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23 Jun 2003

Volume 82, Issue 25, pp. 4411-4611

Issue Cover Spotlight Figure

Appl. Phys. Lett. 82, 4322 (2003); http://dx.doi.org/10.1063/1.1582366 (3 pages)

Hongwei Qu, Wei Yao, T. Garcia, Jiandi Zhang, A. V. Sorokin, S. Ducharme, P. A. Dowben, and V. M. Fridkin
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Atomic-layer-deposited WNxCy thin films as diffusion barrier for copper metallization

Soo-Hyun Kim, Su Suk Oh, Ki-Bum Kim, Dae-Hwan Kang, Wei-Min Li, Suvi Haukka, and Marko Tuominen

Appl. Phys. Lett. 82, 4486 (2003); http://dx.doi.org/10.1063/1.1585111 (3 pages) | Cited 13 times

Online Publication Date: 16 June 2003

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The properties of WNxCy films deposited by atomic layer deposition (ALD) using WF6, NH3, and triethyl boron as source gases were characterized as a diffusion barrier for copper metallization. It is noted that the as-deposited film shows an extremely low resistivity of about 350 μΩ cm with a film density of 15.37 g/cm3. The film composition measured from Rutherford backscattering spectrometry shows W, C, and N of ∼ 48, 32, and 20 at. %, respectively. Transmission electron microscopy analyses show that the as-deposited film is composed of face-centered-cubic phase with a lattice parameter similar to both β-WC1−x and β-W2N with an equiaxed microstructure. The barrier property of this ALD–WNxCy film at a nominal thickness of 12 nm deposited between Cu and Si fails only after annealing at 700 °C for 30 min. © 2003 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.Nq Composition and phase identification
68.55.A- Nucleation and growth
85.40.Ls Metallization, contacts, interconnects; device isolation
68.35.Fx Diffusion; interface formation
61.66.Bi Elemental solids
61.66.Dk Alloys
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
68.37.Lp Transmission electron microscopy (TEM)
81.40.Gh Other heat and thermomechanical treatments

The characteristic carrier–Er interaction distance in Er-doped a-Si/SiO2 superlattices formed by ion sputtering

Ji-Hong Jhe, Jung H. Shin, Kyung Joong Kim, and Dae Won Moon

Appl. Phys. Lett. 82, 4489 (2003); http://dx.doi.org/10.1063/1.1586458 (3 pages) | Cited 42 times

Online Publication Date: 16 June 2003

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The characteristic interaction distance between Er3+ ions and carriers that excite them in Er-doped a-Si/SiO2 superlattices is investigated. Superlattice thin films consisting of 12 periods of a-Si/SiO2:Er/SiO2/SiO2:Er layers were deposited by ion sputtering and subsequent annealing at 950 °C. The dependence of the Er3+ photoluminescence intensity on the thickness of the Er-doped SiO2 layers is well-described by an exponentially decreasing Er-carrier interaction with a characteristic interaction distance of 0.5±0.1 nm. © 2003 American Institute of Physics.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
68.65.Cd Superlattices
78.55.-m Photoluminescence, properties and materials
61.72.Cc Kinetics of defect formation and annealing
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Variable coupling in n-type silicon–germanium double quantum dots

Andrew J. Ferguson, David G. Hasko, H. Ahmed, and David A. Williams

Appl. Phys. Lett. 82, 4492 (2003); http://dx.doi.org/10.1063/1.1577826 (3 pages) | Cited 13 times

Online Publication Date: 16 June 2003

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We report low-temperature electron transport behavior of trench-isolated silicon–germanium (SiGe) double quantum dots. By sweeping the potentials on side gates, we find a hexagonal charging diagram in the conductance measurements. It is also found that the gates allow the parameters of individual tunnel barriers to be changed over a wide range. Charging effects may therefore be observed in different coupling regimes, for example, the two dots that comprise the double dot can be induced to merge together yielding a large single dot. © 2003 American Institute of Physics.
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73.63.Kv Quantum dots

Pyronin B as a donor for n-type doping of organic thin films

A. G. Werner, F. Li, K. Harada, M. Pfeiffer, T. Fritz, and K. Leo

Appl. Phys. Lett. 82, 4495 (2003); http://dx.doi.org/10.1063/1.1583872 (3 pages) | Cited 57 times

