrystalline (Ba,Sr)TiO3 (BST) thin films has been carried out. Epitaxial BST was prepared on SrRuO3 (SRO)/SrTiO3 (STO), whereas polycrystalline BST was deposited on SRO/SiOx/Si. After the Pt top electrode deposition, we have measured the dielectric response and leakage current characteristics before and after annealing in forming gas (6% hydrogen/94% argon) at 450 °C for 1 h. Even though both samples have the same capacitor architecture, Pt/BST/SRO, the degree of degradation after annealing in forming gas was found to be quite different. Epitaxial BST films were highly immune to hydrogen degradation; however, polycrystalline BST films degraded severely in terms of both dielectric and electrical properties. We show that the grain boundary is one of the main sources of hydrogen-induced degradation. © 2004 American Institute of Physics.
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77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
61.72.Mm Grain and twin boundaries
68.35.Fx Diffusion; interface formation
77.22.Ch Permittivity (dielectric function)
81.40.Gh Other heat and thermomechanical treatments
81.15.Fg Pulsed laser ablation deposition
81.15.Cd Deposition by sputtering
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Large effects due to electron–phonon-impurity interference in the resistivity of Pt/C-Ga composite nanowires

J.-F. Lin, J. P. Bird, L. Rotkina, A. Sergeev, and V. Mitin

Appl. Phys. Lett. 84, 3828 (2004); http://dx.doi.org/10.1063/1.1745108 (3 pages) | Cited 18 times

Online Publication Date: 29 April 2004

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The temperature-dependent resistivity of highly disordered Pt/C-Ga composite nanowires is shown to be well described by the interference of electron–phonon scattering and elastic electron scattering from boundaries and defects. The strongly disordered nature of these wires, combined with a high value of their Debye temperature, are responsible for the pronounced nature of the interference effects in their resistivity. © 2004 American Institute of Physics.
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73.63.Nm Quantum wires
63.20.K- Phonon interactions
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
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Room-temperature growth of a carbon nanofiber on the tip of conical carbon protrusions

Masaki Tanemura, T. Okita, H. Yamauchi, S. Tanemura, and R. Morishima

Appl. Phys. Lett. 84, 3831 (2004); http://dx.doi.org/10.1063/1.1745109 (3 pages) | Cited 36 times

Online Publication Date: 29 April 2004

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Glassy carbon was Ar+-ion bombarded with a simultaneous Mo supply under ultrahigh vacuum conditions using a microprotrusion fabrication system that consists of a differentially pumped ion gun and a seed-material supply source. Conical protrusions were formed by sputtering with a seed supply, and carbon nanofibers (CNFs) grew on the tips even at room temperature. The length of CNFs reached up to ∼10 μm, and their diameter was almost uniform (50 nm) in the growth direction. The short CNFs aligned in the ion beam direction, whereas the long ones were non-aligned. The CNF growth on a glassy carbon surface was ascribed to the enhanced surface texturing and to the massive redeposition of C atoms onto cones, both of which are specific to the oblique ion bombardment: The former would lead to an increase in the number of possible nucleation sites for the CNF growth, and the C atoms arising from the latter process would migrate toward the conical tips, thus forming CNFs. © 2004 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.05.U- Carbon/carbon-based materials
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.43.Er Other amorphous solids
61.80.Jh Ion radiation effects
64.60.Q- Nucleation
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.07.-b Nanoscale materials and structures: fabrication and characterization
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Size dependence of the work function in InAs quantum dots on GaAs(001) as studied by Kelvin force probe microscopy

T. Yamauchi, M. Tabuchi, and A. Nakamura

Appl. Phys. Lett. 84, 3834 (2004); http://dx.doi.org/10.1063/1.1745110 (3 pages) | Cited 10 times

Online Publication Date: 29 April 2004

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We have investigated a work function of single InAs quantum dots (QDs) on GaAs(001) correlating with the dot size by means of Kelvin force probe microscopy. The observed contact potential difference (CPD) of the single QD is lower than that of an InAs wetting layer, and increases with decreasing QD height. The height dependence of the CPD is well interpreted in terms of the quantum size effect by which the amount of accumulated charges in the QD is determined through the confinement energy levels in the QD. © 2004 American Institute of Physics.
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73.21.La Quantum dots
73.40.Cg Contact resistance, contact potential
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ps Atomic force microscopy (AFM)
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A hybrid Al0.10Ga0.90As/AlAs bilayer electron system with tunable g-factor

