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17 Jan 2011

Volume 98, Issue 3, Articles (03xxxx)

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Appl. Phys. Lett. 98, 031101 (2011); http://dx.doi.org/10.1063/1.3529469 (3 pages)

Sinan Balci, Askin Kocabas, Coskun Kocabas, and Atilla Aydinli
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Creation of charged excitons with two-color excitation method and initialization of electron spin qubit in quantum dots

Hideki Gotoh, Haruki Sanada, Hidehiko Kamada, Hiroshi Yamaguchi, and Tetsuomi Sogawa

Appl. Phys. Lett. 98, 032101 (2011); http://dx.doi.org/10.1063/1.3543841 (3 pages)

Online Publication Date: 18 January 2011

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An optical pumping method for creating charged excitons in semiconductor quantum dots is demonstrated using a two-color excitation method. This method employs two laser sources whose energies are in the resonant and barrier excitation conditions, respectively. The photoluminescence (PL) spectra of a single quantum dot clearly vary from exciton-originated PL to charged exciton-originated PL as the excitation conditions are changed. This method is applied to the initialization process of an electron spin qubit without a magnetic field, which provides a simple and effective way of implementing quantum computing with spin qubits.
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73.21.La Quantum dots
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.35.Pq Charged excitons (trions)
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
73.22.Lp Collective excitations

Correlation between structure and electrical transport in ion-irradiated graphene grown on Cu foils

Grant Buchowicz, Peter R. Stone, Jeremy T. Robinson, Cory D. Cress, Jeffrey W. Beeman, and Oscar D. Dubon

Appl. Phys. Lett. 98, 032102 (2011); http://dx.doi.org/10.1063/1.3536529 (3 pages) | Cited 2 times

Online Publication Date: 18 January 2011

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Graphene grown by chemical vapor deposition and supported on SiO2 and sapphire substrates was studied following the controlled introduction of defects induced by 35 keV carbon ion irradiation. Changes in Raman spectra for fluences ranging from 1012 to 1015 cm−2 indicate that the structure of graphene evolves from a highly ordered layer, to a patchwork of disordered domains, to an essentially amorphous film. These structural changes result in a dramatic decrease in the Hall mobility by orders of magnitude while, remarkably, the Hall concentration remains almost unchanged, suggesting that the Fermi level is pinned at a hole concentration near 1×1013 cm−2. A model for scattering by resonant scatterers is in good agreement with mobility measurements up to an ion fluence of 1×1014 cm−2.
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61.48.Gh Structure of graphene
73.22.Pr Electronic structure of graphene
78.67.Wj Optical properties of graphene
78.30.Na Fullerenes and related materials
61.80.Jh Ion radiation effects
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Anisotropic transport of two-dimensional electron gas modulated by embedded elongated GaSb/GaAs quantum dots

Guodong Li, Chao Jiang, Qinsheng Zhu, and Hiroyuki Sakaki

Appl. Phys. Lett. 98, 032103 (2011); http://dx.doi.org/10.1063/1.3541882 (3 pages) | Cited 2 times

Online Publication Date: 19 January 2011

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Geometrically anisotropic GaSb/GaAs quantum dots (QDs) that are elongated along the [110] direction are embedded in the vicinity of a modulation-doped AlGaAs/GaAs heterointerface. At 4.2 K, the electron mobilities μ∥ and μ⊥, which are parallel and perpendicular to the QD elongation axis, respectively, are systematically investigated as a function of the electron concentration NS by both experimental measurements and theoretical simulations. In the experiments, the mobility ratio μ∥/μ⊥ increased with increasing NS. The mobility anisotropy, attributed to the anisotropic scattering potential of the elongated GaSb QDs, is calculated under the theoretical model of a rectangular scattering potential of GaSb QDs.
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73.21.La Quantum dots
73.63.Kv Quantum dots
72.20.Fr Low-field transport and mobility; piezoresistance
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Bandstructure line-up of epitaxial Fe/MgO/Ge heterostructures: A combined x-ray photoelectron spectroscopy and transport study