Online Publication Date: 16 June 2003

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We present an approach to stable n-type doping of organic matrices using organic dopands. To circumvent stability limitations inherent in strong organic donors, we produce the donor from a stable precursor compound in situ. As an example, pyronin B chloride is studied as a dopant in a 1,4,5,8-naphthalene tetracarboxylic dianhydride matrix. Conductivities up to 2×10−4 S/cm are obtained, which is two orders of magnitude higher than obtained previously using bis(ethylenedithio)-tetrathiafulvalene as a dopant [A. Nollau, M. Pfeiffer, T. Fritz, and K. Leo, J. Appl. Phys. 87, 4340 (2000)]. Field-effect measurements are used to prove n-type conduction. Other matrices which can be doped are N,N′-dimethyl-perylene-3,4,9,10-tetracarboxylic diimide and fullerene C60, frequently used in organic solar cells. Visible light and Fourier-transform infrared spectroscopy confirm the donor properties of pyronin B. © 2003 American Institute of Physics.
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61.72.up Other materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
72.80.Le Polymers; organic compounds (including organic semiconductors)
73.61.Ph Polymers; organic compounds
78.66.Qn Polymers; organic compounds
78.40.Me Organic compounds and polymers
78.30.Jw Organic compounds, polymers

Ballistic electron emission luminescence

Ian Appelbaum, K. J. Russell, V. Narayanamurti, D. J. Monsma, C. M. Marcus, M. P. Hanson, A. C. Gossard, H. Temkin, and C. H. Perry

Appl. Phys. Lett. 82, 4498 (2003); http://dx.doi.org/10.1063/1.1584524 (3 pages) | Cited 14 times

Online Publication Date: 16 June 2003

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We describe the design, fabrication, and operation of a GaAs-based heterostructure device which emits band gap luminescence from solid-state tunnel-junction ballistic injection of electrons with sub-bandgap energy. We find that, due to energy conservation requirements, a collector bias exceeding a threshold determined by the Schottky barrier height and sample band gap energy must be applied for luminescence emission. The consequences of these results for a hybrid scanning-probe microscopy and spectroscopy combining both ballistic electron emission microscopy and scanning tunneling luminescence are emphasized. © 2003 American Institute of Physics.
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07.79.Cz Scanning tunneling microscopes
73.30.+y Surface double layers, Schottky barriers, and work functions
78.60.Fi Electroluminescence
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Exciton and carrier motion in quaternary AlInGaN

K. Kazlauskas, G. Tamulaitis, A. Žukauskas, M. A. Khan, J. W. Yang, J. Zhang, E. Kuokstis, G. Simin, M. S. Shur, and R. Gaska

Appl. Phys. Lett. 82, 4501 (2003); http://dx.doi.org/10.1063/1.1586782 (3 pages) | Cited 15 times

Online Publication Date: 16 June 2003

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Temperature and excitation power dependences of the photoluminescence Stokes shift and bandwidth were studied in quaternary AlInGaN epilayers as a function of indium content. At low excitation power, gradual incorporation of indium into AlGaN is shown to result in S- and W-shaped temperature dependences of the band peak position and bandwidth, respectively. At high excitation power, the S- and W-behavior disappears; however, increased indium molar fraction boosts the redshift of the luminescence band at high temperatures. Our results indicate that the incorporation of indium into AlGaN has a noticeable impact on the alloy transport properties. At low temperatures and low excitation power, the indium incorporation facilitates hopping of localized excitons, whereas at high temperatures and high excitation power, it sustains free motion of delocalized carriers that results in the band-gap renormalization via screening. © 2003 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
71.35.Lk Collective effects (Bose effects, phase space filling, and excitonic phase transitions)
73.50.Dn Low-field transport and mobility; piezoresistance

Effect of surface treatment on leakage current of GaAs/AlGaAs laser microcavities

Jun-Youn Kim, Jawoong Lee, Jungyeon Kim, Bongkoo Kang, and O’Dae Kwon

Appl. Phys. Lett. 82, 4504 (2003); http://dx.doi.org/10.1063/1.1584784 (3 pages) | Cited 6 times

