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15 Jul 2002

Volume 81, Issue 3, pp. 391-566

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Enhancement of the optical nonlinearity in pseudoisocyanine J aggregates embedded in distributed feedback microcavities

F. Sasaki, S. Kobayashi, and S. Haraichi

Appl. Phys. Lett. 81, 391 (2002); http://dx.doi.org/10.1063/1.1493643 (3 pages) | Cited 7 times

Online Publication Date: 2 July 2002

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Coherent transients of pseudoisocyanine J aggregates in distributed feedback microcavities are reported. Under the resonant excitation of the cavity-mode observed at the low-energy side of the excitonic resonance, the response time is about 0.5 ps, approximately equal to the pump–pulse duration. We find the enhancement of the optical nonlinearity by one order of magnitude in the microcavity. The excitation of the dielectric-band mode is effective to enhance the nonlinearity with the ultrafast response. © 2002 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
42.65.Pc Optical bistability, multistability, and switching, including local field effects
71.35.-y Excitons and related phenomena

Long-lasting phosphorescence in Sn2+–Cu2+ codoped silicate glass and its high-pressure treatment effect

Jianbei Qiu, Koichi Miyauchi, Yoji Kawamoto, Naoyuki Kitamura, Jianrong Qiu, and Kazuyuki Hirao

Appl. Phys. Lett. 81, 394 (2002); http://dx.doi.org/10.1063/1.1493664 (3 pages) | Cited 3 times

Online Publication Date: 2 July 2002

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Long-lasting phosphorescence was observed at 510 nm in a Sn2+–Cu2+ codoped Na2O–CaO–SiO2 glass at room temperature under UV illumination of 254 nm. When the glass was compressed under 3, 6, and 9 GPa, the phosphorescence shifted to 465 nm and its decay rate became shorter. The optical absorption spectra of the samples changed after compression, showing that the cupric ions were reduced to the cuprous ions. The high-pressure treatment also resulted in a lower-energy shift in the absorption edge. It was suggested that Sn2+ ions act as hole trapping centers, while oxygen vacancies surrounding by Ca2+ ions as well as active sites in the glass matrix, i.e., as electron trapping centers. © 2002 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
81.05.Kf Glasses (including metallic glasses)
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
81.40.Vw Pressure treatment
78.60.-b Other luminescence and radiative recombination
62.50.-p High-pressure effects in solids and liquids
81.40.Tv Optical and dielectric properties related to treatment conditions
78.40.Pg Disordered solids
71.55.Jv Disordered structures; amorphous and glassy solids
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Room temperature type-II interband cascade laser

Rui Q. Yang, J. L. Bradshaw, J. D. Bruno, J. T. Pham, D. E. Wortman, and R. L. Tober

Appl. Phys. Lett. 81, 397 (2002); http://dx.doi.org/10.1063/1.1494455 (3 pages) | Cited 18 times

Online Publication Date: 2 July 2002

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A mid-IR (3.3–3.5 μm) type-II interband cascade laser has been demonstrated at temperatures up to 300 K in pulsed mode and 150 K in cw mode. Threshold current densities as low as 13.2 A/cm2 and power efficiencies as large as 17% have been achieved under cw conditions at 80 K. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.60.Pk Continuous operation
42.60.By Design of specific laser systems

Influence of leakage current on temperature performance of GaAs/AlGaAs quantum cascade lasers

D. Indjin, P. Harrison, R. W. Kelsall, and Z. Ikonić

Appl. Phys. Lett. 81, 400 (2002); http://dx.doi.org/10.1063/1.1494457 (3 pages) | Cited 24 times

Online Publication Date: 2 July 2002

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A detailed analysis of intersubband electron scattering transport in GaAs/AlGaAs quantum cascade lasers (QCLs) is presented, using a full self-consistent rate equation model. Our approach includes all relevant scattering mechanisms between injector/collector, active region and continuumlike states in the cascade structures. In particular, the influence of the Al mole fraction in the quantum barriers on QCLs performance is investigated, by studying GaAs/AlGaAs structures with 33% and 45% Al barrier compositions, respectively. Excellent qualitative and quantitative agreement with recent experimental results at cryogenic and room temperatures is obtained. The model reproduces the gain saturation reported for the 33% Al device, which precludes laser operation at room temperature, and also the much improved room-temperature performance of the 45% Al device, with calculated 300 K threshold current of 17 kA/cm2, and confirms that the superior performance of the 45% Al device is due to suppression of parasitic conduction through continuum states as a consequence of the increased barrier height. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Amplification of ultrashort laser pulses in the photolytically driven XeF(C–A) active medium

