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9 Jan 2012

Volume 100, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 023701 (2012); http://dx.doi.org/10.1063/1.3673335 (3 pages)

Biswarup Pathak, Henrik Löfås, Jariyanee Prasongkit, Anton Grigoriev, Rajeev Ahuja, and Ralph H. Scheicher
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(Si)5−2y(AlP)y alloys assembled on Si(100) from Al-P-Si3 building units

T. Watkins, L. Jiang, C. Xu, A. V. G. Chizmeshya, D. J. Smith, J. Menéndez, and J. Kouvetakis

Appl. Phys. Lett. 100, 022101 (2012); http://dx.doi.org/10.1063/1.3675444 (4 pages) | Cited 3 times

Online Publication Date: 9 January 2012

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An original class of IV/III-V hybrid (Si)5−2y(AlP)y/Si(100) semiconductors have been produced via tailored interactions of molecular P(SiH3)3 and atomic Al yielding tetrahedral “Al-P-Si3” building blocks. Extensive structural, optical, and vibrational characterization corroborates that these units condense to assemble single-phase, monocrystalline alloys containing 60%-90% Si (y = 0.3-1.0) as nearly defect-free layers lattice-matched to Si. Spectroscopic ellipsometry and density functional theory band structure calculations indicate mild compositional bowing of the band gaps, suggesting that the tuning needed for optoelectronic applications should be feasible.
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68.55.ag Semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.30.Hv Other nonmetallic inorganics
78.66.Li Other semiconductors
71.20.Nr Semiconductor compounds

Noncatalytic chemical vapor deposition of graphene on high-temperature substrates for transparent electrodes

Jie Sun (孙捷), Matthew T. Cole, Niclas Lindvall, Kenneth B. K. Teo (张谋瑾), and August Yurgens

Appl. Phys. Lett. 100, 022102 (2012); http://dx.doi.org/10.1063/1.3675632 (3 pages) | Cited 13 times

Online Publication Date: 9 January 2012

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A noncatalytic chemical vapor deposition mechanism is proposed, where high precursor concentration, long deposition time, high temperature, and flat substrate are needed to grow large-area nanocrystalline graphene using hydrocarbon pyrolysis. The graphene is scalable, uniform, and with controlled thickness. It can be deposited on virtually any nonmetallic substrate that withstands ∼1000 °C. For typical examples, graphene grown directly on quartz and sapphire shows transmittance and conductivity similar to exfoliated or metal-catalyzed graphene, as evidenced by transmission spectroscopy and transport measurements. Raman spectroscopy confirms the sp2-C structure. The model and results demonstrate a promising transfer-free technique for transparent electrode production.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.63.Bd Nanocrystalline materials
78.30.Na Fullerenes and related materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
78.67.Wj Optical properties of graphene

Tuning the Schottky barrier height at MgO/metal interface

T. Jaouen, G. Jézéquel, G. Delhaye, B. Lépine, P. Turban, and P. Schieffer

Appl. Phys. Lett. 100, 022103 (2012); http://dx.doi.org/10.1063/1.3675859 (3 pages) | Cited 1 time

Online Publication Date: 9 January 2012

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We present an experimental investigation of the interface electronic structure of thin MgO films epitaxially grown on Ag(001) by x-ray and ultraviolet photoemission spectroscopy as a function of the oxide growth conditions. It is shown that the Schottky barrier height at MgO/metal interface can be tuned over 0.7 eV by a modification of the oxygen partial pressure or the sample temperature. These experimental results are explained in the framework of the extended Schottky-Mott model and the MgO-induced polarization effect by Mg enrichment of the silver surface region.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts
79.60.Jv Interfaces; heterostructures; nanostructures

Hybrid density functional theory study of band gap tuning in AlN and GaN through equibiaxial strains

Yifeng Duan, Lixia Qin, Liwei Shi, Gang Tang, and Hongliang Shi

Appl. Phys. Lett. 100, 022104 (2012); http://dx.doi.org/10.1063/1.3675864 (3 pages) | Cited 3 times

Online Publication Date: 9 January 2012

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Structural transformation and the variation in the band gap of (0001) AlN and GaN films as a function of equibiaxial in-plane strain are studied using the HSE06 range-separated hybrid functional. Although AlN and GaN under strain share the same structural transition from wurtzite to a graphitelike phase, their electronic properties are significantly different. Both wurtzite and graphitelike AlN under strain can display either direct or indirect band structures, whereas the band gap of wurtzite GaN is always direct and graphitelike GaN always indirect. Furthermore, it is more difficult for AlN than GaN to obtain the graphitelike semi-metallic phase. Our results for GaN support the conclusions obtained from standard density functional theory [Dong et al., Appl. Phys. Lett. 96, 202106 (2010)]
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71.20.Nr Semiconductor compounds
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.kg Semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Spectral fluctuations of excitonic transitions of InGaAs single quantum dots