M. Cantoni, D. Petti, C. Rinaldi, and R. Bertacco

Appl. Phys. Lett. 98, 032104 (2011); http://dx.doi.org/10.1063/1.3543851 (3 pages) | Cited 3 times

Online Publication Date: 19 January 2011

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The bandstructure line-up of Fe/MgO/Ge heterostructures with various Ge doping has been determined by x-ray photoemission spectroscopy. The MgO layer causes a sizable depinning of the Fermi level in Ge for light n-(1015 cm−3) and moderate p-doping (1018 cm−3), but not for heavy n-doping (1020 cm−3). The Fermi level instead stays essentially in the middle of the MgO gap for all the investigated doping. This picture agrees with transport measurements only for moderate n- or p-doping, while we demonstrate that for heavy n-doping the analysis of the conductance versus temperature fails in predicting the Schottky barrier height.
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73.20.At Surface states, band structure, electron density of states
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.30.+y Surface double layers, Schottky barriers, and work functions
61.72.U- Doping and impurity implantation
79.60.Jv Interfaces; heterostructures; nanostructures

Nonvolatile resistive switching in Pr0.7Ca0.3MnO3 devices using multilayer graphene electrodes

Wootae Lee, Gunho Jo, Sangchul Lee, Jubong Park, Minseok Jo, Joonmyoung Lee, Seungjae Jung, Seonghyun Kim, Jungho Shin, Sangsu Park, Takhee Lee, and Hyunsang Hwang

Appl. Phys. Lett. 98, 032105 (2011); http://dx.doi.org/10.1063/1.3544051 (3 pages) | Cited 1 time

Online Publication Date: 20 January 2011

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We report resistive switching in Pr0.7Ca0.3MnO3 (PCMO) devices using multilayer graphene (MLG) for nonvolatile memory applications. When MLG was used as a conducting electrode, PCMO device exhibited resistive switching with an on/off ratio of over two orders of magnitude and stable retention characteristics for over 104 s at 85 °C. Raman spectroscopy in both resistance states revealed increases in D and D′ peaks associated with defects and large shift in G peak position for high-resistance state. This was attributed to formation and dissolution of oxygenated graphene at the MLG/PCMO interface, resulting in resistive switching.
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84.30.Sk Pulse and digital circuits

Spin current generation by adiabatic pumping in monolayer graphene

Qingtian Zhang, K. S. Chan, and Zijing Lin

Appl. Phys. Lett. 98, 032106 (2011); http://dx.doi.org/10.1063/1.3544581 (3 pages) | Cited 6 times

Online Publication Date: 20 January 2011

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We propose a method of generating spin currents in monolayer graphene through adiabatic quantum pumping by two oscillating potentials. Spin splitting is induced in the graphene layer by ferromagnetic proximity. The pumped charge and spin currents are sensitive functions of the Fermi energy, which can thus be used to control the degree of polarization. The predicted pumped currents are measurable using the current technology. The proposed method is useful in the development of graphene spintronics.
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73.61.Wp Fullerenes and related materials
72.25.-b Spin polarized transport
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
73.22.Pr Electronic structure of graphene

Direct observation of the 1/E dependence of time dependent dielectric breakdown in the presence of copper

Larry Zhao, Zsolt Tőkei, Kristof Croes, Christopher J. Wilson, Mikhail Baklanov, Gerald P. Beyer, and Cor Claeys

Appl. Phys. Lett. 98, 032107 (2011); http://dx.doi.org/10.1063/1.3543850 (3 pages) | Cited 2 times

Online Publication Date: 20 January 2011

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Time dependent dielectric breakdown (TDDB) lifetime model study has been performed on a metal-insulator-semiconductor capacitor structure with copper directly deposited on silicon dioxide without a barrier material. The structure generates a low electric field acceleration of time-to-failure, which makes it possible to measure TDDB over a wide range of electric fields from 3.5 to 10 MV/cm and experimentally validate TDDB lifetime model without any assumption and data extrapolation. The experimental results are in good agreement with the so called 1/E model and do not support the E, √E, or power-law model.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
77.22.Jp Dielectric breakdown and space-charge effects
84.32.Tt Capacitors

Inelastic electron tunneling study of crystallization effects and defect energies in hafnium oxide gate dielectrics

