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20 Apr 2009

Volume 94, Issue 16, Articles (16xxxx)

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Appl. Phys. Lett. 94, 161105 (2009); http://dx.doi.org/10.1063/1.3119666 (3 pages)

Artur R. Davoyan, Ilya V. Shadrivov, Andrey A. Sukhorukov, and Yuri S. Kivshar
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Detection of Ga suboxides and their impact on III-V passivation and Fermi-level pinning

C. L. Hinkle, M. Milojevic, B. Brennan, A. M. Sonnet, F. S. Aguirre-Tostado, G. J. Hughes, E. M. Vogel, and R. M. Wallace

Appl. Phys. Lett. 94, 162101 (2009); http://dx.doi.org/10.1063/1.3120546 (3 pages) | Cited 70 times

Online Publication Date: 20 April 2009

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The passivation of interface states remains an important problem for III-V based semiconductor devices. The role of the most stable bound native oxides GaOx (0.5 ≤ x ≤ 1.5) is of particular interest. Using monochromatic x-ray photoelectron spectroscopy in conjunction with controlled GaAs(100) and InGaAs(100) surfaces, a stable suboxide (Ga2O) bond is detected at the interface but does not appear to be detrimental to device characteristics. In contrast, the removal of the Ga 3+ oxidation state (Ga2O3) is shown to result in the reduction of frequency dispersion in capacitors and greatly improved performance in III-V based devices.
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84.32.Tt Capacitors
81.65.Rv Passivation
73.20.At Surface states, band structure, electron density of states
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Thermal activation energy for the passivation of the n-type crystalline silicon surface by hydrogenated amorphous silicon

Jonathon Mitchell, Daniel Macdonald, and Andres Cuevas

Appl. Phys. Lett. 94, 162102 (2009); http://dx.doi.org/10.1063/1.3120765 (3 pages) | Cited 7 times

Online Publication Date: 20 April 2009

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Excellent surface passivation of crystalline silicon wafers is known to occur following post-deposition thermal annealing of intrinsic a-Si:H thin-film layers deposited by plasma-enhanced chemical vapor deposition. In this work, layer thicknesses ranging from 5 to 50 nm were used to indirectly study the surface passivation mechanism by sequentially measuring the effective carrier lifetime as a function of annealing time and temperature. From this, an activation energy of 0.7±0.1 eV was calculated, suggesting that surface passivation is reaction-limited and not determined by a bulk hydrogen diffusion process. We conclude that the primary surface reaction stems from surface rearrangement of hydrogen already near the interface.
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81.65.Rv Passivation
73.61.Jc Amorphous semiconductors; glasses
73.61.Cw Elemental semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
81.40.Gh Other heat and thermomechanical treatments
66.30.Lw Diffusion of other defects

Nonthermal origin of electromigration at gold nanojunctions in the ballistic regime

A. Umeno and K. Hirakawa

Appl. Phys. Lett. 94, 162103 (2009); http://dx.doi.org/10.1063/1.3124654 (3 pages) | Cited 7 times

Online Publication Date: 21 April 2009

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We have investigated the electromigration process at gold nanojunctions as small as several tens of atoms. Junction conductance showed successive drops by one conductance quantum, corresponding to one-by-one removal of gold atoms, only when the junction voltage exceeded certain critical values. The peak position in the histogram of the observed critical voltages agreed with the activation energies for surface diffusion of gold atoms. This fact indicates that the elementary process of electromigration in such small junctions is the self-diffusion of metal atoms driven by microscopic kinetic energy transfer from a single conduction electron to a single metal atom.
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66.30.Qa Electromigration
68.35.Fx Diffusion; interface formation
66.30.Pa Diffusion in nanoscale solids
73.23.Ad Ballistic transport

Intersubband exchange interaction induced by optically excited electron spins in GaAs/AlGaAs quantum wells

K. Morita, H. Sanada, S. Matsuzaka, Y. Ohno, and H. Ohno

Appl. Phys. Lett. 94, 162104 (2009); http://dx.doi.org/10.1063/1.3118584 (3 pages) | Cited 2 times

Online Publication Date: 21 April 2009

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Spin-dependent intersubband excitonic interactions have been investigated in GaAs/AlGaAs quantum wells by two-color pump and probe spectroscopy. We generated spin-polarized electrons in the lowest subband by resonant excitation of the heavy-hole exciton (E1-HH1) and observed polarization-dependent broadening of the second-subband exciton resonance (E2-HH2 and E2-LH1). The exchange interaction between the first and the second-subband excitons is found to play a crucial role in polarization-dependent spectral modulation as well as spin-independent Coulomb screening.
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78.66.Fd III-V semiconductors
71.35.-y Excitons and related phenomena
71.70.Gm Exchange interactions