E. P. De Poortere and M. Shayegan

Appl. Phys. Lett. 84, 3837 (2004); http://dx.doi.org/10.1063/1.1745111 (3 pages) | Cited 4 times

Online Publication Date: 29 April 2004

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We have fabricated a device composed of two closely coupled two-dimensional electron systems, one of which resides within an AlAs quantum well at the X point of the Brillouin zone, while the other is contained at the Γ point in the alloy Al0.10Ga0.90As, grown directly below the AlAs. The electronic properties of these two systems are strongly asymmetric: the respective cyclotron masses in the AlAs and the Al0.10Ga0.90As layers, measured in units of the free electron mass, are ∼ 0.5 and 0.07, while the effective electron g-factors are approximately 7 and 0. With the help of front and back gates, we can confine mobile carriers to either or both of the two quantum wells, as confirmed by magnetotransport measurements. © 2004 American Institute of Physics.
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73.21.Fg Quantum wells
68.65.Fg Quantum wells
72.20.My Galvanomagnetic and other magnetotransport effects
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
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Exchange bias of antiferromagnets with random anisotropies and perfectly compensated interfaces

T. Mewes and R. L. Stamps

Appl. Phys. Lett. 84, 3840 (2004); http://dx.doi.org/10.1063/1.1745112 (3 pages) | Cited 4 times

Online Publication Date: 29 April 2004

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An alternative mechanism for exchange bias for ferromagnet/antiferromagnet bilayers with completely compensated interfaces is proposed and analyzed within the biquadratic coupling model. We show that a distribution of anisotropies in the antiferromagnet can lead to the appearance of exchange bias in a bilayer with a perfectly compensated interface without defects. The energy associated with the unidirectional anisotropy that gives rise to the shifted hysteresis curve is stored in antiferromagnetic domain walls between regions in the antiferromagnet with different anisotropy. This mechanism also leads naturally to an enhanced coercivity of the ferromagnet which is caused by the anisotropy in the antiferromagnet. © 2004 American Institute of Physics.
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75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.50.Ee Antiferromagnetics
75.30.Et Exchange and superexchange interactions
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Blue-light emission from sputtered Ti:SiO2 films without annealing

Osamu Hanaizumi, Kazutaka Ono, Yuichi Ogawa, Toshiaki Matsumoto, Hidehiko Yoda, and Kazuo Shiraishi

Appl. Phys. Lett. 84, 3843 (2004); http://dx.doi.org/10.1063/1.1745113 (3 pages) | Cited 3 times

Online Publication Date: 29 April 2004

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Blue-light emission from Ti:SiO2 sputtered films was observed at room temperature without annealing and it could be seen by the naked eye. The peaks of photoluminescence spectra were located at 3.03–3.05 eV and full width at half maximum ranged from 0.38–0.40 eV, which were almost the same in samples having different energies of absorption edge. SiOx layers may contribute to emission, which are interfacial regions between Ti particles and surrounding SiO2 medium, and the size of Ti particles may affect the efficiency of emission.© 2004 American Institute of Physics.
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78.66.Nk Insulators
78.55.Hx Other solid inorganic materials
68.55.A- Nucleation and growth
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Evaluation of manganite films on silicon for uncooled bolometric applications

R. J. Choudhary, Anjali S. Ogale, S. R. Shinde, S. Hullavarad, S. B. Ogale, T. Venkatesan, R. N. Bathe, S. I. Patil, and Ravi Kumar

Appl. Phys. Lett. 84, 3846 (2004); http://dx.doi.org/10.1063/1.1748837 (3 pages) | Cited 22 times

Online Publication Date: 29 April 2004

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Pulsed-laser-deposited polycrystalline/amorphous films of mixed-valent manganites [La0.7Ca0.3MnO3 (LCMO), La0.5Sr0.5MnO3 (LSMO), La0.5Ba0.5MnO3 (LBMO), and (La0.6Pr0.4)0.67Ca0.33MnO3 (LPCMO)] grown at low temperature (450 °C) on single crystal (001) silicon substrate are evaluated for uncooled bolometric applications. It is shown that the temperature coefficient of resistance (TCR) and electrical noise (Sv) depend on the chemical composition. The optimum performance is found for LCMO with TCR of ∼7% K−1 and spectral noise ∼ 8.9×10−13 V2/Hz. In LBMO and LSMO the noise is much lower, but so is the TCR (1.5%–2% K−1). In LPCMO the TCR is high ( ∼ 10% K−1) and the noise is as well. © 2004 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
73.61.Ng Insulators
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
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Observation of nonequilibrium longitudinal optical phonons in InN and its implications