Online Publication Date: 16 June 2003

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The effect of surface treatment on leakage current is investigated for two structures of the electropumped GaAs/AlGaAs laser microcavities, one with mesa and the other with hyperboloid-drum structures. Using surface sheet resistivity as a figure-of-merit parameter, the results of different surface treatment methods are compared. The best result is obtained when the sample has been polished in a H2SO4:H2O2:H2O = 1:8:1000 solution for 5 s, and treated subsequently in a 6% excess sulfur-containing (NH4)2Sx solution at 60 °C for 8 mins. The treatment in (NH4)2Sx solution increases the surface sheet resistivity by a factor of ∼14. The cross-sectional shape of the cavity and the vertical profile of distributed Bragg reflector mirrors have little correlation with the leakage current. © 2003 American Institute of Physics.
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42.55.Sa Microcavity and microdisk lasers
81.05.Ea III-V semiconductors
81.65.Ps Polishing, grinding, surface finishing
73.25.+i Surface conductivity and carrier phenomena
68.47.Fg Semiconductor surfaces
42.86.+b Optical workshop techniques
68.35.B- Structure of clean surfaces (and surface reconstruction)
42.79.Bh Lenses, prisms and mirrors

High tunnel magnetoresistance in epitaxial Fe/MgO/Fe tunnel junctions

J. Faure-Vincent, C. Tiusan, E. Jouguelet, F. Canet, M. Sajieddine, C. Bellouard, E. Popova, M. Hehn, F. Montaigne, and A. Schuhl

Appl. Phys. Lett. 82, 4507 (2003); http://dx.doi.org/10.1063/1.1586785 (3 pages) | Cited 85 times

Online Publication Date: 16 June 2003

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We report on spin-polarized tunneling in fully epitaxial Fe/MgO/Fe/Co tunnel junctions. By increasing the thickness of the insulating layer (tMgO), we have strongly enhanced the tunnel magnetoresistance. Values up to ∼100% at 80 K (∼67% at room temperature) have been observed with tMgO = 2.5 nm. This tunnel magnetoresistance ratio, which is much larger than the one predicted by the Jullière’s model, can be understood in the framework of ab initio calculations. © 2003 American Institute of Physics.
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85.75.Mm Spin polarized resonant tunnel junctions
75.50.Bb Fe and its alloys

Physical explanation of the barrier height temperature dependence in metal-oxide-semiconductor leakage current models

Dietmar Schroeder and Alejandro Avellán

Appl. Phys. Lett. 82, 4510 (2003); http://dx.doi.org/10.1063/1.1587256 (3 pages) | Cited 2 times

Online Publication Date: 16 June 2003

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A temperature dependence of the barrier height between silicon and oxide has been proposed by many authors in order to reflect experimental metal-oxide-semiconductor leakage current results. However, no satisfactory physical explanation of this dependence has yet been given. In this letter, the temperature dependence of the observed macroscopic barrier height is explained by thermal fluctuations of the microscopic local barrier height. Because of the exponential relationship between current and barrier height, the decrease of the barrier during the fluctuation has a dominating effect when compared to the increase, leading on the average to a raised leakage current and correspondingly to a lowered average barrier height. © 2003 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
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Magnetic property enhancement of melt-spun Pr2Fe23B3 ribbons with dilute Ti substitution

H. W. Chang, C. H. Chiu, and W. C. Chang

Appl. Phys. Lett. 82, 4513 (2003); http://dx.doi.org/10.1063/1.1584787 (3 pages) | Cited 25 times

Online Publication Date: 16 June 2003

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The phase evolution and magnetic properties of Pr2Fe23B3 and Pr2(Fe0.975Ti0.025)23B3 melt-spun ribbons have been investigated. For Pr2Fe23B3 spun at 25 m/s, the magnetically hard Pr2Fe14B phase coexists with α-Fe, Pr2Fe23B3, and Fe3B when annealed at temperatures above 700 °C, while merely two phases, namely, Pr2Fe14B and α-Fe, coexist if annealed above 800 °C. Because of the excessive annealing, these ribbons exhibit large grain sizes that lead to low Br and iHc values. A slight substitution of Ti for Fe in Pr2(Fe0.975Ti0.025)23B3 suppresses the formation of metastable Pr2Fe23B3 phase and leads to the presence of large amount of Pr2Fe14B and α-Fe phases of fine grain sizes in the matrix even at low annealing temperature (i.e., TH = 650 °C). As a result, the magnetic properties improve remarkably from Br = 6.7 kG, iHc = 1.5 kOe and (BH)max = 1.7 MG Oe of the ternary Pr2Fe23B3 to Br = 9.9 kG, iHc = 5.7 kOe and (BH)max = 15.0 MGOe of the Pr2(Fe0.975Ti0.025)23B3. © 2003 American Institute of Physics.
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81.40.Rs Electrical and magnetic properties related to treatment conditions
75.50.Bb Fe and its alloys
75.50.Ww Permanent magnets
81.40.Gh Other heat and thermomechanical treatments
81.20.-n Methods of materials synthesis and materials processing
61.66.Bi Elemental solids
61.66.Dk Alloys

