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25 Feb 2008

Volume 92, Issue 8, Articles (08xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 92, 081101 (2008); http://dx.doi.org/10.1063/1.2883874 (3 pages)

Marcel W. Pruessner, Todd H. Stievater, and William S. Rabinovich
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Nonlinear relaxation of zero-dimension-trapped microcavity polaritons

Ounsi El Daif, Gaël Nardin, Taofiq K. Paraïso, Augustin Baas, Maxime Richard, J.-P. Brantut, Thierry Guillet, Francois Morier-Genoud, and Benoit Deveaud-Plédran

Appl. Phys. Lett. 92, 081910 (2008); http://dx.doi.org/10.1063/1.2885018 (3 pages) | Cited 5 times

Online Publication Date: 26 February 2008

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We study the emission properties of confined polariton states in shallow zero-dimensional traps under nonresonant excitation. We evidence several relaxation regimes. For slightly negative photon-exciton detuning, we observe a nonlinear increase of the emission intensity, characteristic of carrier-carrier scattering assisted relaxation under strong-coupling regime. This demonstrates the efficient relaxation toward a confined state of the system. For slightly positive detuning, we observe the transition from strong to weak coupling regime and then to single-mode lasing.
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71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
71.35.-y Excitons and related phenomena
78.55.Cr III-V semiconductors

Impact of annealing on morphology and ferromagnetism of ZnO nanorods

Zijie Yan, Yanwei Ma, Dongliang Wang, Junhong Wang, Zhaoshun Gao, Lei Wang, Peng Yu, and Tao Song

Appl. Phys. Lett. 92, 081911 (2008); http://dx.doi.org/10.1063/1.2887906 (3 pages) | Cited 30 times

Online Publication Date: 27 February 2008

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Room temperature ferromagnetism has been observed in ZnO nanorods prepared by hydrothermal method. Saturation magnetization of ∼ 0.004 emu/g was measured in the nanorods with diameters of ∼ 10 nm and lengths of below 100 nm, and the magnetization reduced with the increase of the size. Annealing of the samples at 900 °C in air completely transformed the nanorods into twinning structures and weakened the magnetizations. The mechanism of morphology transformation was discussed. Analysis indicates that the interstitial zinc at the surface may contribute to the ferromagnetism in ZnO nanorods.
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75.75.-c Magnetic properties of nanostructures
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Nt Magnetic annealing and temperature-hysteresis effects
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)

Measuring the interface stress of nanocrystalline iron

Patrik Zimmer and Rainer Birringer

Appl. Phys. Lett. 92, 081912 (2008); http://dx.doi.org/10.1063/1.2888751 (3 pages) | Cited 5 times

Online Publication Date: 27 February 2008

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With the ongoing miniaturization of structures and devices down to the nanometer scale, we notice concomitant escalation of atoms located at surfaces or interfaces. Presence of surfaces and interfaces generates stresses in nanoscale structures that can easily exceed 1 GPa. We developed and applied a method for measuring the absolute value of grain-boundary stress. Since investigation of grain-boundary stress as well as phase-boundary stress of body-centered-cubic materials has not been addressed so far, we aimed at determining the grain-boundary stress f of nanocrystalline Fe. By means of x-ray diffraction measurements of average grain size and residual-strain-free lattice spacings, we deduced a value of f = 1.1±0.2 N/m.
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61.46.Hk Nanocrystals
61.72.Mm Grain and twin boundaries
68.35.Gy Mechanical properties; surface strains

Highly coherent thermal emission obtained by plasmonic bandgap structures

Gabriel Biener, Nir Dahan, Avi Niv, Vladimir Kleiner, and Erez Hasman

Appl. Phys. Lett. 92, 081913 (2008); http://dx.doi.org/10.1063/1.2883948 (3 pages) | Cited 10 times