V. I. Tcheremiskine, M. L. Sentis, and L. D. Mikheev

Appl. Phys. Lett. 81, 403 (2002); http://dx.doi.org/10.1063/1.1490403 (3 pages) | Cited 14 times

Online Publication Date: 2 July 2002

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Amplification of ultrashort laser pulses is demonstrated in a gas medium of the photolytical XeF(C–A) laser. A gas mixture of XeF2:N2:Ar was excited by vacuum-ultraviolet radiation produced by a high-current multichannel sliding discharge, which was initiated along one side of dielectric laser cavity. A small-signal gain of 1.6×10−3 cm−1 is observed for a seed pulse at 488 nm with ∼ 150 fs duration. The use of a second optical source together with the device optimization promise a multiple increase in the gain and the obtaining of high-contrast TW femtosecond pulses as a result of direct amplification, without application of a stretching/compression technique. © 2002 American Institute of Physics.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.55.Lt Gas lasers including excimer and metal-vapor lasers

High power and high brightness from an optically pumped InAs/InGaSb type-II midinfrared laser with low confinement

R. Kaspi, A. Ongstad, G. C. Dente, J. Chavez, M. L. Tilton, and D. Gianardi

Appl. Phys. Lett. 81, 406 (2002); http://dx.doi.org/10.1063/1.1493227 (3 pages) | Cited 25 times

Online Publication Date: 2 July 2002

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We report on optically pumped semiconductor lasers emitting near 3.8 μm that exhibit high power and low output divergence. The lasers incorporate multiple InAs/InGaSb/InAs type-II wells imbedded in an InGaAsSb waveguide that is designed to absorb the pump emission. When operated at 85 K, 0.25 mm×2.5 mm broad area devices produce >5 W of peak power under long pulse conditions. Moreover, these extremely bright devices exhibit a fast axis divergence of only ∼ 15° full width at half maximum (FWHM), coupled with a slow axis divergence of ∼ 6° FWHM. The first is due to the reduced optical confinement in the transverse direction, while the latter is attributed to the suppression of filament formation, which is another beneficial consequence of the low optical confinement. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.67.De Quantum wells
42.60.By Design of specific laser systems
81.07.St Quantum wells
81.05.Ea III-V semiconductors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Silicon-based optical waveguide polarizer using photonic band gap

Dengtao Zhao, Bin Shi, Zuimin Jiang, Yongliang Fan, and Xun Wang

Appl. Phys. Lett. 81, 409 (2002); http://dx.doi.org/10.1063/1.1494454 (3 pages) | Cited 3 times

Online Publication Date: 2 July 2002

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Based on different photonic band structures of TE and TM polarization modes in periodic multilayers, a method to realize the waveguide polarizer is proposed. The waveguide structure contains a SiO2 core layer sandwiched between two multilayers of alternately stacked poly-Si and SiO2, and the whole structure can be grown on a Si substrate. Its propagation characteristics are studied theoretically. High extinction ratio over 40 dB at a light wavelength of 1.3 μm is expected in the waveguide of only 40 μm long, accompanied with very low propagation loss of the passive TE mode. These characteristics are very suitable for the applications in integrated optics. The fabrication of this polarizer structure by using the magnetron sputtering method is demonstrated. © 2002 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays
42.70.Qs Photonic bandgap materials
42.79.Ci Filters, zone plates, and polarizers
42.50.-p Quantum optics
81.15.Cd Deposition by sputtering
78.66.Db Elemental semiconductors and insulators
81.05.Cy Elemental semiconductors

Room-temperature polariton lasers based on GaN microcavities

Guillaume Malpuech, Aldo Di Carlo, Alexey Kavokin, Jeremy J. Baumberg, Marian Zamfirescu, and Paolo Lugli