Laser threshold reduction in a spintronic device

J. Rudolph, D. Hägele, H. M. Gibbs, G. Khitrova, and M. Oestreich

Appl. Phys. Lett. 82, 4516 (2003); http://dx.doi.org/10.1063/1.1583145 (3 pages) | Cited 38 times

Online Publication Date: 16 June 2003

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We demonstrate a reduction of the threshold of a semiconductor laser by optically pumping spin-polarized electrons in the gain medium. Polarized electrons couple selectively to one of two possible lasing light modes which effectively reduces the threshold by up to 50% compared to conventional pumping with unpolarized electrons. We theoretically show that our concept can be generalized to an electrically pumped laser. © 2003 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes

Strongly coupled critical current density values achieved in Y1Ba2Cu3O7−δ coated conductors with near-single-crystal texture

S. R. Foltyn, P. N. Arendt, Q. X. Jia, H. Wang, J. L. MacManus-Driscoll, S. Kreiskott, R. F. DePaula, L. Stan, J. R. Groves, and P. C. Dowden

Appl. Phys. Lett. 82, 4519 (2003); http://dx.doi.org/10.1063/1.1584783 (3 pages) | Cited 66 times

Online Publication Date: 16 June 2003

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One of the most intensely researched subjects in the development of YBa2Cu3O7−δ (YBCO)-based coated conductors is the methodology for achieving ever-sharper film texture on flexible metal substrates. This is a critical issue due to the intrinsic weak-link behavior that results in depressed critical current density (Jc) in polycrystalline YBCO. Using ion-beam-assisted deposition of magnesium oxide, we have achieved YBCO texture on superalloy substrates approaching that on single-crystal oxide substrates. This advance has allowed us to fabricate coated conductor samples with Jcs that are as high as for films on oxide crystals; for example, >2 MA/cm2 (75 K, self-field) at a YBCO thickness of ∼1.5 μm. © 2003 American Institute of Physics.
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74.25.Sv Critical currents
74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures

Conducting atomic-force-microscope electrical characterization of submicron magnetic tunnel junctions

D. C. Worledge and David W. Abraham

Appl. Phys. Lett. 82, 4522 (2003); http://dx.doi.org/10.1063/1.1582375 (3 pages) | Cited 21 times

Online Publication Date: 16 June 2003

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We have developed the ability to electrically characterize submicron magnetic tunnel junctions using a conducting atomic force microscope (CAFM). This technique can be applied after only a short processing route, thereby saving time and resources, and reducing the potential for damaging the junctions. The CAFM can be used to measure hysteresis loops, magnetoresistance, resistance–area product, switching astroids, current–voltage curves, and breakdown voltage of tunnel junctions. In this letter, we outline the sample requirements, detail the CAFM processing route, describe tip preparation, and report examples of data we have obtained with this technique over the last two years. © 2003 American Institute of Physics.
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72.25.Mk Spin transport through interfaces
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.37.Ps Atomic force microscopy (AFM)
68.35.Ct Interface structure and roughness
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Microwave intermodulation distortion of MgB2 thin films

G. Lamura, A. J. Purnell, L. F. Cohen, A. Andreone, F. Chiarella, E. Di Gennaro, R. Vaglio, L. Hao, and J. Gallop

Appl. Phys. Lett. 82, 4525 (2003); http://dx.doi.org/10.1063/1.1584519 (3 pages) | Cited 12 times