W. Liang, K. T. Tsen, D. K. Ferry, Hai Lu, and William J. Schaff

Appl. Phys. Lett. 84, 3849 (2004); http://dx.doi.org/10.1063/1.1748838 (3 pages) | Cited 2 times

Online Publication Date: 29 April 2004

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Nonequilibrium longitudinal optical phonons in a high quality, single crystal wurtzite structure InN sample have been studied by picosecond Raman spectroscopy. Our experimental results demonstrate that the band gap of InN cannot be around 1.89 eV; but are consistent with a band gap of about 0.8 eV. In addition, they disprove the idea that 0.8 eV luminescence observed recently in InN is due to deep level radiative emission in InN. © 2004 American Institute of Physics.
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78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics

Electroluminescence as internal light source for measurement of the photonic strength of random porous GaP

A. F. van Driel, D. Vanmaekelbergh, and J. J. Kelly

Appl. Phys. Lett. 84, 3852 (2004); http://dx.doi.org/10.1063/1.1748839 (3 pages) | Cited 5 times

Online Publication Date: 29 April 2004

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During porous etching of GaP, electroluminescence ranging from the ultraviolet to the near-infrared is generated at the interface of the porous and the nonporous layer. This is used to measure the wavelength-dependent transmission of light through porous layers in a wide thickness range. Two types of porous structures, characterized by different pore sizes, were studied. The transmission of the emitted light gives valuable information about wavelength-dependent diffusion of light through porous GaP. © 2004 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.05.Rm Porous materials; granular materials
78.60.Fi Electroluminescence
81.65.Cf Surface cleaning, etching, patterning
78.40.Ha Other nonmetallic inorganics
78.30.Fs III-V and II-VI semiconductors
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Intense longitudinal electric fields generated from transverse electromagnetic waves

Godai Miyaji, Noriaki Miyanaga, Koji Tsubakimoto, Keiichi Sueda, and Ken Ohbayashi

Appl. Phys. Lett. 84, 3855 (2004); http://dx.doi.org/10.1063/1.1748843 (3 pages) | Cited 20 times

Online Publication Date: 29 April 2004

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We present a simple method for generating an intense longitudinal electric field from transverse electromagnetic waves (laser pulses) with radially symmetric polarization, to which a liquid crystal device converts linear polarization with energy efficiency of ∼ 99%. The laser-generated longitudinal electric field was observed in two dimensions and distinguished from the transverse component using the optical Kerr shutter method. The measured amplitude was 1.1 GV/m at the focus of a pulsed Nd:YAG laser beam of 0.25-MW peak-power. © 2004 American Institute of Physics.
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42.62.-b Laser applications
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
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Emission from the higher-order excitons in ZnO films grown by laser molecular-beam epitaxy

A. Tsukazaki, A. Ohtomo, M. Kawasaki, T. Makino, C. H. Chia, Y. Segawa, and H. Koinuma

Appl. Phys. Lett. 84, 3858 (2004); http://dx.doi.org/10.1063/1.1748847 (3 pages) | Cited 17 times

Online Publication Date: 29 April 2004

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Epitaxial ZnO thin films were grown by laser molecular-beam epitaxy on lattice-matched ScAlMgO4 substrates following the deposition and annealing of suitable buffer layers. The samples were characterized by low-temperature photoluminescence (PL), absorption, and reflectivity measurements. PL from higher order (n = 2) excitons (A exciton) was observed at temperatures lower than 40 K. The absorption spectrum contained lines and the reflection spectrum exhibited anomalies that were assigned to the excited-states (n = 2,3) of A and B excitons. The optical quality could be improved dramatically by using annealed ZnO or MgZnO buffer layers. © 2004 American Institute of Physics.
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71.35.Aa Frenkel excitons and self-trapped excitons
78.66.Hf II-VI semiconductors
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Reduced threshold current of a quantum dot laser in a short period superlattice of indirect-band gap