Online Publication Date: 27 February 2008

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We demonstrate an extraordinary quasimonochromatic thermal emission with high spatial coherence length (lc>2400λ) and a quality factor Q = 2320 at radiation frequencies that are much smaller than the plasma frequency of metal (ω≪ωp). This emission is achieved by forming a plasmonic bandgap, which is obtained by a periodic structure on a metallic surface. Such a structure modifies the dynamics of the surface wave and results in a van Hove singularity [ Van Hove, Phys. Rev. 89, 1189 (1953) ] in the spectral density of states while maintaining a large coherence length.
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79.40.+z Thermionic emission
78.68.+m Optical properties of surfaces
42.72.Ai Infrared sources
42.25.Kb Coherence

Nanograin nucleation initiated by intergrain sliding and/or lattice slip in nanomaterials

S. V. Bobylev and I. A. Ovid’ko

Appl. Phys. Lett. 92, 081914 (2008); http://dx.doi.org/10.1063/1.2885069 (3 pages) | Cited 6 times

Online Publication Date: 27 February 2008

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Stress-induced nucleation of nanoscale grains (nanograins) in deformed nanocrystalline metals and ceramics is theoretically described as a process initiated by intergrain sliding and/or lattice slip. The nanograin nucleation occurs through splitting and migration of grain boundaries containing disclination dipoles produced by intergrain sliding and/or lattice slip. It is shown that the nanograin nucleation is energetically favorable in mechanically loaded nanocrystalline Al and α-Al2O3 in certain ranges of their parameters and the external stress level.
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61.72.Mm Grain and twin boundaries
66.30.-h Diffusion in solids
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
61.72.Bb Theories and models of crystal defects

Phosphorescence characteristics of ruthenium complex as an optical transducer for biosensors

Sean B. Pieper, Santano P. Mestas, Kevin L. Lear, Zhong Zhong, and Kenneth F. Reardon

Appl. Phys. Lett. 92, 081915 (2008); http://dx.doi.org/10.1063/1.2885082 (3 pages) | Cited 4 times

Online Publication Date: 27 February 2008

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The saturation intensity, photobleaching, and decay lifetime of tris(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) chloride [Ru(dpp)3] are investigated. The saturation point was estimated to be 11.8 W/cm2 and subsequently measured to be 11.5 W/cm2. Photobleaching of this dye at a peak absorbance equivalence of 6.6 W/cm2 is observed over 2 days resulting in a 14% decrease in intensity within 20 min and 47% decrease over two days yielding an unacceptably short operational lifetime under saturated conditions. Lower optical excitation levels in the application of oxygen sensitive fluorescence type fiber optic enzymatic biosensor systems are required and yield acceptable photobleaching rates.
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87.85.fk Biosensors
42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption
42.81.Pa Sensors, gyros
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A mechanism for dynamic lateral polarization in CdZnTe under high flux x-ray irradiation

Derek S. Bale, Stephen A. Soldner, and Csaba Szeles

Appl. Phys. Lett. 92, 082101 (2008); http://dx.doi.org/10.1063/1.2883924 (3 pages) | Cited 7 times

Online Publication Date: 25 February 2008

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It has been observed that pixillated CdZnTe detectors fabricated from crystals with low hole transport properties (μhτh<10−5 cm2 V−1) experience a dynamic lateral polarization when exposed to a high flux of x-rays. In this effect, counts are transferred from pixels near the edge of the irradiated region to pixels in the interior. In this letter, we propose a mechanism capable of explaining the observed dynamical effect. The mechanism is based on a transverse electric field that is generated due to space charge that builds within the material. This transverse field, in turn, is responsible for the altered carrier trajectories toward the center of the irradiated region.
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29.40.Wk Solid-state detectors
61.80.Cb X-ray effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
29.40.Gx Tracking and position-sensitive detectors
72.20.Fr Low-field transport and mobility; piezoresistance