Online Publication Date: 16 June 2003

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The two-tone intermodulation arising in MgB2 thin films deposited in situ by planar magnetron sputtering on sapphire substrates is studied. Samples are characterized using an open-ended dielectric puck resonator operating at 8.8 GHz. The experimental results show that the third-order products increase with the two-tone input power with a slope ranging between 1.5 and 2.3. The behavior can be understood introducing a mechanism of vortex penetration in grain boundaries as the most plausible source of nonlinearities in these films. This assumption is confirmed by the analysis of the field dependence of the surface resistance, that show a linear behavior at all temperatures under test. © 2003 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
73.25.+i Surface conductivity and carrier phenomena
74.25.N- Response to electromagnetic fields
72.30.+q High-frequency effects; plasma effects
74.25.F- Transport properties
61.72.Mm Grain and twin boundaries

High-resolution detection of resonant frequencies of microwave resonators via magnetic measurements

R. Amigó, J. M. Hernandez, A. García-Santiago, and J. Tejada

Appl. Phys. Lett. 82, 4528 (2003); http://dx.doi.org/10.1063/1.1586786 (3 pages) | Cited 5 times

Online Publication Date: 16 June 2003

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An experiment with high spin molecular magnets inside microwave resonators has produced the remarkable observation of sharp peaks in the equilibrium magnetization and the ac susceptibility for the resonant frequencies of these devices. These peaks appear when the magnets are pumped or warmed by microwaves to states of different magnetic moment, and allow one to carry out spectroscopic studies of either the magnetic materials or the resonant device. © 2003 American Institute of Physics.
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07.55.-w Magnetic instruments and components
75.50.Xx Molecular magnets
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
84.40.-x Radiowave and microwave (including millimeter wave) technology

Strain-induced charge depletion in La2/3Ca1/3MnO3 epitaxial thin films

S. Valencia, Ll Balcells, J. Fontcuberta, and B. Martínez

Appl. Phys. Lett. 82, 4531 (2003); http://dx.doi.org/10.1063/1.1587000 (3 pages) | Cited 23 times

Online Publication Date: 16 June 2003

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Epitaxial thin films of La2/3Ca1/3MnO3 (LCMO), 50 nm thick, have been grown fully strained, on SrTiO3 (001) substrates. Detailed analyses of the structural and magnetotransport properties, after high-temperature annealing processes, have revealed a progressive increase of the out-of-plane cell parameter c, as the annealing temperature rises but no changes in the in-plane cell parameters are observed. Simultaneously, the magnetic transition temperature, TC, and saturation magnetization, MS, substantially increase. We argue that these results can be described assuming that elastic energy in fully strained films could be minimized by introducing oxygen deficiencies in the as-grown films. This observation provides a simple understanding of the commonly observed depressed magnetotransport properties of LCMO grown on nonmatching substrates. © 2003 American Institute of Physics.
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75.47.Lx Magnetic oxides
68.60.Bs Mechanical and acoustical properties
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
68.55.-a Thin film structure and morphology
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Structural and magnetic properties of triode-sputtered epitaxial γ′-Fe4N films deposited on SrTiO3 (001) substrates

K. R. Nikolaev, I. N. Krivorotov, E. D. Dahlberg, V. A. Vas’ko, S. Urazhdin, R. Loloee, and W. P. Pratt

Appl. Phys. Lett. 82, 4534 (2003); http://dx.doi.org/10.1063/1.1586790 (3 pages) | Cited 12 times

Online Publication Date: 16 June 2003

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Highly ordered, single-crystal Fe4N films were prepared on single-crystal SrTiO3 (001) substrates by reactive magnetically enhanced dc triode sputtering. Analytical techniques, including x-ray diffraction, reflectivity, ion channeling, and atomic force microscopy, were used to characterize the structure and morphology of the films. The magnetic properties of the films were measured by magnetic force microscopy and superconducting quantum interference device magnetometry. A technique that utilizes anisotropic magnetoresistance was employed for measurement of the magnetocrystalline anisotropy of the Fe4N films. © 2003 American Institute of Physics.
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75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
68.55.-a Thin film structure and morphology
75.30.Gw Magnetic anisotropy
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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Ba8ZnTa6O24: a high-Q microwave dielectric from a potentially diverse homologous series

S. M. Moussa, J. B. Claridge, M. J. Rosseinsky, S. Clarke, R. M. Ibberson, T. Price, D. M. Iddles, and D. C. Sinclair

Appl. Phys. Lett. 82, 4537 (2003); http://dx.doi.org/10.1063/1.1582363 (3 pages) | Cited 24 times

