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28 Nov 2011

Volume 99, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 221902 (2011); http://dx.doi.org/10.1063/1.3663578 (3 pages)

Aparna Deshpande, Kai Felix Braun, and Saw-Wai Hla
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Quantum Hall-like effect in gated four-terminal graphene devices without magnetic field

Mou Yang, Xian-Jin Ran, Yan Cui, and Rui-Qiang Wang

Appl. Phys. Lett. 99, 222101 (2011); http://dx.doi.org/10.1063/1.3663625 (3 pages) | Cited 2 times

Online Publication Date: 28 November 2011

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We investigate the transport properties of a four-terminal graphene device of which two terminals are beneath a pair of reversal top gate voltages. We find there exists quantum Hall-like effect without magnetic field applied. The curve of Hall conductance versus the Fermi energy shows steps, and the disorder can make the steps clearer. The average length of Hall conductance plateaus is of the order meV for the devices with the terminal widths of the order μm, which is within the scope of the experimental observation. The influences of gate voltage, device dimensions, and dispersion gap are also discussed.
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73.43.-f Quantum Hall effects
72.80.Vp Electronic transport in graphene
73.20.At Surface states, band structure, electron density of states

Localized charge trapping and lateral charge diffusion in metal nanocrystal-embedded High-κ/SiO2 gate stack

Z. Z. Lwin, K. L. Pey, C. Liu, Q. Liu, Q. Zhang, Y. N. Chen, P. K. Singh, and S. Mahapatra

Appl. Phys. Lett. 99, 222102 (2011); http://dx.doi.org/10.1063/1.3664220 (3 pages) | Cited 1 time

Online Publication Date: 28 November 2011

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In this work, we demonstrate a two-step analysis procedure that enables an in-depth understanding of the localized charge trapping and charge decay mechanisms in metal nanocrystal (MNC)-embedded high-κ/SiO2 gate stacks. The results clearly reveal that vertical charge loss and lateral charge diffusion are two competing mechanisms, and they can be identified by discharging current measurements at elevated temperatures and the Kelvin force microscopy characterization. It is found that the MNC with higher work function has a lower inter-dot charge tunneling probability, which is favorable for improved retention in memory applications. However, the vertical charge loss during the initial decay period is a trade-off and it could be minimized by using a dual-layer MNC structure.
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84.30.Sk Pulse and digital circuits
73.63.Bd Nanocrystalline materials

Intrinsic defects and electronic conductivity of TaON: First-principles insights

Shiyou Chen and Lin-Wang Wang

Appl. Phys. Lett. 99, 222103 (2011); http://dx.doi.org/10.1063/1.3664346 (3 pages) | Cited 4 times

Online Publication Date: 28 November 2011

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Using hybrid functional calculations we show that TaON has different defect properties from the binary tantalum oxide and nitride: (i) instead of O or N vacancies or Ta interstitials, the ON antisite is the dominant defect, which determines its intrinsic n-type conductivity and the p-type doping difficulty; (ii) the ON antisite has a shallower donor level than O or N vacancies, with a delocalized distribution composed mainly of the Ta 5d orbitals, which gives rise to better electronic conductivity in the oxynitride than in the oxide and nitride. The phase stability analysis reveals that further oxidation of TaON is possible when the oxygen chemical potential is high (O rich); thus, a low oxygen partial pressure is required to synthesize stoichiometric TaON samples.
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71.55.Ht Other nonmetals
72.80.Sk Insulators
61.72.up Other materials
61.72.jd Vacancies
61.72.jj Interstitials

Effect of H on interface properties of Al2O3/In0.53Ga0.47As

Zuoguang Liu, Sharon Cui, Pini Shekhter, Xiao Sun, Lior Kornblum, Jie Yang, Moshe Eizenberg, K. S. Chang-Liao, and T. P. Ma

Appl. Phys. Lett. 99, 222104 (2011); http://dx.doi.org/10.1063/1.3665395 (3 pages) | Cited 3 times