Amorphous silicon thin-film transistors with field-effect mobilities of 2 cm2/V s for electrons and 0.1 cm2/V s for holes

Lin Han, Prashant Mandlik, Kunigunde H. Cherenack, and Sigurd Wagner

Appl. Phys. Lett. 94, 162105 (2009); http://dx.doi.org/10.1063/1.3119636 (3 pages) | Cited 8 times

Online Publication Date: 21 April 2009

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A new gate dielectric material is used to fabricate hydrogenated amorphous-silicon (a-Si:H) thin-film transistors (TFTs) with high field-effect mobilities. The dielectric is a homogeneous SiO2-silicone hybrid, which is deposited by plasma-enhanced chemical vapor deposition system at nominal room temperature. This new dielectric results in a-Si:H TFTs with measured field-effect mobilities of ∼ 2 cm2/V s for electrons and ∼ 0.1 cm2/V s for holes.
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85.30.Tv Field effect devices
81.05.Cy Elemental semiconductors
81.05.Gc Amorphous semiconductors

Ultradense phosphorus in germanium delta-doped layers

G. Scappucci, G. Capellini, W. C. T. Lee, and M. Y. Simmons

Appl. Phys. Lett. 94, 162106 (2009); http://dx.doi.org/10.1063/1.3123391 (3 pages) | Cited 8 times

Online Publication Date: 21 April 2009

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Phosphorus (P) in germanium (Ge) δ-doped layers are fabricated in ultrahigh vacuum by adsorption of phosphine molecules onto an atomically flat clean Ge(001) surface followed by thermal incorporation of P into the lattice and epitaxial Ge overgrowth by molecular beam epitaxy. Structural and electrical characterizations show that P atoms are confined, with minimal diffusion, into an ultranarrow 2-nm-wide layer with an electrically active sheet carrier concentration of 4×1013 cm−2 at 4.2 K. These results open up the possibility of ultranarrow source/drain regions with unprecedented carrier densities for Ge n-channel field effect transistors.
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73.61.Cw Elemental semiconductors
68.55.ag Semiconductors
68.43.Mn Adsorption kinetics
61.72.uf Ge and Si
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
85.30.Tv Field effect devices

Effect of In–Ga intermixing on the electronic states in self-assembled InAs quantum dots probed by nanogap electrodes

K. Shibata, M. Jung, K. M. Cha, M. Sotome, and K. Hirakawa

Appl. Phys. Lett. 94, 162107 (2009); http://dx.doi.org/10.1063/1.3123816 (3 pages) | Cited 5 times

Online Publication Date: 22 April 2009

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We have investigated the effect of In–Ga intermixing on the electronic states in single self-assembled InAs quantum dots (QDs) coupled to nanogap metallic electrodes. The orbital quantization energies of the QDs and the tunnel resistances exhibited a strong dependence on growth temperature, TG, due to In–Ga intermixing during QD formation. When the intermixing was suppressed by reducing TG to 470 °C, the electron wave functions in the QDs become more extended in space and QD-electrode coupling sufficiently strong to form the Kondo singlet states at 4.3 K was realized even in a small QD of ∼ 45 nm diameter.
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73.21.La Quantum dots
82.45.Fk Electrodes
73.40.Gk Tunneling
81.07.Ta Quantum dots

Epitaxial growth and transport properties of Bi2Sr2Co2Oy thin films by metal organic deposition

Shufang Wang, Zicai Zhang, Liping He, Mingjing Chen, Wei Yu, and Guangsheng Fu

Appl. Phys. Lett. 94, 162108 (2009); http://dx.doi.org/10.1063/1.3122930 (3 pages) | Cited 4 times

Online Publication Date: 22 April 2009

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Epitaxial Bi2Sr2Co2Oy thin films have been grown on LaAlO3 (001) by metal organic deposition. Detailed x-ray diffraction texture measurements reveal the excellent c-axis and ab-plane alignments. At 300 K, the ab-plane power factor is estimated to be more than two times larger than that of the single crystals due to the very low resistivity and the reasonably large Seebeck coefficient of the films. In addition, a large ab-plane negative magnetoresistance of 38% related to the suppression of the spin scattering is also observed in the films at low temperature.
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68.55.aj Insulators
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.Ng Insulators
73.50.Lw Thermoelectric effects