Online Publication Date: 16 June 2003

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The ceramic Ba8ZnTa6O24 has been synthesized in isolation and its dielectric and crystallographic properties characterized. The material affords excellent dielectric properties, with a high unloaded quality factor Qu = 20 800 at 3.28 GHz, high relative permittivity εr = 29 and a temperature coefficient of resonant frequency τf = 29.4 ppm/°C. The crystal structure adopted is complex, comprising mixed cubic and hexagonal perovskite subunits, and contains cation vacancies on the octahedral sites. A second phase with a closely related structure is identified, demonstrating the existence of a family of materials. This structural complexity offers diverse opportunities for substitutions calculated to enhance the figures of merit reported. © 2003 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.-e Ferroelectricity and antiferroelectricity
61.66.Fn Inorganic compounds
77.22.Ch Permittivity (dielectric function)

Residual stress analysis in ferroelectric Pb(Zr0.52Ti0.48)O3 thin films fabricated by a sol-gel process

Kui Yao, Shuhui Yu, and Francis Eng-Hock Tay

Appl. Phys. Lett. 82, 4540 (2003); http://dx.doi.org/10.1063/1.1587272 (3 pages) | Cited 25 times

Online Publication Date: 16 June 2003

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Ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) films were prepared by a modified sol-gel process, in which polyethylene glycol (PEG) was added to the precursor solutions. An x-ray diffraction (XRD) method that detected the d(123) variation associated with the change in the incline angle ψ of the plane (123) was developed to quantify the residual stress in the PZT films. The stress could not be determined from the wafer curvature due to the effects of both the underlying layers and interdiffusion among layers. Using our XRD method, it was found that the residual stress in the resulting PZT films was significantly reduced when PEG was added to the precursor solutions. Moreover, we observed a further reduction of residual stress with increasing molecular weight of the PEG additive. These results could explain why a thicker, crack-free film can be achieved by adding polymers to the sol-gel precursor solutions. © 2003 American Institute of Physics.
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81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
77.80.-e Ferroelectricity and antiferroelectricity
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Voltage-induced phase transition in arrays of metallic nanodots: Computed transport and surface potential structure

F. Remacle and R. D. Levine

Appl. Phys. Lett. 82, 4543 (2003); http://dx.doi.org/10.1063/1.1583871 (3 pages) | Cited 3 times

Online Publication Date: 16 June 2003

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Computed dc transport in compressed arrays of metallic quantum dots exhibits a voltage-induced phase transition at low temperatures. The transition is seen in the temperature dependence of the conductance at different voltages: from a variable hopping dependence at low voltage to an ohmic, activated behavior at higher voltages. The computations also exhibit the transition as a break in the current versus voltage plots at low temperatures where, at higher voltages, the plot is linear. At higher temperatures, the conductance is ohmic. A many-electron basis is used. The same transition is seen in the surface potential contours. © 2003 American Institute of Physics.
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73.63.Kv Quantum dots
71.30.+h Metal-insulator transitions and other electronic transitions

White light source in infrared region from InAs quantum dots grown on (001) InP substrates by droplet heteroepitaxy

R. Oga, W. S. Lee, Y. Fujiwara, and Y. Takeda

Appl. Phys. Lett. 82, 4546 (2003); http://dx.doi.org/10.1063/1.1585138 (3 pages) | Cited 3 times

Online Publication Date: 16 June 2003

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We have observed extremely wide spectral range electroluminescence (EL) from InAs quantum dots (QDs) on (001) InP substrates at room temperature. The InAs QDs were grown by droplet heteroepitaxy using a low-pressure organometallic vapor phase epitaxial system. Room-temperature EL in a very wide wavelength range from 950 to 2200 nm was observed from InAs QDs embedded in InP matrix. The wide range emission indicates that the QDs have white optical gain in the infrared region at room temperature, which can be applied to efficient optical amplifiers for 1.0–1.6 μm fiber communication. © 2003 American Institute of Physics.
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78.67.Hc Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
73.21.La Quantum dots
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.72.Bj Visible and ultraviolet sources
78.60.Fi Electroluminescence
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.55.Wd Fiber lasers
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Surface pattern evolution during thermal Cl2 etching of GaAs(001)

J. H. Schmid, R. Mar, and T. Tiedje

Appl. Phys. Lett. 82, 4549 (2003); http://dx.doi.org/10.1063/1.1584091 (3 pages) | Cited 1 time

