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24 Aug 2009

Volume 95, Issue 8, Articles (08xxxx)

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Appl. Phys. Lett. 95, 082507 (2009); http://dx.doi.org/10.1063/1.3186782 (3 pages)

Sang-Koog Kim, Ki-Suk Lee, and Dong-Soo Han
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Threshold field of phase change memory materials measured using phase change bridge devices

Daniel Krebs, Simone Raoux, Charles T. Rettner, Geoffrey W. Burr, Martin Salinga, and Matthias Wuttig

Appl. Phys. Lett. 95, 082101 (2009); http://dx.doi.org/10.1063/1.3210792 (3 pages) | Cited 26 times

Online Publication Date: 24 August 2009

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The threshold switching effect of phase change memory devices is typically parameterized by the threshold voltage at which this breakdown occurs. Using phase change memory bridge devices of variable length, we prove unambiguously that the important parameter for threshold switching is a critical electrical field and not a threshold voltage. By switching phase change bridge devices from the amorphous-as-deposited state, we obtain threshold fields for Ge15Sb85, Ag- and In-doped Sb2Te, Ge2Sb2Te5, and 4 nm thick Sb devices of 8.1, 19, 56, and 94 V/μm, respectively.
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81.90.+c Other topics in materials science (restricted to new topics in section 81)
42.70.-a Optical materials

Softening of the tunneling gap in modulation-doped GaAs/AlGaAs asymmetric coupled double quantum wells in magnetic fields

Y. H. Shin, Y. H. Park, C. H. Perry, J. A. Simmons, T. Takamasu, and Yongmin Kim

Appl. Phys. Lett. 95, 082102 (2009); http://dx.doi.org/10.1063/1.3213352 (3 pages)

Online Publication Date: 24 August 2009

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Magnetophotoluminescence emissions were measured from modulation doped GaAs/AlGaAs asymmetric double quantum wells, wherein a thin barrier (25 Å) was sandwiched between a single quantum well (SQW) and a single heterojuction (SHJ). In the SQW, Landau level mixing is observed at the quantum Hall states. At ν<2, the lowest Landau level transition undergoes an exciton transition. For the SHJ region, the free carrier transitions become excitonic at the crossing point of the GaAs free exciton and the tunneling band gap shows a marked softening. An exciton-exciton interaction is shown to be responsible for the behavior of the subband energy levels in magnetic fields.
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81.05.Ea III-V semiconductors
78.55.Cr III-V semiconductors
81.07.St Quantum wells
78.67.De Quantum wells
78.20.Ls Magneto-optical effects
71.35.-y Excitons and related phenomena
73.21.Fg Quantum wells
73.43.Jn Tunneling
71.70.Di Landau levels
73.40.Gk Tunneling

Influence of the interface on the electronic channel switching of a Fe–Ag thin film on a Si substrate

J. Alonso, M. L. Fdez-Gubieda, G. Sarmiento, J. M. Barandiarán, A. Svalov, I. Orue, J. Chaboy, L. Fernández Barquín, C. Meneghini, T. Neisius, and N. Kawamura

Appl. Phys. Lett. 95, 082103 (2009); http://dx.doi.org/10.1063/1.3205124 (3 pages) | Cited 1 time

Online Publication Date: 25 August 2009

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FexAg100−x granular thin films, being 20<x<70, were prepared by pulsed laser deposition. The thermal evolution of the electric resistance shows a dramatic drop in the range of 200<T<300 K, completely reversible with temperature and associated to a current switching between the granular thin film and its Si substrate. High resolution transmission electron microscopy measurements have revealed an amorphous interface between the thin film and the substrate, and x-ray absorption spectroscopy studies have demonstrated an electronic localization associated to the Fe atoms in this interface, which is intrinsically responsible for the current switching.
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73.40.Ns Metal-nonmetal contacts
73.61.At Metal and metallic alloys
68.35.Ct Interface structure and roughness
78.70.Dm X-ray absorption spectra
68.47.Fg Semiconductor surfaces

Conductance through a single impurity in the metallic zigzag carbon nanotube

Po-Yao Chang and Hsiu-Hau Lin

Appl. Phys. Lett. 95, 082104 (2009); http://dx.doi.org/10.1063/1.3213546 (3 pages) | Cited 1 time

Online Publication Date: 25 August 2009

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We investigate the conductance through a single impurity in the metallic zigzag carbon nanotube and find that it sensitively depends on the impurity strength and the bias voltage. The interplay between the current-carrying scattering states and the evanescent modes lead to rich phenomena including resonant backward scattering, perfect tunneling, and charge accumulations. In addition to the Friedel sum rule, we also find an exact relation between the conductance and the scattering phase. Finally, relevance of our findings to the realistic transport in carbon nanotubes is discussed.
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73.63.Fg Nanotubes
73.40.Gk Tunneling
61.72.S- Impurities in crystals

Ultralow noise field-effect transistor from multilayer graphene

Atindra Nath Pal and Arindam Ghosh

Appl. Phys. Lett. 95, 082105 (2009); http://dx.doi.org/10.1063/1.3206658 (3 pages) | Cited 15 times

Online Publication Date: 25 August 2009

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We present low-frequency electrical resistance fluctuations, or noise, in graphene-based field-effect devices with varying number of layers. In single-layer devices, the noise magnitude decreases with increasing carrier density, which behaved oppositely in the devices with two or larger number of layers accompanied by a suppression in noise magnitude by more than two orders in the latter case. This behavior can be explained from the influence of external electric field on graphene band structure, and provides a simple transport-based route to isolate single-layer graphene devices from those with multiple layers.
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85.30.Tv Field effect devices
73.61.Wp Fullerenes and related materials