Spectroscopic study of microwave-enhanced silicon exfoliation

D. C. Thompson, T. L. Alford, and J. W. Mayer

Appl. Phys. Lett. 92, 082102 (2008); http://dx.doi.org/10.1063/1.2842420 (3 pages) | Cited 2 times

Online Publication Date: 25 February 2008

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Infrared spectroscopy and Rutherford backscattering spectrometry are used to study the effect of microwaves on hydrogen implanted silicon. Infrared spectra demonstrate that the hydride species formed in hydrogen implant and microwave annealed silicon result in exfoliation in a manner similar to that in conductively annealed samples. The infrared spectra of microwave annealed samples reveal an increase in internal surface formation prior to exfoliation. This increase in internal surface formation demonstrates how microwave anneals can decrease the incubation time required prior to exfoliation. Rutherford backscattering and infrared spectra are presented to elucidate the minimized impact of the microwave effect in boron-hydrogen coimplanted silicon.
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78.30.-j Infrared and Raman spectra
61.72.U- Doping and impurity implantation
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Differential conductance fluctuations in silicon nanowire transistors caused by quasiballistic transport and scattering induced intersubband transitions

Seonghoon Jin, Massimo V. Fischetti, and Ting-wei Tang

Appl. Phys. Lett. 92, 082103 (2008); http://dx.doi.org/10.1063/1.2888963 (3 pages) | Cited 7 times

Online Publication Date: 26 February 2008

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Calculations based on the multisubband Boltzmann transport equation with relevant microscopic scattering mechanisms predict abrupt differential conductance fluctuations (kinks) in the drain current versus drain voltage curves of silicon nanowire transistors at room temperature. The kink originates from the change of series resistance at the drain extension related to the interplay between quasiballistic transport and intersubband transitions of electrons caused by elastic interactions with acoustic phonons, surface roughness, and ionized impurities. The kink occurs when the energy of the second subband in the drain extension is aligned with the peak of the net electron flux distribution in the first subband. This bias condition yields a large series resistance in the drain extension because those quasiballistic electrons in the first subband which reach the drain can scatter isotropically into the second subband.
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85.30.Tv Field effect devices
73.23.Ad Ballistic transport
68.35.B- Structure of clean surfaces (and surface reconstruction)
62.65.+k Acoustical properties of solids

Signal and charge transfer efficiency of few electrons clocked on microscopic superfluid helium channels

G. Sabouret, F. R. Bradbury, S. Shankar, J. A. Bert, and S. A. Lyon

Appl. Phys. Lett. 92, 082104 (2008); http://dx.doi.org/10.1063/1.2884693 (3 pages) | Cited 4 times

Online Publication Date: 26 February 2008

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Electrons floating on the surface of liquid helium are possible spin qubits for quantum information processing. Varying electric potentials are not expected to modify spin states, which allows their transport on helium using a charge-coupled device (CCD)-like array of underlying gates. This approach depends upon efficient intergate transfer of individual electrons. Measurements are presented here of the charge transfer efficiency of few electrons clocked back and forth above a short microscopic CCD-like structure. A charge transfer efficiency of 0.999 999 92 is obtained for a clocking frequency of 800 kHz.
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67.25.dg Transport, hydrodynamics, and superflow
03.67.Lx Quantum computation architectures and implementations

Persistent photoconductivity and carrier transport in AlGaN/GaN heterostructures treated by fluorine plasma

B. K. Li, W. K. Ge, J. N. Wang, and K. J. Chen

Appl. Phys. Lett. 92, 082105 (2008); http://dx.doi.org/10.1063/1.2888743 (3 pages) | Cited 9 times