Appl. Phys. Lett. 81, 412 (2002); http://dx.doi.org/10.1063/1.1494126 (3 pages) | Cited 82 times

Online Publication Date: 2 July 2002

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The critical temperature for Bose condensation of exciton polaritons in an AlGaN microcavity containing 9 GaN quantum wells is calculated to be T = 460 K. We have modeled the kinetics of polaritons in such a microcavity device using the two-dimensional Boltzmann equation. Room-temperature lasing is found with a threshold as small as 100 mW. The kinetic blocking of polariton relaxation that prevents formation of the Bose-condensed phase of polaritons at low temperatures disappears at high temperatures, especially in n-doped samples. Thus, GaN microcavities are excellent candidates for realization of room-temperature polariton lasers. © 2002 American Institute of Physics.
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42.55.Sa Microcavity and microdisk lasers
42.55.Px Semiconductor lasers; laser diodes
78.67.De Quantum wells
81.05.Ea III-V semiconductors
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.21.Fg Quantum wells
71.35.-y Excitons and related phenomena
03.75.Hh Static properties of condensates; thermodynamical, statistical, and structural properties
03.75.Kk Dynamic properties of condensates; collective and hydrodynamic excitations, superfluid flow
37.10.Vz Mechanical effects of light on atoms, molecules, and ions
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.30.De Semiconductor-device characterization, design, and modeling

Light amplification and gain in polyfluorene waveguides

George Heliotis, Donal D. C. Bradley, Graham A. Turnbull, and Ifor D. W. Samuel

Appl. Phys. Lett. 81, 415 (2002); http://dx.doi.org/10.1063/1.1494473 (3 pages) | Cited 78 times

Online Publication Date: 2 July 2002

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We report a study of the properties of the semiconducting polymer poly(9,9-dioctylfluorene) (PFO) as a gain medium. We demonstrate amplification of blue light via amplified spontaneous emission (ASE) measurements on optically pumped PFO planar asymmetric waveguides. We show that the ASE wavelength can be tuned over a range of 20 nm by altering the supported waveguide modes. Gain/loss measurements at the peak ASE wavelength (466 nm) show that the waveguides can exhibit a large net gain of up to 74 cm−1 and have a very low loss coefficient ∼3 cm−1. These characteristics make PFO attractive as a high gain medium for short-wavelength lasers and optical amplifiers. © 2002 American Institute of Physics.
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42.82.Et Waveguides, couplers, and arrays
42.70.Jk Polymers and organics
78.45.+h Stimulated emission
42.82.Bq Design and performance testing of integrated-optical systems
42.79.Gn Optical waveguides and couplers
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Absolute density measurements of ammonia produced via plasma-activated catalysis

P. Vankan, T. Rutten, S. Mazouffre, D. C. Schram, and R. Engeln

Appl. Phys. Lett. 81, 418 (2002); http://dx.doi.org/10.1063/1.1494104 (3 pages) | Cited 9 times

Online Publication Date: 2 July 2002

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The generation of ammonia from atomic hydrogen and nitrogen has been demonstrated by means of cavity enhanced absorption spectroscopy. The atomic species are produced in a thermal plasma source in which plasma is created from mixtures of hydrogen and nitrogen. It is shown that for large atomic flux conditions, 2% of the hydrogen and nitrogen can be converted to ammonia. The process in which the ammonia molecules are formed from atomic radicals at the fully covered surface is called plasma-activated catalysis. © 2002 American Institute of Physics.
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52.77.-j Plasma applications
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
52.40.Hf Plasma-material interactions; boundary layer effects
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.50.Dg Plasma sources
52.75.Xx Thermionic and filament-based sources (e.g., Q machines, double- and triple-plasma devices, etc.)
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
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Anelastic deformation of Pb(Zr,Ti)O3 thin films by non-180° ferroelectric domain wall movements during nanoindentation

M. Algueró, A. J. Bushby, M. J. Reece, and A. Seifert

Appl. Phys. Lett. 81, 421 (2002); http://dx.doi.org/10.1063/1.1491291 (3 pages) | Cited 6 times