Online Publication Date: 16 June 2003

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The evolution of one- and two-dimensional surface gratings during maskless thermal Cl2 etching of GaAs is investigated using atomic force microscopy. It is found that the limiting factor for pattern transfer is the anisotropy of the etch rate with respect to crystal orientation. A simple numerical model based on an interpolation of measured etch rates is presented that can be used to calculate the evolution of surface patterns. © 2003 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning

Direct measurement of polarization resolved transition dipole moment in InGaAs/GaAs quantum dots

K. L. Silverman, R. P. Mirin, S. T. Cundiff, and A. G. Norman

Appl. Phys. Lett. 82, 4552 (2003); http://dx.doi.org/10.1063/1.1584514 (3 pages) | Cited 26 times

Online Publication Date: 16 June 2003

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The propagation of optical pulses resonant with the ground-to-excited state transition of InGaAs quantum dots is investigated. An analysis of low intensity excitation yields a dipole moment of 8.8×10−29 to 10.9×10−29 C m, depending on the quantum dot growth conditions. We observe polarization of the dipole moment exclusively in the plane perpendicular to the growth direction. © 2003 American Institute of Physics.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
73.21.La Quantum dots
81.07.Ta Quantum dots
68.37.Lp Transmission electron microscopy (TEM)

Surface morphology control of InAs nanostructures grown on InGaAs/InP

Z. H. Zhang, G. W. Pickrell, K. L. Chang, H. C. Lin, K. C. Hsieh, and K. Y. Cheng

Appl. Phys. Lett. 82, 4555 (2003); http://dx.doi.org/10.1063/1.1584523 (3 pages) | Cited 15 times

Online Publication Date: 16 June 2003

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The evolution of the surface morphology of InAs nanostructures grown on InGaAs/InP by molecular-beam epitaxy was studied through atomic force microscopy imaging. Randomly distributed quantum dots and quantum wires were reproducibly achieved by adjusting proper growth parameters such as InAs deposition thickness, growth temperature, arsenic overpressure, and InAs growth rate. It is observed that a thick InAs layer, high growth temperature, high arsenic overpressure, and high growth rate promote the formation of quantum dots. We propose that when InAs is deposited, the interaction of the total strain in the InAs layer and the surface strain distribution in the underlying matrix layer might be the determinant factor of the nanostructure morphology. Thick InAs, which increases the total strain of the InAs layer, is preferred to form quantum dots. Surface diffusion of In adatoms is another important factor affecting the surface morphology. A high growth temperature promotes homogeneous diffusion, while a high arsenic overpressure and growth rate reduces the surface diffusion of the In adatoms. These factors induce the formation of quantum dots. © 2003 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.65.La Quantum wires (patterned in quantum wells)
68.65.Hb Quantum dots (patterned in quantum wells)
81.05.Ea III-V semiconductors
68.47.Fg Semiconductor surfaces
81.07.Ta Quantum dots
81.07.Vb Quantum wires
61.46.-w Structure of nanoscale materials
68.37.Ps Atomic force microscopy (AFM)
68.35.Fx Diffusion; interface formation
68.43.Jk Diffusion of adsorbates, kinetics of coarsening and aggregation
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.Gy Mechanical properties; surface strains

Time-delayed indium incorporation in ultrathin (InxGa1−xN/GaN) multiple quantum wells grown by metalorganic vapor phase epitaxy

F. Schulze, J. Bläsing, A. Dadgar, and A. Krost

Appl. Phys. Lett. 82, 4558 (2003); http://dx.doi.org/10.1063/1.1586472 (3 pages) | Cited 7 times

Online Publication Date: 16 June 2003

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InxGa1−xN/GaN multiple quantum wells grown by metalorganic vapor phase epitaxy were investigated by x-ray reflectometry and high-resolution x-ray diffractometry. The combination of both analysis methods allows a very precise determination of the structural parameters of the layer systems. From a systematic variation of the growth temperature from 760 to 840 °C and deposition times from 15 to 200 s, a temperature-dependent time delay of the indium incorporation was observed. Preferentially, at lower growth temperatures, indium seems to be accumulated at the GaN surface before the onset of the InGaN quantum well growth. The growth delay increases with decreasing growth temperature. © 2003 American Institute of Physics.
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81.05.Ea III-V semiconductors
68.65.Fg Quantum wells
81.07.St Quantum wells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
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