Online Publication Date: 27 February 2008

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Fluorine plasma treatment technique can effectively incorporate fluorine atoms into the AlGaN barrier, depleting the two-dimensional electron gases (2DEGs) in the channel of AlGaN/GaN high electron mobility transistors and converting the device from depletion mode to enhancement mode. To reveal the underlying physical mechanisms, temperature dependent persistent photoconductivity (PPC) and Hall measurements are conducted in AlGaN/GaN heterostructures treated by CF4 plasma. Weakly temperature dependent 2DEG mobility and much more pronounced PPC effect are observed in the F-treated sample. An energy barrier of 624 meV for electrons recaptured by the F-related centers is extracted from the PPC decay behaviors.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.40.+w Photoconduction and photovoltaic effects
52.77.-j Plasma applications
72.20.My Galvanomagnetic and other magnetotransport effects

Effects of interface states on the transport properties of all-oxide La0.8Sr0.2CoO3/SrTi0.99Nb0.01O3 p-n heterojunctions

F. Y. Bruno, J. Garcia-Barriocanal, M. Torija, A. Rivera, Z. Sefrioui, C. Leighton, C. Leon, and J. Santamaria

Appl. Phys. Lett. 92, 082106 (2008); http://dx.doi.org/10.1063/1.2887905 (3 pages) | Cited 10 times

Online Publication Date: 28 February 2008

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Electrical transport properties of heteroepitaxial p-n junctions made of La0.8Sr0.2CoO3 and SrTi0.99Nb0.01O3 were studied. Junctions display highly rectifying current-voltage characteristics over a wide temperature range (20–300 K). Two distinct transport mechanisms are identified: tunneling assisted by interface states at T<130 K and diffusion/recombination at higher temperatures. Capacitance-voltage characteristics are used to determine the junction built-in potential at different frequencies. A capacitance relaxation is found due to charge trapping at interface states. Interface states, which deeply affect transport, are discussed in connection to charge-transfer processes related to the polarity mismatch at the interface.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.20.At Surface states, band structure, electron density of states
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Jc Other crystalline inorganic semiconductors
73.40.Gk Tunneling

Arsenic δ-doped HgTe/HgCdTe superlattices grown by molecular beam epitaxy

G. K. O. Tsen, C. A. Musca, J. M. Dell, J. Antoszewski, L. Faraone, and C. R. Becker

Appl. Phys. Lett. 92, 082107 (2008); http://dx.doi.org/10.1063/1.2888967 (3 pages) | Cited 5 times

Online Publication Date: 28 February 2008

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Arsenic incorporation in HgTe/Hg0.05Cd0.95Te superlattices grown by molecular beam epitaxy (MBE) is reported. The incorporation was carried out by a δ-doping approach where arsenic was incorporated during MBE growth as acceptors. The superlattices were characterized via high resolution x-ray diffraction, Fourier transform infrared spectroscopy, secondary ion mass spectrometry, and magnetotransport Hall measurements coupled with the quantitative mobility spectrum analysis algorithm.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.65.Cd Superlattices
61.72.uj III-V and II-VI semiconductors
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.30.Fs III-V and II-VI semiconductors
73.63.-b Electronic transport in nanoscale materials and structures

Interfacial reactions of Pt-based Schottky contacts on InGaP

L. H. Chu, E. Y. Chang, Y. H. Wu, J. C. Huang, Q. Y. Chen, W. K. Chu, H. W. Seo, and C. T. Lee

Appl. Phys. Lett. 92, 082108 (2008); http://dx.doi.org/10.1063/1.2834849 (3 pages)

Online Publication Date: 28 February 2008

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We have investigated the interfacial reaction between platinum and InGaP in a Schottky diode structure. There was a 7.5-nm-thick amorphous layer formed at the interface between Pt and InGaP after metal deposition. After annealing at 325 °C for 1 min, this amorphous layer increased to 12.8 nm and the reverse leakage current also decreased. The diffusion of Pt atoms and the crystallization of amorphous layer took place after annealing at 325 °C for 10 min. Prolonging the annealing to 3 h led to formation of Ga2Pt and GaPt3 phases in InGaP and Schottky diodes degraded after these new phases were observed.
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
66.30.Ny Chemical interdiffusion; diffusion barriers
81.40.Gh Other heat and thermomechanical treatments
64.70.kg Semiconductors