Self-cleaning and surface recovery with arsine pretreatment in ex situ atomic-layer-deposition of Al2O3 on GaAs

Cheng-Wei Cheng, John Hennessy, Dimitri Antoniadis, and Eugene A. Fitzgerald

Appl. Phys. Lett. 95, 082106 (2009); http://dx.doi.org/10.1063/1.3213545 (3 pages) | Cited 13 times

Online Publication Date: 26 August 2009

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Annealing native oxide covered GaAs samples in Arsine(AsH3) prior to atomic-layer-deposition of Al2O3 with trimethyaluminum (TMA) and isopropanol (IPA) results in capacitance-voltage (C-V) characteristics of the treated samples that resemble the superior C-V characteristics of p-type GaAs grown by an in situ metal-organic chemical vapor deposition process. Both TMA and IPA show self-cleaning effect on removing the native oxide in ex situ process, little evidence of a native oxide was observed with high resolution transmission electron microscopy at the Al2O3/GaAs interface. The discrepancy in the C-V characteristics was observed in in situ p- and n-type GaAs samples.
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81.65.Cf Surface cleaning, etching, patterning
61.72.Cc Kinetics of defect formation and annealing
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Multiple conducting carriers generated in LaAlO3/SrTiO3 heterostructures

S. S. A. Seo, Z. Marton, W. S. Choi, G. W. J. Hassink, D. H. A. Blank, H. Y. Hwang, T. W. Noh, T. Egami, and H. N. Lee

Appl. Phys. Lett. 95, 082107 (2009); http://dx.doi.org/10.1063/1.3213390 (3 pages) | Cited 31 times

Online Publication Date: 27 August 2009

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We have found that there is more than one type of conducting carriers generated in LaAlO3/SrTiO3 heterostructures by comparing the sheet carrier density and mobility from optical transmission spectroscopy with those from dc-transport measurements. When multiple types of carriers exist, optical characterization dominantly reflects the contribution from the high-density carriers whereas dc-transport measurements may exaggerate the contribution of the high-mobility carriers even though they are present at low density. Since the low-temperature mobility determined by dc-transport in the LaAlO3/SrTiO3 heterostructures is much higher than that extracted by optical method, we attribute the origin of high-mobility transport to the low-density conducting carriers.
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72.20.Ee Mobility edges; hopping transport
72.20.My Galvanomagnetic and other magnetotransport effects
72.80.Sk Insulators

Spin-orbit engineering of semiconductor heterostructures: A spin-sensitive quantum-phase shifter

T. L. Hoai Nguyen, Henri-Jean Drouhin, Jean-Eric Wegrowe, and Guy Fishman

Appl. Phys. Lett. 95, 082108 (2009); http://dx.doi.org/10.1063/1.3211118 (3 pages)

Online Publication Date: 27 August 2009

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In noncentrosymmetric semiconductors with zinc-blende structure grown along the [110] crystallographic direction, electrons with up- and down-spins undergo different quantum-phase shifts upon tunneling, which can be viewed as resulting from spin precession around a complex magnetic field. There is no spin filtering but a pure spin dephasing. The phase shift of the transmitted wave is proportional to the overall barrier-material thickness. We show that a device incorporating a number of resonant tunnel barriers constitutes an efficient quantum-phase shifter.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors
73.40.Gk Tunneling
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Control of electric current by graphene edge structure engineering

Masayuki Yamamoto and Katsunori Wakabayashi

Appl. Phys. Lett. 95, 082109 (2009); http://dx.doi.org/10.1063/1.3206915 (3 pages) | Cited 8 times

Online Publication Date: 27 August 2009

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In graphene nanoribbon junctions, the nearly perfect transmission occurs in some junctions while the zero conductance dips due to antiresonance appear in others. We have classified the appearance of zero conductance dips for all combinations of ribbon and junction edge structures. These transport properties do not attribute to the whole junction structure but the partial corner edge structure, which indicates that one can control the electric current simply by cutting a part of nanoribbon edge. The ribbon width is expected to be narrower than 10 nm in order to observe the zero conductance dips at room temperature.
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73.63.-b Electronic transport in nanoscale materials and structures
72.20.Fr Low-field transport and mobility; piezoresistance
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems

Effect of gate orientation on dc characteristics of Si-doped, nonpolar AlGaN/GaN metal-oxide semiconductor high electron mobility transistors

C. Y. Chang, Yu-Lin Wang, B. P. Gila, A. P. Gerger, S. J. Pearton, C. F. Lo, F. Ren, Q. Sun, Yu. Zhang, and J. Han

Appl. Phys. Lett. 95, 082110 (2009); http://dx.doi.org/10.1063/1.3216576 (3 pages) | Cited 5 times

Online Publication Date: 27 August 2009

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Sc2O3/AlGaN/GaN metal-oxide-semiconductor (MOS) high electron mobility transistors were fabricated on (11math0) a-plane, Si-doped epitaxial layers grown by metal organic chemical vapor deposition on (1 math20) r-plane sapphire substrates. The gate finger direction was varied from parallel to the in-plane c-axis [0001] to the m-axis [1 0math0] direction perpendicular to the observed striations in surface morphology. The [0001] gate devices show lower drain-source current, mobility, and transconductance than their [1 0math0] counterparts, with a systematic dependence on gate finger direction. The symmetrical gate current-voltage characteristics and low gate current ( ∼ 3×10−9 A at ±5 V) confirm the effectiveness of the MOS gate, which is an attractive approach for these structures containing heavily Si-doped AlGaN.
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85.30.Tv Field effect devices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
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