Wan Bak, Haneol Noh, Corey Stambaugh, Yasuhiko Arakawa, and Wonho Jhe

Appl. Phys. Lett. 100, 022105 (2012); http://dx.doi.org/10.1063/1.3676043 (3 pages)

Online Publication Date: 10 January 2012

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We report on our experimental study of spectral diffusion in grown InGaAs single quantum dots. Using a double-tapered tip, near-field scanning optical microscope, we obtain the spectral diffusion resulting from the quantum confined Stark effect of individual quantum dots in a randomly fluctuating electric field. These electric fields come from localized charges at defects in the vicinity of the quantum dots. In particular, we find that the similar-patterned temporal jitter, seen in the spectral diffusion, emits from a quantum dot and is dependent on the excitation density and applied bias voltage.
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78.67.Hc Quantum dots
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion
66.30.-h Diffusion in solids
68.65.Hb Quantum dots (patterned in quantum wells)
71.35.-y Excitons and related phenomena
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Controllable tunnel coupling and molecular states in a graphene double quantum dot

Lin-Jun Wang, Hai-Ou Li, Tao Tu, Gang Cao, Cheng Zhou, Xiao-Jie Hao, Zhan Su, Ming Xiao, Guang-Can Guo, Albert M. Chang, and Guo-Ping Guo

Appl. Phys. Lett. 100, 022106 (2012); http://dx.doi.org/10.1063/1.3676083 (5 pages) | Cited 2 times

Online Publication Date: 10 January 2012

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We have measured a graphene double quantum dot device with multiple electrostatic gates that are used to enhance control to investigate it. At low temperatures, the transport measurements reveal honeycomb charge stability diagrams which can be tuned from weak to strong interdot tunnel coupling regimes. We precisely extract a large interdot tunnel coupling strength for this system allowing for the observation of tunnel-coupled molecular states extending over the whole double dot. This clean, highly controllable system serves as an essential building block for quantum devices in a nuclear-spin-free world.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Clustering of N impurities in ZnO

J. Furthmüller, F. Hachenberg, A. Schleife, D. Rogers, F. Hosseini Teherani, and F. Bechstedt

Appl. Phys. Lett. 100, 022107 (2012); http://dx.doi.org/10.1063/1.3675867 (3 pages) | Cited 4 times

Online Publication Date: 10 January 2012

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Ab initio density functional theory and quasiparticle calculations for the incorporation of nitrogen atoms on oxygen sites in ZnO are presented. It is demonstrated that clustering of N atoms is energetically favored over the isolated N0 substitutional impurity. Tetrahedrons of N0 give rise to promising quasiparticle band structures with impurity states slightly above the valence band maximum (VBM), which, however, shift to higher energies with increasing negative ionization. The lowest recharging level ɛ(0/−) tends to a value 0.4 eV above the VBM, which is too deep for anything other than a weak p-doping.
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71.55.Gs II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.20.Nr Semiconductor compounds

Anisotropic electrical transport properties of poly(methyl methacrylate) infiltrated aligned carbon nanotube mats

P. Mahanandia and K. K. Nanda

Appl. Phys. Lett. 100, 022108 (2012); http://dx.doi.org/10.1063/1.3675873 (3 pages)

Online Publication Date: 10 January 2012

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We report the electrical anisotropic transport properties of poly(methyl methacrylate) infiltrated aligned carbon nanotube mats. The anisotropy in the resistivity increases with decreasing temperature and the conduction mechanism in the parallel and perpendicular direction is different. Magnetoresistance (MR) studies also suggest anisotropic behavior of the infiltrated mats. Though MR is negative, an upturn is observed when the magnetic field is increased. This is due to the interplay of electron weak localization and electron-electron interactions mechanisms. Overall, infiltrated carbon nanotube mat is a good candidate for anisotropically conductive polymer composite and a simple fabrication method has been reported.
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72.20.My Galvanomagnetic and other magnetotransport effects
72.80.Le Polymers; organic compounds (including organic semiconductors)
73.20.Fz Weak or Anderson localization
75.30.Gw Magnetic anisotropy
75.47.Pq Other materials

Effect of hafnium addition on Zn-Sn-O thin film transistors fabricated by solution process

Jun Young Choi, Sang Sig Kim, and Sang Yeol Lee

Appl. Phys. Lett. 100, 022109 (2012); http://dx.doi.org/10.1063/1.3669700 (3 pages) | Cited 4 times