Surface proximity and boron concentration effects on end-of-range defect formation during nonmelt laser annealing

J. A. Sharp, A. J. Smith, R. P. Webb, K. J. Kirkby, N. E. B. Cowern, D. Giubertoni, S. Gennaro, M. Bersani, M. A. Foad, P. F. Fazzini, and F. Cristiano

Appl. Phys. Lett. 92, 082109 (2008); http://dx.doi.org/10.1063/1.2885091 (3 pages) | Cited 1 time

Online Publication Date: 28 February 2008

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The effects of surface proximity and B concentration on end-of-range defect formation during nonmelt laser annealing in preamorphized silicon have been studied. These effects were analyzed by observing the activation and diffusion of an ultrashallow B implant, using Hall effect and secondary ion mass spectrometry measurements. By adjusting the preamorphizing implant and laser annealing conditions, B deactivation and diffusion were minimized, resulting in a sheet resistance of ∼ 600 Ω/sq with a 16 nm junction depth. This is attributed to a combination of enhanced dissolution of end-of-range defects and preferential formation of B-interstitial clusters due to the surface proximity and high B concentration, respectively.
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61.72.jj Interstitials
61.72.Cc Kinetics of defect formation and annealing
72.20.My Galvanomagnetic and other magnetotransport effects
66.30.Lw Diffusion of other defects
72.80.Cw Elemental semiconductors

Capacitance transient study of the influence of iron contamination on the electrical characteristics of silicon grain boundaries

Jinggang Lu and George Rozgonyi

Appl. Phys. Lett. 92, 082110 (2008); http://dx.doi.org/10.1063/1.2887880 (3 pages) | Cited 4 times

Online Publication Date: 28 February 2008

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The influence of iron contamination on the electrical characteristics of an interfacial grain boundary created by bonding two (110)/(100) silicon wafers was examined by a capacitance transient technique. Compared with the clean sample, iron contamination increases both the density of boundary states (by at least three times) and the zero-bias barrier height (by 70 meV), while dramatically reducing by two orders of magnitude the electron/hole capture cross-section ratio. These results suggest that a larger barrier will be sustained at the iron contaminated boundary under low injection condition, thereby enabling more effective minority carrier collection and associated enhanced recombination activity.
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61.72.Mm Grain and twin boundaries
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Cw Elemental semiconductors

Mobility of thin AlAs quantum wells: Theory compared to experiment

A. Gold

Appl. Phys. Lett. 92, 082111 (2008); http://dx.doi.org/10.1063/1.2887881 (3 pages) | Cited 4 times

Online Publication Date: 28 February 2008

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For interface-roughness scattering and for zero temperatures, we compare theoretical results for the transport properties of the electron gas present in thin AlAs quantum wells with experimental results for a well of width L = 45 Å. The importance of a density dependent effective mass is discussed. For the mobility, reasonable agreement between theory and experiment is obtained by taking into account multiple scattering effects, which lead to a metal-insulator transition. We predict the single-particle relaxation time. With a density dependent effective mass, the calculated critical electron density of the metal-insulator transition is found to be in good agreement with the experimental value.
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73.63.Hs Quantum wells
72.20.Fr Low-field transport and mobility; piezoresistance
73.21.Fg Quantum wells
68.35.Ct Interface structure and roughness
71.30.+h Metal-insulator transitions and other electronic transitions

Noise measurement of a quantized charge pump

N. Maire, F. Hohls, B. Kaestner, K. Pierz, H. W. Schumacher, and R. J. Haug

Appl. Phys. Lett. 92, 082112 (2008); http://dx.doi.org/10.1063/1.2885076 (3 pages) | Cited 8 times