Optically controlled spin polarization in a spin transistor

Hai-Feng Lü, Yong Guo, Xiao-Tao Zu, and Huai-Wu Zhang

Appl. Phys. Lett. 94, 162109 (2009); http://dx.doi.org/10.1063/1.3111442 (3 pages) | Cited 8 times

Online Publication Date: 22 April 2009

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The authors investigate the spin-polarized transport through a quantum dot irradiated by continuous circularly polarized light. For the two-terminal dot device, it is shown that sign reversal of current polarization can be modulated for a range of bias voltage. The system thus operates as a rectifier for spin-current polarization. A three-terminal device is proposed to optimize the degree of spin polarization, which can be modulated arbitrarily by polarized optical pumping in the relative large bias voltage and high temperature.
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72.25.Fe Optical creation of spin polarized carriers
68.65.Hb Quantum dots (patterned in quantum wells)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.63.Kv Quantum dots

Doping modulation in GaN imaged by cross-sectional scanning tunneling microscopy

H. Eisele, L. Ivanova, S. Borisova, M. Dähne, M. Winkelnkemper, and Ph. Ebert

Appl. Phys. Lett. 94, 162110 (2009); http://dx.doi.org/10.1063/1.3123258 (3 pages) | Cited 5 times

Online Publication Date: 22 April 2009

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We investigated the imaging mechanisms of a Si doping modulation in GaN by cross-sectional scanning tunneling microscopy (STM). The Si doping modulation gives rise to a voltage and tip dependent height modulation of at least 0.4 Å. The origin of the height modulation in constant-current STM images is traced to two mechanisms. A doping-induced modu-lation of the band edge energies yields a voltage dependent electronic contrast and an additional mechanical relaxation of the doping-induced strain at the cleavage surface is respon-sible for a voltage independent modulation of 0.35 Å.
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61.72.uj III-V and II-VI semiconductors
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations

A low-temperature method for improving the performance of sputter-deposited ZnO thin-film transistors with supercritical fluid

Min-Chen Chen, Ting-Chang Chang, Sheng-Yao Huang, Kuan-Chang Chang, Hung-Wei Li, Shih-Ching Chen, Jin Lu, and Yi Shi

Appl. Phys. Lett. 94, 162111 (2009); http://dx.doi.org/10.1063/1.3124658 (3 pages) | Cited 22 times

Online Publication Date: 23 April 2009

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A low-temperature method, supercritical CO2 (SCCO2) fluid technology, is employed to improve the device properties of ZnO TFT at 150 °C. In this work, the undoped ZnO films were deposited by sputter at room temperature and treated by SCCO2 fluid which is mixed with 5 ml pure H2O. After SCCO2 treatment, the on/off current ratios and threshold voltage of the device were improved significantly. From x-ray photoelectron spectroscopy analyses, the enhancements were attributed to the stronger Zn–O bonds, the hydrogen-related donors, and the reduction in dangling bonds at the grain boundary by OH passivation.
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85.30.Tv Field effect devices
85.40.Sz Deposition technology
81.65.Rv Passivation
81.15.Cd Deposition by sputtering
81.05.Dz II-VI semiconductors
79.60.Jv Interfaces; heterostructures; nanostructures

Electrical field induced precipitation reaction and percolation in Ag30Ge17Se53 amorphous electrolyte films

Liang Chen, Zhiguo Liu, Yidong Xia, Kuibo Yin, Ligang Gao, and Jiang Yin

Appl. Phys. Lett. 94, 162112 (2009); http://dx.doi.org/10.1063/1.3123251 (3 pages) | Cited 9 times

Online Publication Date: 23 April 2009

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The microstructural evolution and resistive switching of glassy Ag30Ge17Se53 electrolyte films clipped by Ag active electrode, at which a positive bias was applied, and Pt inert electrode, were investigated by transmission electron microscopy observations and I-V measurements as functions of the period of electrical field treatment. It is revealed that an electrical field induced precipitation reaction forming conductive particles with orthorhombic Ag2Se structure and followed growth and networking of these particles, leading to an electrical percolation, are responsible for the transition from high resistive to high conductive state of the system. The kinetics of the precipitation reaction was also analyzed.
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82.45.Gj Electrolytes
73.61.Jc Amorphous semiconductors; glasses
82.45.Fk Electrodes
68.55.ag Semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance

Observation of chiral quantum-Hall edge states in graphene

Dong-Keun Ki, Sanghyun Jo, and Hu-Jong Lee

Appl. Phys. Lett. 94, 162113 (2009); http://dx.doi.org/10.1063/1.3123265 (3 pages) | Cited 8 times

Online Publication Date: 23 April 2009

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In this study, we determined the chiral direction of the quantum-Hall (QH) edge states in graphene by adopting simple two-terminal conductance measurements while grounding different edge positions of the sample. The edge state with a smaller filling factor is found to more strongly interact with the electric contacts. This simple method can be conveniently used to investigate the chirality of the QH edge state with zero filling factor in graphene, which is important to understand the symmetry breaking sequence in high magnetic fields (≳25 T).
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73.43.-f Quantum Hall effects
73.40.Cg Contact resistance, contact potential
73.63.Rt Nanoscale contacts
61.48.-c Structure of fullerenes and related hollow and planar molecular structures

Photoinduced electron paramagnetic resonance study of electron traps in TiO2 crystals: Oxygen vacancies and Ti3+ ions

Shan Yang, L. E. Halliburton, A. Manivannan, P. H. Bunton, D. B. Baker, M. Klemm, S. Horn, and A. Fujishima

Appl. Phys. Lett. 94, 162114 (2009); http://dx.doi.org/10.1063/1.3124656 (3 pages) | Cited 22 times

Online Publication Date: 24 April 2009

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Electron paramagnetic resonance (EPR) is used to identify photoinduced titanium-associated electron traps in TiO2 crystals (rutile). Defect production occurs at low temperature with 442 nm laser light. Spectra with S = 1/2 and S = 1 are assigned to singly ionized and neutral oxygen vacancies, respectively. These oxygen vacancies have their unpaired spins localized on the two neighboring titanium ions aligned along the c axis. A Ti3+ ion next to a Si4+ ion, a Ti3+ self-trapped electron, and a self-trapped hole shared by two adjacent oxygen ions are also observed. Isolated substitutional Fe3+ and Cr3+ ions serve as hole traps.
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76.30.Mi Color centers and other defects
61.72.jd Vacancies
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Quantum confinement and coherence in a two-dimensional electron gas in a carbon-face 3C-SiC/6H-SiC polytype heterostructure

Jie Lu, M. V. S. Chandrashekhar, J. J. Parks, D. C. Ralph, and Michael G. Spencer

Appl. Phys. Lett. 94, 162115 (2009); http://dx.doi.org/10.1063/1.3126447 (3 pages) | Cited 2 times

Online Publication Date: 24 April 2009

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We report the observation of the quantum coherence in a two-dimensional electron gas (2DEG) at a C-face 3C-/6H-SiC polytype heterostructure. Electronic confinement and coherence were observed at 1.5 K and high magnetic fields, indicating the presence and confinement of a 2DEG. The measured mobility of the 2DEG is 2000 cm2/V s and the electron sheet density is 2.7×1012/cm2.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Fq High-field and nonlinear effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.Le Other inorganic semiconductors

Photoadsorption and photodesorption for GaN

M. Foussekis, A. A. Baski, and M. A. Reshchikov

Appl. Phys. Lett. 94, 162116 (2009); http://dx.doi.org/10.1063/1.3122934 (3 pages) | Cited 10 times

Online Publication Date: 24 April 2009

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The effect of an ambient environment on the surface photovoltage and photoluminescence observed for GaN is studied. In air ambient the upward band bending gradually increases under UV illumination and is explained by the photoinduced chemisorption of surface adsorbates. Specifically, the increase in negative surface charge is consistent with the transfer of electrons from surface states or bulk to oxygen species physisorbed at the GaN surface. In contrast, the upward band bending gradually decreases in vacuum under UV illumination and can be explained by the photoinduced desorption of these species. The photoadsorption and photodesorption of negatively charged species cause the surface depletion region to increase and decrease, respectively. This change in depletion region width is consistent with the observed decrease in photoluminescence intensity in air ambient and its significant increase in vacuum for a sample with low free electron concentration.
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68.43.Tj Photon stimulated desorption
79.20.La Photon- and electron-stimulated desorption
68.43.Mn Adsorption kinetics
72.40.+w Photoconduction and photovoltaic effects
73.25.+i Surface conductivity and carrier phenomena
73.20.At Surface states, band structure, electron density of states
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