Eun Ji Kim, Michael Shandalov, Krishna C. Saraswat, and Paul C. McIntyre

Appl. Phys. Lett. 98, 032108 (2011); http://dx.doi.org/10.1063/1.3527977 (3 pages) | Cited 1 time

Online Publication Date: 20 January 2011

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Changes in phonon spectra and point defect populations that accompany crystallization of HfO2 were investigated by inelastic tunneling across Al/HfO2/SiO2/Si. Spectral features from tetragonal- and monoclinic-HfO2 vibrational modes are observed in annealed films, while they are not detected in as-deposited samples, consistent with selected area electron diffraction analysis. In addition to features indexed as vibrational modes, peaks whose amplitude and energy vary with bias history were detected for p-type Si. We attribute these features to point defect-related states in the HfO2 band gap and find good agreement between their energies and those predicted theoretically for oxygen vacancy levels in HfO2.
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73.40.Gk Tunneling
77.55.D- High-permittivity gate dielectric films
81.40.Gh Other heat and thermomechanical treatments
71.55.Ht Other nonmetals
71.20.Ps Other inorganic compounds
61.72.jd Vacancies

Disorder induced Coulomb gaps in graphene constrictions with different aspect ratios

B. Terrés, J. Dauber, C. Volk, S. Trellenkamp, U. Wichmann, and C. Stampfer

Appl. Phys. Lett. 98, 032109 (2011); http://dx.doi.org/10.1063/1.3544580 (3 pages) | Cited 1 time

Online Publication Date: 21 January 2011

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We present electron transport measurements on lithographically defined and etched graphene nanoconstrictions with different aspect ratios including different lengths (l) and widths (w). A roughly length-independent disorder induced effective energy gap can be observed around the charge neutrality point. This energy gap scales inversely with the width even in regimes where the length of the constriction is smaller than its width (l<w). In very short constrictions, we observe both resonances due to localized states or charged islands and an elevated overall conductance level (0.1−1e2/h), which is strongly length-dependent in the gap region. This makes very short graphene constrictions interesting for highly transparent graphene tunneling barriers.
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73.22.Pr Electronic structure of graphene
73.40.Gk Tunneling
72.80.Vp Electronic transport in graphene

Nanowatt logic stochastic resonance in branched resonant tunneling diodes

F. Hartmann, A. Forchel, I. Neri, L. Gammaitoni, and L. Worschech

Appl. Phys. Lett. 98, 032110 (2011); http://dx.doi.org/10.1063/1.3548539 (3 pages) | Cited 2 times

Online Publication Date: 21 January 2011

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The authors have fabricated branched resonant tunneling diodes (RTDs). Using two branches as inputs, universal logic-gate operation was investigated as a function of noise added to the input signal. The difference in the output voltage, used as a measure for logic operation, shows a peak in the noise power characteristic associated with logic stochastic resonance. The split RTD allows morphing between universal logic-gates solely controlled by the noise level with power differences in the nanowatt range.
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85.75.Mm Spin polarized resonant tunnel junctions
84.30.Sk Pulse and digital circuits

Phonon-limited and effective low-field mobility in n- and p-type [100]-, [110]-, and [111]-oriented Si nanowire transistors

Mathieu Luisier

Appl. Phys. Lett. 98, 032111 (2011); http://dx.doi.org/10.1063/1.3540689 (3 pages) | Cited 10 times

Online Publication Date: 21 January 2011

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Ultrascaled n- and p-type Si nanowire field-effect transistors (NW FETs) with [100], [110], and [111] as channel orientations are simulated in the presence of electron-phonon scattering using an atomistic quantum transport solver based on the sp3d5s∗ tight-binding model for electrons and holes, a modified Keating model for phonons, and the nonequilibrium Green’s function formalism. The channel resistances of devices with different gate lengths and carrier concentrations are computed at room temperature and used to extract phonon-limited, ballistic, and effective low-field mobilities. It is found that a [110] channel represents the best choice for high n- and p-type NW FET performances.
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85.30.Tv Field effect devices
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)
81.07.Vb Quantum wires
85.75.Hh Spin polarized field effect transistors
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