Online Publication Date: 29 February 2008

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We study the noise properties of a gate controlled single electron pump at a driving frequency fp = 400 MHz. We observe a significant reduction of the noise power on the current plateaus. This is a strong indication for true quantized charge pumping. We furthermore observe a small level of low frequency fluctuations which indicates a good frequency stability of the pump.
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07.50.Hp Electrical noise and shielding equipment
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)

Surface passivation oxide effects on the current gain of 4H-SiC bipolar junction transistors

H.-S. Lee, M. Domeij, C.-M. Zetterling, M. Östling, F. Allerstam, and E. Ö. Sveinbjörnsson

Appl. Phys. Lett. 92, 082113 (2008); http://dx.doi.org/10.1063/1.2888965 (3 pages) | Cited 2 times

Online Publication Date: 29 February 2008

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Effects of surface recombination on the common emitter current gain have been studied in 4H-silicon carbide (SiC) bipolar junction transistors (BJTs) with passivation formed by conventional dry oxidation and with passivation formed by dry oxidation in nitrous oxide (N2O) ambient. A gradual reduction of the current gain was found after removal of the passivation oxide followed by air exposure. Comparison of the measurement results for two different passivated BJTs indicates that the BJTs with passivation by dry oxidation in nitrous oxide (N2O) ambient show a half order of magnitude reduction of base current, resulting in a half order of magnitude increase of current gain at low currents. This improvement of current gain is attributed to reduced surface recombination caused by reduced interface trap densities at the base-emitter junction sidewall.
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85.30.Pq Bipolar transistors
81.65.Rv Passivation
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Soft-magnetic materials characterized using a superconducting solenoid as magnetic source

Giovanni Mastrogiacomo, Jörg F. Löffler, and Neil R. Dilley

Appl. Phys. Lett. 92, 082501 (2008); http://dx.doi.org/10.1063/1.2838733 (3 pages) | Cited 1 time

Online Publication Date: 25 February 2008

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Magnetization measurements of soft-magnetic materials can be affected if they are characterized using a superconducting solenoid. Recording hysteresis loops while stepping the magnetic field can cause an apparently inverted hysteresis, if due to the pinned remanent flux in the magnet the field at the sample location exceeds the sample’s coercive field. Hysteresis loops recorded while sweeping the field can also be affected by ramping rate. The sweeping-rate dependence is caused by leakage currents resulting from the persistent switch and synchronization issues regarding collection of magnetic moment and field data. The resulting errors can be estimated by measuring paramagnetic dysprosium oxide.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities

Photoemission and x-ray absorption studies of valence states in (Ni,Zn,Fe,Ti)3O4 thin films exhibiting photoinduced magnetization

M. Kobayashi, Y. Ooki, M. Takizawa, G. S. Song, A. Fujimori, Y. Takeda, K. Terai, T. Okane, S.-I. Fujimori, Y. Saitoh, H. Yamagami, M. Seki, T. Kawai, and H. Tabata

Appl. Phys. Lett. 92, 082502 (2008); http://dx.doi.org/10.1063/1.2885080 (3 pages) | Cited 1 time

Online Publication Date: 25 February 2008

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By means of photoemission and x-ray absorption spectroscopy, we have studied the electronic structure of (Ni,Zn,Fe,Ti)3O4 thin films, which exhibits a cluster glass behavior with a spin-freezing temperature Tf of ∼ 230 K and photoinduced magnetization (PIM) below Tf. The Ni and Zn ions were found to be in the divalent states. Most of the Fe and Ti ions in the thin films were trivalent (Fe3+) and tetravalent (Ti4+), respectively. While Ti doping did not affect the valence states of the Ni and Zn ions, a small amount of Fe2+ ions increased with Ti concentration, consistent with the proposed charge-transfer mechanism of PIM.
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75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Gg Ferrimagnetics
75.50.Lk Spin glasses and other random magnets
79.60.Dp Adsorbed layers and thin films
78.70.Dm X-ray absorption spectra

Origin of uniaxial magnetic anisotropy in epitaxial MnAs film on GaAs(001) substrate