Gregory Sun, Richard A. Soref, and Jacob B. Khurgin

Appl. Phys. Lett. 84, 3861 (2004); http://dx.doi.org/10.1063/1.1751606 (3 pages) | Cited 4 times

Online Publication Date: 29 April 2004

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We propose the idea of making quantum dot lasers by embedding direct-band gap quantum dots in a short period superlattice whose band gap is indirect. This technique reduces the threshold current and its temperature dependence. We show that a higher characteristic-temperature T0 can be achieved in a quantum dot laser with indirect GaAs/AlAs superlattice barriers compared to that with direct GaAs barriers. © 2004 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
73.63.Kv Quantum dots
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A prototype microthermophotovoltaic power generator

W. M. Yang, S. K. Chou, C. Shu, Z. W. Li, and H. Xue

Appl. Phys. Lett. 84, 3864 (2004); http://dx.doi.org/10.1063/1.1751614 (3 pages) | Cited 17 times

Online Publication Date: 29 April 2004

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A prototype microthermophotovoltaic (micro-TPV) power generator is described in this letter. The system is made of a SiC (silicon carbide) emitter, a simple nine-layer dielectric filter, and a GaSb (gallium antimony) photovoltaic cell array. In a microcombustor of 0.113 cm3 in volume, when the flow rate of hydrogen is 4.20 g/h, the micro-TPV system is able to deliver an electrical power output of 1.02 W, corresponding to an open-circuit electrical voltage of 2.28 V and a short-circuit current of 0.59 A. The prototype of the micro-TPV system will make it possible for us to substitute batteries with micropower generators in micromechanical devices in the near future. © 2004 American Institute of Physics.
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84.60.Jt Photoelectric conversion
85.80.-b Thermoelectromagnetic and other devices
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Self-assembled growth and optical emission of silver-capped silicon nanowires

T. Qiu, X. L. Wu, X. Yang, G. S. Huang, and Z. Y. Zhang

Appl. Phys. Lett. 84, 3867 (2004); http://dx.doi.org/10.1063/1.1753063 (3 pages) | Cited 24 times

Online Publication Date: 29 April 2004

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Structured silver-capped silicon nanowires were fabricated via electroless metal deposition on a silicon wafer in an ionic silver HF solution through selective chemical etching. Their formation mechanism was explained on the basis of self-assembled localized microscopic electrochemical cell model. The metal–semiconductor composite nanostructure was found to have a strong ultraviolet-emitting property with an emission peak position at 330 nm. The intensity of the peak nonmonotonously varies with annealing temperature and time, but its position remains unchanged. Emission and excitation spectral analyses suggest that the ultraviolet emission is closely related to the existence of silver vacancy defects in silver nanocaps formed during sample fabrication. A specific vacancy density is required to produce the strong ultraviolet emission. © 2004 American Institute of Physics.
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78.67.Lt Quantum wires
81.16.Dn Self-assembly
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Type-II interband transition of ZnS0.78Te0.22/ZnTe single quantum wells

Jae Ho Bahng, S. J. Moon, K. H. Lee, J. C. Choi, K. Jeong, and H. L. Park

Appl. Phys. Lett. 84, 3870 (2004); http://dx.doi.org/10.1063/1.1728306 (3 pages) | Cited 8 times

Online Publication Date: 29 April 2004

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Optical properties of ZnS0.78Te0.22/ZnTe single quantum wells grown on GaAs (100) substrates by hot wall epitaxy technique with varying the ZnS0.78Te0.22 well width from 0.3 to 1.8 nm were investigated by photoluminescence (PL) measurements at low temperature and by temperature-dependent PL measurements. PL results show the evidence of type-II transition and their peak energy shifts to higher energies as the ZnS0.78Te0.22 well width decreases. In addition, temperature-dependent PL measurements show the increase of the activation energy as the well thickness decreases, indicating the increase of confinement effect. This study makes it possible to introduce proper band diagram for this structure, and can give very useful information on their device applications. © 2004 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
73.21.Fg Quantum wells
78.67.De Quantum wells
68.55.A- Nucleation and growth
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.07.St Quantum wells
81.05.Dz II-VI semiconductors
71.20.Nr Semiconductor compounds
73.20.At Surface states, band structure, electron density of states
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