Online Publication Date: 2 July 2002

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Lead zirconate titanate Pb(Zr,Ti)O3 ferroelectric thin films show significant anelastic deformation when indented with spherical tipped indenters. Experiments on films with different Zr/Ti ratio and a mixed 〈001〉,〈100〉 preferred crystallographic orientation have shown that there is a good agreement between the anelastic deformation and the maximum strain achievable by non-180° domain wall movement. An expected increase of the indentation stiffness of the films also accompanies the anelastic deformation because of the single crystal elastic anisotropy. All these observations seem to indicate that non-180° ferroelectric domain wall movements occur under indentation stresses and cause anelasticity. Stresses for maximum anelastic deformation are compared with those for recently reported stress-induced depolarization. © 2002 American Institute of Physics.
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62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
68.60.Bs Mechanical and acoustical properties
77.80.Dj Domain structure; hysteresis
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
62.20.M- Structural failure of materials
62.20.Qp Friction, tribology, and hardness
68.35.Gy Mechanical properties; surface strains
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
68.55.-a Thin film structure and morphology
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
62.20.D- Elasticity

Low-threshold blue amplified spontaneous emission in a statistical copolymer and its blend

Tae-Woo Lee, O Ok Park, Dong Hoon Choi, Hyun Nam Cho, and Young Chul Kim

Appl. Phys. Lett. 81, 424 (2002); http://dx.doi.org/10.1063/1.1491297 (3 pages) | Cited 10 times

Online Publication Date: 2 July 2002

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We report low-threshold, blue amplified spontaneous emission (ASE) in a statistical copolymer, poly(9,9-dihexylfluorene-2,7-divinylene-m-phenylenevinylene-stat-p-phenylenevinylene) (CPDHFPV) and its blend with poly(9-vinylcarbazole) (PVK). PVK and CPDHFPV acted as the donor and the acceptor of the Förster-type excitation energy transfer, respectively. A single component waveguide made of CPDHFPV gave the threshold energy of 160 nJ/cm2/pulse. Moreover, that of the PVK/CPDHFPV (95/5 by wt.) blend device was as low as 20 nJ/cm2/pulse. From the relationship between the ASE intensity and the film thickness, we suggest that the optimum thickness for the photopumped ASE should be the transverse electric-mode cutoff thickness. © 2002 American Institute of Physics.
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78.45.+h Stimulated emission
42.70.Jk Polymers and organics

Effect of electrical boundary conditions on ferroelectric domain structures in thin films

Y. L. Li, S. Y. Hu, Z. K. Liu, and L. Q. Chen

Appl. Phys. Lett. 81, 427 (2002); http://dx.doi.org/10.1063/1.1492025 (3 pages) | Cited 50 times

Online Publication Date: 2 July 2002

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The domain structures in a ferroelectric thin film are studied using a phase-field model. A cubic-to-tetragonal ferroelectric phase transition in lead titanate thin film is considered. Both elastic interactions and electrostatic interactions are taken into account. The focus is on the effect of electrical boundary conditions on the domain morphologies and volume fractions. It is shown that different electric boundary conditions may have a significant effect on the domain structures. © 2002 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.80.Dj Domain structure; hysteresis
77.80.B- Phase transitions and Curie point
77.22.Ej Polarization and depolarization

Analysis of SiO2/Si(001) interface roughness for thin gate oxides by scanning tunneling microscopy

Masahide Gotoh, Koichi Sudoh, Hiroyasu Itoh, Kazunori Kawamoto, and Hiroshi Iwasaki

Appl. Phys. Lett. 81, 430 (2002); http://dx.doi.org/10.1063/1.1494124 (3 pages) | Cited 4 times

Online Publication Date: 2 July 2002

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We studied the interface roughnesses of SiO2/Si(001) for gate oxides of 8 and 15 nm thicknesses together with RCA-treated samples by using scanning tunneling microscopy (STM). By STM observation and scaling analysis we made clear that the interface roughnesses of thermal oxides/Si substrates were similar to each other and to that of the chemical oxide/Si substrate prior to thermal oxidation; the correlation length was 23–26 nm and the rms roughness at length scales larger than the correlation length was 0.28–0.29 nm. The results indicate that the interface roughnesses of the oxides are determined by the processes prior to the oxidations. © 2002 American Institute of Physics.
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81.65.Mq Oxidation
81.05.Cy Elemental semiconductors
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.35.Ct Interface structure and roughness
68.35.B- Structure of clean surfaces (and surface reconstruction)