Online Publication Date: 29 November 2011

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We report that depositing Al2O3 on InGaAs in an H-containing ambient (e.g., in forming gas) results in significant reduction of interface-trap density and significantly suppressed frequency dispersion of accumulation capacitance. The results of the inelastic electron tunneling spectroscopy study reveal that strong trap features at the Al2O3/InGaAs interface in the InGaAs band gap are largely removed by depositing Al2O3 in an H-containing ambient. Transmission electron microscopy images and x-ray photoelectron spectroscopy data shed some light on the role of hydrogen in improving interface properties of the Al2O3/In0.53Ga0.47As gate stack.
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73.20.At Surface states, band structure, electron density of states
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Cliff-like conduction band offset and KCN-induced recombination barrier enhancement at the CdS/Cu2ZnSnS4 thin-film solar cell heterojunction

M. Bär, B.-A. Schubert, B. Marsen, R. G. Wilks, S. Pookpanratana, M. Blum, S. Krause, T. Unold, W. Yang, L. Weinhardt, C. Heske, and H.-W. Schock

Appl. Phys. Lett. 99, 222105 (2011); http://dx.doi.org/10.1063/1.3663327 (3 pages) | Cited 7 times

Online Publication Date: 29 November 2011

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The electronic structure of the CdS/Cu2ZnSnS4 (CZTS) heterojunction was investigated by direct and inverse photoemission. The effects of a KCN etch of the CZTS absorber prior to CdS deposition on the band alignment at the respective interface were studied. We find a “cliff”-like conduction band offset at the CdS/CZTS interface independent of absorber pretreatment and a significant etch-induced enhancement of the energetic barrier for charge carrier recombination across the CdS/CZTS interface.
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88.40.H- Solar cells (photovoltaics)
72.20.Fr Low-field transport and mobility; piezoresistance
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
79.60.-i Photoemission and photoelectron spectra
68.55.ag Semiconductors
88.40.J- Types of solar cells

Anisotropic effect of piezoelectric polarization on Schottky barrier height in elastically deformed bulk GaN crystal

Masaki Fujikane (藤金 正樹), Toshiya Yokogawa (横川 俊哉), Shijo Nagao (長尾 至成), and Roman Nowak

Appl. Phys. Lett. 99, 222106 (2011); http://dx.doi.org/10.1063/1.3665250 (3 pages) | Cited 1 time

Online Publication Date: 30 November 2011

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We studied electrical characteristics in c-pane (0001) and m-plane (10−10) GaN by nanoindentation examination with a conductive diamond indenter. At constant voltage during partial indentation, the current density increased stepwise as the loading–unloading cycle went by in c-plane GaN and was constant in m-plane GaN. During several constant-indentation loads, the turn-on voltage decreased with increasing indentation load in c-plane GaN and was constant in m-plane GaN. We investigated the piezoelectric polarization anisotropy by in situ electric measurement while controlling strain in GaN crystals.
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73.30.+y Surface double layers, Schottky barriers, and work functions
77.22.Ej Polarization and depolarization
77.65.-j Piezoelectricity and electromechanical effects
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness

Transport properties in single-crystalline rutile TiO2 nanorods

R. S. Chen, C. A. Chen, W. C. Wang, H. Y. Tsai, and Y. S. Huang

Appl. Phys. Lett. 99, 222107 (2011); http://dx.doi.org/10.1063/1.3665635 (3 pages) | Cited 4 times

Online Publication Date: 30 November 2011

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Electronic transport properties of the single-crystalline titanium dioxide (TiO2) nanorods (NRs) with single rutile phase have been investigated. The conductivity values for the individual TiO2 NRs grown by metal-organic chemical vapor deposition are in the range of 1−10 Ω−1 cm−1. The temperature-dependent measurement shows the presence of two shallow donor levels/bands with activation energies at 8 and 28 meV, respectively. On the photoconductivity (PC), the TiO2 NRs exhibit the much higher normalized PC gain and sensitive excitation-power dependence than the polycrystalline nanotubes. The results demonstrate the superior photoconduction efficiency and distinct mechanism in the monocrystalline one-dimensional TiO2 nanostructures in comparison to the polycrystalline or nanoporous counterparts.
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72.40.+w Photoconduction and photovoltaic effects
73.63.Fg Nanotubes
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.16.-c Methods of micro- and nanofabrication and processing
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)
71.55.Ht Other nonmetals

Ab-initio simulations of deformation potentials and electron mobility in chemically modified graphene and two-dimensional hexagonal boron-nitride

Samantha Bruzzone and Gianluca Fiori

Appl. Phys. Lett. 99, 222108 (2011); http://dx.doi.org/10.1063/1.3665183 (3 pages) | Cited 6 times