Kwang-Su Ryu, JinBae Kim, YoungPak Lee, Hiro Akinaga, Takashi Manago, Ravindranath Viswan, and Sung-Chul Shin

Appl. Phys. Lett. 92, 082503 (2008); http://dx.doi.org/10.1063/1.2844856 (3 pages) | Cited 9 times

Online Publication Date: 25 February 2008

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We investigate the origin of in-plane uniaxial magnetic anisotropy of epitaxial ferromagnetic MnAs film on GaAs(001). Interestingly, as temperature increases, the in-plane uniaxial magnetic anisotropy along the MnAs[11math0] direction changes and then disappears. Direct microscopic domain observations show that the type of domain structure changes from a simple domain to a closure one with increasing temperature. From these results, the temperature-dependent change of the in-plane magnetic anisotropy is ascribed to a decrease in the shape anisotropy induced by the decrease in the width of the ferromagnetic α-stripe.
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75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
75.60.Ch Domain walls and domain structure

Minimizing the linewidth of the flux-flow oscillator

Andrey L. Pankratov

Appl. Phys. Lett. 92, 082504 (2008); http://dx.doi.org/10.1063/1.2839605 (3 pages) | Cited 5 times

Online Publication Date: 26 February 2008

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The linewidth of the flux-flow oscillator has been calculated by direct computer simulation of the sine-Gordon equation with noise. Good agreement of the numerical results with the formula derived in Phys. Rev. B 65, 054504 (2002) has been achieved. Depending on the length of the unbiased tail, the power may be maximized and the linewidth may be minimized in a broad range of bias currents. The linewidth can be decreased further by 1.5 times by proper load matching.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Gz Optical properties
74.50.+r Tunneling phenomena; Josephson effects

Control of epitaxy-induced magnetocrystalline anisotropy in a molecular beam epitaxy–grown Co/MgO/Fe/MgO(100) pseudo-spin-valve

J.-B. Laloë, A. Ionescu, T. J. Hayward, J. Llandro, J. A. C. Bland, and M. E. Vickers

Appl. Phys. Lett. 92, 082505 (2008); http://dx.doi.org/10.1063/1.2887907 (3 pages) | Cited 1 time

Online Publication Date: 27 February 2008

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We show that by obtaining a crystalline structure in a Co/MgO/Fe tunnel junction, we are able to control the magnetic anisotropies in the spin valve and therefore, induce independent switching of the two magnetic layers. In situ and ex situ structural characterization confirms that the multilayer is fully epitaxial, with smooth interfaces throughout. In confirmation of the high quality of the insulating barrier, we also present a layer-selective measurement of the magnetization of the top electrode using current-in-plane transport measurements.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.66.Fn Inorganic compounds
75.45.+j Macroscopic quantum phenomena in magnetic systems

Current-driven magnetization reversal at extremely low threshold current density in (Ga,Mn)As-based double-barrier magnetic tunnel junctions

Maya Watanabe, Jun Okabayashi, Hiroshi Toyao, Takeshi Yamaguchi, and Junji Yoshino

Appl. Phys. Lett. 92, 082506 (2008); http://dx.doi.org/10.1063/1.2841703 (3 pages) | Cited 11 times

Online Publication Date: 28 February 2008

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Current-driven magnetic orientation reversal at an extremely low threshold current density, as low as 2.0×104 A/cm2, has been achieved in (Ga,Mn)As-based double-barrier magnetic tunneling junctions (MTJs) sandwiched between top and bottom MTJs. The middle magnetic free layer thickness dependence clearly demonstrates that the low threshold current density is owing not only to the small magnetization of the magnetic free layer but also the enhancement of the spin torque caused by a spin-polarized current through the top and bottom MTJs.
Show PACS
75.60.Jk Magnetization reversal mechanisms
75.50.Pp Magnetic semiconductors
72.25.Dc Spin polarized transport in semiconductors
75.47.Pq Other materials
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