Growth of single-wall carbon nanotubes within an ordered array of nanosize silica spheres

A. Lan, Z. Iqbal, A. Aitouchen, M. Libera, and H. Grebel

Appl. Phys. Lett. 81, 433 (2002); http://dx.doi.org/10.1063/1.1492846 (3 pages) | Cited 14 times

Online Publication Date: 2 July 2002

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Single-wall carbon nanotubes (SWCNTs), which were well-separated individuals or, small bundles of two to five tubes, were produced in a controllable manner by disproportionation of CO at 700 °C and 1 atm in the voids of an ordered array of silica spheres with embedded bimetallic Mo/Co catalytic particles. A combination of transmission electron microscopy, electron energy-loss spectroscopy, and Raman scattering excited with an Ar laser at λ = 514.5 nm (2.41 eV), was used to characterize the nanotubes. The corresponding Raman spectra strongly indicate that these nanotubes are primarily chiral. This method offers a valid route for a high-quality single-step production of SWCNT composites for mechanical, electronic, and optoelectronic applications. © 2002 American Institute of Physics.
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81.07.De Nanotubes
61.46.-w Structure of nanoscale materials
78.67.Ch Nanotubes
78.30.Na Fullerenes and related materials
81.16.Hc Catalytic methods
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.37.Lp Transmission electron microscopy (TEM)
79.20.Uv Electron energy loss spectroscopy
42.70.Mp Nonlinear optical crystals

Studies of phase segregation in Cd1−xZnxTe using surface photovoltage spectroscopy

Y. Zidon, Jihua Yang, and Yoram Shapira

Appl. Phys. Lett. 81, 436 (2002); http://dx.doi.org/10.1063/1.1493230 (3 pages) | Cited 6 times

Online Publication Date: 2 July 2002

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Cd1−xZnxTe wafers used for x-ray detector arrays have been failure analyzed using x-ray diffraction, x-ray electron spectroscopy (XPS), energy dispersive spectroscopy (EDS), and surface photovoltage spectroscopy (SPS). The last shows ZnTe segregation in failed pixels while the precipitant phase is too small to be observed by the other techniques. The Zn concentration, measured using EDS and XPS, was higher than that deduced from SPS data, confirming the conclusion. The segregation can be revealed only by SPS since it is sensitive to the electronic structure and thus to x in each phase while the other techniques average x over their measurement volume. © 2002 American Institute of Physics.
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64.75.-g Phase equilibria
73.25.+i Surface conductivity and carrier phenomena
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Growth of Fe doped semi-insulating GaN by metalorganic chemical vapor deposition

Sten Heikman, Stacia Keller, Steven P. DenBaars, and Umesh K. Mishra

Appl. Phys. Lett. 81, 439 (2002); http://dx.doi.org/10.1063/1.1490396 (3 pages) | Cited 89 times

Online Publication Date: 2 July 2002

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Iron doped GaN layers were grown by metalorganic chemical vapor deposition (MOCVD) using ferrocene as the Fe precursor. Specular films with concentrations up to 1.7×1019 cm−3, as determined by secondary ion mass spectrometry, were grown. The Fe concentration in the film showed a linear dependence on the precursor partial pressure, and was insensitive to growth temperature, pressure, and ammonia partial pressure. Memory effects were observed, similar to Mg doping of GaN by MOCVD. The deep acceptor nature of Fe was used for growth of semi-insulating GaN films on sapphire substrates. A 2.6-μm-thick GaN film with a resistivity of 7×109 Ω/sq was attained when the first 0.3 μm of the film was Fe doped. X-ray diffraction rocking curves indicated high crystalline quality, very similar to an undoped film, showing that Fe doping did not affect the structural properties of the film. Fe doping allows for growth of semi-insulating GaN on sapphire without the high threading dislocation densities and/or high carbon levels that are normally necessary to achieve insulating films. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.S- Impurities in crystals
61.72.up Other materials
73.61.Ey III-V semiconductors
71.55.Eq III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Nephelauxetic effect in LiNbO3:Cr3+ crystals