Online Publication Date: 11 January 2012

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The feasibility of controlling the threshold voltage (Vth) and field effect mobility (μFE) has been studied by adjusting hafnium ratio. Hafnium zinc tin oxide (HZTO) thin films were fabricated with various hafnium ratios. Vth shifted toward positive direction, and the μFE was decreased due to the decrease of carrier concentration, because hafnium acts as carrier suppressor. The subthreshold swing exhibits good properties from 1.01 to 0.44. The decrease of carrier concentration in HZTO is closely related with the decrease of the number of oxygen by hafnium ion.
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85.30.Tv Field effect devices
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.55.ag Semiconductors

Charge separation in CdSe/CdTe hetero-nanowires measured by electrostatic force microscopy

Sebastian Schäfer, Aina Reich, Zhe Wang, Tobias Kipp, and Alf Mews

Appl. Phys. Lett. 100, 022110 (2012); http://dx.doi.org/10.1063/1.3676278 (3 pages) | Cited 2 times

Online Publication Date: 12 January 2012

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The charge state of free standing axial type-II CdSe/CdTe hetero-nanowires is monitored via electrostatic force microscopy. The CdSe and the CdTe segment which are identified by Raman spectroscopy are found to be negatively and positively charged, respectively. The charge state is monitored without and with local illumination. We found that the magnitude of opposite charging in the respective nanowire segment is increasing with illumination power, which is attributed to a charge separation of the photogenerated electron-hole pairs across the CdSe/CdTe interface.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.30.Fs III-V and II-VI semiconductors
73.21.Hb Quantum wires

Top-gate thin-film transistors based on GaN channel layer

Rongsheng Chen, Wei Zhou, and Hoi Sing Kwok

Appl. Phys. Lett. 100, 022111 (2012); http://dx.doi.org/10.1063/1.3676447 (3 pages) | Cited 1 time

Online Publication Date: 13 January 2012

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Gallium nitride (GaN) thin films were utilized as active channel layer to produce top-gate n-type thin-film transistors (TFTs). GaN thin films with wurtzite structure were deposited by reactive DC magnetron sputtering technique at room temperature using liquid gallium target. The GaN TFTs exhibit good electrical performance such as field effect mobility of 1 cm2/Vs, threshold voltage of −0.4 V, on/off current ratio of 105, and subthreshold swing of 0.8 V/decade.
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85.30.Tv Field effect devices
81.15.Cd Deposition by sputtering

Anisotropy of free-carrier absorption and diffusivity in m-plane GaN

P. Ščajev, K. Jarašiūnas, Ü. Özgür, H. Morkoç, J. Leach, and T. Paskova

Appl. Phys. Lett. 100, 022112 (2012); http://dx.doi.org/10.1063/1.3674306 (4 pages)

Online Publication Date: 13 January 2012

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Polarization-dependent free-carrier absorption (FCA) in bulk m-plane GaN at 1053 nm revealed approximately 6 times stronger hole-related absorption for E⊥c than for E||c probe polarization both at low and high carrier injection levels. In contrast, FCA at 527 nm was found isotropic at low injection levels due to electron resonant transitions between the upper and lower conduction bands, whereas the anisotropic impact of holes was present only at high injection levels by temporarily blocking electron transitions. Carrier transport was also found to be anisotropic under two-photon excitation, with a ratio of 1.17 for diffusivity perpendicular and parallel to the c-axis.
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78.30.Fs III-V and II-VI semiconductors
81.05.Ea III-V semiconductors
79.20.Ws Multiphoton absorption
66.30.-h Diffusion in solids
71.20.Nr Semiconductor compounds

Ohmic contacts to n-type germanium with low specific contact resistivity

K. Gallacher, P. Velha, D. J. Paul, I. MacLaren, M. Myronov, and D. R. Leadley

Appl. Phys. Lett. 100, 022113 (2012); http://dx.doi.org/10.1063/1.3676667 (3 pages) | Cited 5 times

Online Publication Date: 13 January 2012

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A low temperature nickel process has been developed that produces Ohmic contacts to n-type germanium with specific contact resistivities down to (2.3 ± 1.8) × 10−7 Ω-cm2 for anneal temperatures of 340 °C. The low contact resistivity is attributed to the low resistivity NiGe phase which was identified using electron diffraction in a transmission electron microscope. Electrical results indicate that the linear Ohmic behaviour of the contact is attributed to quantum mechanical tunnelling through the Schottky barrier formed between the NiGe alloy and the heavily doped n-Ge.
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73.40.Ns Metal-nonmetal contacts
61.72.Cc Kinetics of defect formation and annealing
73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Cg Contact resistance, contact potential
73.40.Gk Tunneling
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