Online Publication Date: 1 December 2011

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We present an ab-initio study of electron mobility and electron-phonon coupling in chemically modified graphene, considering fluorinated and hydrogenated graphene at different percentage coverage. Hexagonal boron carbon nitrogen is also investigated due the increased interest shown by the research community towards this material. In particular, the deformation potentials are computed by means of density functional theory, while the carrier mobility is obtained according to the Takagi model (S. Takagi, A. Toriumi, and H. Tango, IEEE Trans. Electron Devices 41, 2363 (1994)). We will show that graphene with a reduced degree of hydrogenation can compete, in terms of mobility, with silicon technology.
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72.20.Fr Low-field transport and mobility; piezoresistance
73.61.Wp Fullerenes and related materials
63.22.Rc Phonons in graphene
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
63.20.kd Phonon-electron interactions

Electronic interaction and bipolar resistive switching in copper oxide-multilayer graphene hybrid interface: Graphene as an oxygen ion storage and blocking layer

Bharti Singh, B. R. Mehta, Govind, X. Feng, and Klaus Müllen

Appl. Phys. Lett. 99, 222109 (2011); http://dx.doi.org/10.1063/1.3663971 (3 pages) | Cited 1 time

Online Publication Date: 1 December 2011

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This study reports a bipolar resistive switching device based on copper oxide (CuO)-multilayer graphene (MLG) hybrid interface in complete contrast to the ohmic and rectifying characteristics of junctions based on individual MLG and CuO layers. The observed shift and the occurrence of additional O1s, Cu2p, and C1s core level peaks indicate electronic interaction at the hybrid interfacial layer. Large changes in the resistive switching parameters on changing the ambient conditions from air to vacuum establish the important role of MLG as oxygen ion storage and blocking layer towards the observed resistive switching effect.
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85.65.+h Molecular electronic devices
84.30.Jc Power electronics; power supply circuits
84.32.Dd Connectors, relays, and switches
85.30.Pq Bipolar transistors
85.40.Xx Hybrid microelectronics; thick films

Role of copper in time dependent dielectric breakdown of porous organo-silicate glass low-k materials

Larry Zhao, Marianna Pantouvaki, Kristof Croes, Zsolt Tőkei, Yohan Barbarin, Christopher J. Wilson, Mikhail R. Baklanov, Gerald P. Beyer, and Cor Claeys

Appl. Phys. Lett. 99, 222110 (2011); http://dx.doi.org/10.1063/1.3664405 (3 pages) | Cited 2 times

Online Publication Date: 1 December 2011

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The role of copper in time dependent dielectric breakdown (TDDB) of a porous low-k dielectric with TaN/Ta barrier was investigated on a metal-insulator-metal capacitor configuration where Cu ions can drift into the low-k film by applying a positive potential on the top while they are not permitted to enter the low-k dielectric if a negative potential is applied on the top. No difference in TDDB performance was observed between the positive and negative bias conditions, suggesting that Cu cannot penetrate TaN/Ta barrier to play a critical role in the TDDB of porous low-k material.
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81.05.Kf Glasses (including metallic glasses)
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.05.Rm Porous materials; granular materials
84.32.Tt Capacitors
77.55.Bh Low-permittivity dielectric films
77.22.Jp Dielectric breakdown and space-charge effects

Effect of transverse electric field on helical edge states in a quantum spin-Hall system

Genhua Liu, Guanghui Zhou, and Yong-Hai Chen

Appl. Phys. Lett. 99, 222111 (2011); http://dx.doi.org/10.1063/1.3664776 (3 pages) | Cited 4 times

Online Publication Date: 2 December 2011

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We study the electronic band, density distribution, and transport property for a HgTe/CdTe quantum well Hall bar with finite-width in the presence of a transverse electric field. It is found that the electric field can lead to a topological phase transition which controls edge state properties. Interestingly, the chirality of edge states can be modified under electric field, and a sufficient high field can remove the spectrum gap induced by the coupling between the edge states in a narrow Hall bar, restoring quantum spin-Hall effect. These findings may provide a fundamental understanding of topological edge states.
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81.05.Dz II-VI semiconductors
81.07.St Quantum wells
73.63.Hs Quantum wells
73.43.-f Quantum Hall effects
73.21.Fg Quantum wells
72.20.My Galvanomagnetic and other magnetotransport effects
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