S. W. Biernacki, A. Kamińska, A. Suchocki, and L. Arizmendi

Appl. Phys. Lett. 81, 442 (2002); http://dx.doi.org/10.1063/1.1493225 (3 pages) | Cited 10 times

Online Publication Date: 2 July 2002

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A model, based on the Harrison theory of bonding is developed for quantitative explanation of the nephelauxetic effect, i.e., a reduction of interelectronic crystal field Racah repulsion parameters B and C due to the covalency of bonds. The results are used for a description of the effect in chromium-doped lithium niobate crystals. The model can be also applied to other systems. © 2002 American Institute of Physics.
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71.70.Ch Crystal and ligand fields
61.50.Lt Crystal binding; cohesive energy

Controlled ice nucleation in microsized water droplet

Du Ning and X. Y. Liu

Appl. Phys. Lett. 81, 445 (2002); http://dx.doi.org/10.1063/1.1492849 (3 pages) | Cited 8 times

Online Publication Date: 2 July 2002

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Controlled ice nucleation in a microsized water droplet was examined using a microdroplet suspension method. This method allows us to minimize the effect of the container wall and foreign particles. The influence of the water droplet volume on microdrop nucleation is examined quantitatively. It is found that at the microscale, the volume effect exerts a large influence on nucleation kinetics. This technique enabled us to quantify the effect of lysozyme on ice nucleation kinetics. It turns out that lysozyme promotes ice nucleation at relatively high supercoolings by decreasing the interfacial free energy between the nucleating phase and foreign particles. This quantitative measurement of the interfacial effect of additives (impurities) on ice nucleation kinetics will exert a significant impact on the research on the mechanism of antifreeze and nucleation promotion. © 2002 American Institute of Physics.
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64.70.D- Solid-liquid transitions
82.70.Kj Emulsions and suspensions
68.08.-p Liquid-solid interfaces

Anomalous x-ray diffraction on InAs/GaAs quantum dot systems

T. U. Schülli, M. Sztucki, V. Chamard, T. H. Metzger, and D. Schuh

Appl. Phys. Lett. 81, 448 (2002); http://dx.doi.org/10.1063/1.1491293 (3 pages) | Cited 12 times

Online Publication Date: 2 July 2002

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Free-standing InAs quantum dots on a GaAs (001) substrate have been investigated using grazing incidence x-ray diffraction. To suppress the strong scattering contribution from the GaAs substrate, we performed anomalous diffraction experiments at the superstructure (200) reflection, showing that the relative intensities from the dots and the substrate undergo a significant change with the x-ray energy below and above the As K edge. Since the signal from the substrate material can essentially be suppressed, this method is ideally suited for the investigation of strain, shape, and interdiffusion of buried quantum dots and quantum dots embedded in heteroepitaxial multilayers. In addition, we show that it can be used as a tool for studying wetting layers. © 2002 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
61.05.cm X-ray reflectometry (surfaces, interfaces, films)

Thermistor ceramic with negative temperature coefficient based on Zn7Sb2O12: An inverse spinel-type phase

M. A. L. Nobre and S. Lanfredi

Appl. Phys. Lett. 81, 451 (2002); http://dx.doi.org/10.1063/1.1494101 (3 pages) | Cited 17 times

Online Publication Date: 2 July 2002

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The electric properties of the semiconductor ceramic Zn7Sb2O12 were investigated by impedance spectroscopy. The grain resistance exhibits a thermistor behavior with negative temperature coefficient. Two regions on the resistance curve were identified. Each region shows a different thermistor characteristic parameter (β), which is equal to 3170 and 3845 °C, at measurement temperatures up to 350 °C and above 450 °C, respectively. The temperature coefficient of the resistance (α) was derived being equal to −2.59×10−2 °C−1 and −1.89×10−2 °C−1, at 350 and 450 °C, respectively. The anomalous behavior of the resistance is further evidence of phase transition phenomenon. © 2002 American Institute of Physics.
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72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Jc Other crystalline inorganic semiconductors
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)

Band gap narrowing of titanium dioxide by sulfur doping

T. Umebayashi, T. Yamaki, H. Itoh, and K. Asai

Appl. Phys. Lett. 81, 454 (2002); http://dx.doi.org/10.1063/1.1493647 (3 pages) | Cited 424 times

Online Publication Date: 2 July 2002

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Titanium dioxide (TiO2) doped with sulfur (S) was synthesized by oxidation annealing of titanium disulfide (TiS2). According to the x-ray diffraction patterns, TiS2 turned into anatase TiO2 when annealed at 600 °C. The residual S atoms occupied O-atom sites in TiO2 to form Ti�S bonds. The S doping caused the absorption edge of TiO2 to be shifted into the lower-energy region. Based on the theoretical analyses using ab initio band calculations, mixing of the S 3p states with the valence band was found to contribute to the band gap narrowing. © 2002 American Institute of Physics.
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71.20.Ps Other inorganic compounds
81.65.Mq Oxidation
81.40.Gh Other heat and thermomechanical treatments
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.15.-m Methods of electronic structure calculations

Intense visible light emission from stress-activated ZrO2:Ti

Morito Akiyama, Chao-Nan Xu, and Kazuhiro Nonaka

Appl. Phys. Lett. 81, 457 (2002); http://dx.doi.org/10.1063/1.1494463 (3 pages) | Cited 16 times

Online Publication Date: 2 July 2002

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We have investigated the luminescence phenomena from stress-activated ZrO2:Ti. The luminescence is clearly visible to the naked eye in the atmosphere. The luminescence center has been identified as the Ti4+ ion from spectra of the mechanoluminescence and also from photoluminescence studies of ZrO2:Ti. The mechanoluminescence intensity decreases on repetitive application of stress but recovers completely on irradiation with ultraviolet light. ZrO2 is an n-type semiconductor and has electron traps. It is suggested that the mechanoluminescence mechanism arises from the movement of dislocations and recombination between electrons and holes released from these traps which are associated with the Ti4+ centers. © 2002 American Institute of Physics.
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78.60.Mq Sonoluminescence, triboluminescence
71.55.Ht Other nonmetals
61.82.Fk Semiconductors
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
78.55.Hx Other solid inorganic materials
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Laser-like mechanoluminescence in ZnMnTe-diluted magnetic semiconductor

D. Raja Reddy and B. K. Reddy

Appl. Phys. Lett. 81, 460 (2002); http://dx.doi.org/10.1063/1.1494116 (3 pages) | Cited 9 times

Online Publication Date: 2 July 2002

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Laser-like mechanoluminescence is reported in the spintronic material ZnMnTe. The luminescence was also observed when the material was exposed to UV and x-rays. Photoluminescence spectra consisted of peaks at 386.5 and 648 nm, which may be attributed to band gap, and Mn2+ levels, respectively. Lattice contraction, sharpness of the x-ray diffraction peak, and the blueshift in the energy gap confirm the nanostructure of the material. A possible mechanism for lasing is also suggested. © 2002 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
78.60.Mq Sonoluminescence, triboluminescence
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors
61.46.-w Structure of nanoscale materials

The anomalous bandgap bowing in GaAsN

U. Tisch, E. Finkman, and J. Salzman

Appl. Phys. Lett. 81, 463 (2002); http://dx.doi.org/10.1063/1.1494469 (3 pages) | Cited 52 times

Online Publication Date: 2 July 2002

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The composition dependence of the fundamental bandgap of thin, pseudomorphic GaAs1−xNx layers (0 ⩽ x ⩽ 5%) on GaAs substrates is studied by optical transmission measurements and high resolution x-ray diffraction. We present a very large set of consistent experimental data. An empirical double exponential composition dependence of the bowing parameter is obtained. This expression accurately describes the measured bandgaps, and allows estimations for higher N incorporations. The bowing parameter reaches 40 eV for very low N incorporations (x ≈ 0.1%), and strongly decreases with increasing N molar fraction. We estimate that the bowing parameter would reach a constant value of 7.5 eV for x≳8%, as in an alloy. This bowing would not be sufficient to close the bandgap for higher N incorporations. © 2002 American Institute of Physics.
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71.20.Nr Semiconductor compounds
78.66.Fd III-V semiconductors
68.55.Nq Composition and phase identification
78.40.Fy Semiconductors
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