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3 Oct 2011

Volume 99, Issue 14, Articles (14xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 141901 (2011); http://dx.doi.org/10.1063/1.3644948 (3 pages)

G. Kozlowski, P. Zaumseil, M. A. Schubert, Y. Yamamoto, J. Bauer, J. Matejova, T. Schulli, B. Tillack, and T. Schroeder
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High temperature step-flow growth of gallium phosphide by molecular beam epitaxy and metalorganic chemical vapor deposition

C. Ratcliff, T. J. Grassman, J. A. Carlin, and S. A. Ringel

Appl. Phys. Lett. 99, 141905 (2011); http://dx.doi.org/10.1063/1.3644956 (3 pages) | Cited 3 times

Online Publication Date: 4 October 2011

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Post-growth surface morphologies of high-temperature homoepitaxial GaP films grown by molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD) have been studied. Smooth, stepped surface morphologies of MBE-grown layers, measured by atomic force microscopy, were found for a wide range of substrate temperatures and P2:Ga flux ratios. A MOCVD-based growth study performed under similar conditions to MBE-grown samples shows a nearly identical smooth, step-flow surface morphology, presenting a convergence of growth conditions for the two different methods. The additional understanding of GaP epitaxy gained from this study will impact its use in applications that include GaP-based device technologies, III-V metamorphic buffers, and III-V materials integration with silicon.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Tuning the inter-shell splitting in self-assembled CdTe quantum dots

K. Kukliński, Ł. Kłopotowski, K. Fronc, M. Wiater, P. Wojnar, P. Rutkowski, V. Voliotis, R. Grousson, G. Karczewski, J. Kossut, and T. Wojtowicz

Appl. Phys. Lett. 99, 141906 (2011); http://dx.doi.org/10.1063/1.3643476 (3 pages)

Online Publication Date: 4 October 2011

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We present photoluminescence studies of highly excited single self-assembled CdTe quantum dots under continuous-wave and pulsed excitations. We observe appearance of emission bands related to sequential filling of s-, p- and d-shells. We analyze the inter-shell splitting for five samples, in which the dots were formed from a strained CdTe layer of different width. We find that by increasing the CdTe layer width, the inter-shell splitting increases. In a time resolved measurement, we observe a radiative cascade between transitions involving one, two, and more than two excitons.
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78.67.Hc Quantum dots
71.35.-y Excitons and related phenomena
78.55.Et II-VI semiconductors
81.05.Dz II-VI semiconductors
81.07.Ta Quantum dots

Large internal stress-assisted twin-boundary motion in Ni2MnGa ferromagnetic shape memory alloy

Z. H. Nie, D. Y. Cong, D. M. Liu, Y. Ren, M. Pötschke, S. Roth, and Y. D. Wang

Appl. Phys. Lett. 99, 141907 (2011); http://dx.doi.org/10.1063/1.3645626 (3 pages)

Online Publication Date: 4 October 2011

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The twin boundary motion driven by thermo-magnetic coupling was in-situ studied in a NiMnGa single crystal using high-energy x-ray diffraction technique. An unstable martensite with an internal stress of ∼8 MPa was obtained through a thermo-magnetic training. The triple martensite variants assisted by internal stress are distinct from the self-accommodated martensite twin variants with a stress-free state, and a single martensite-variant can be actuated only by a magnetic field of ∼0.34 T, equivalent to an actuator stress of about 1.3 MPa. The generation of so large internal stress among variants is attributed to the altered martensite nucleation sites triggered by external fields during thermo-magnetic training.
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61.72.Mm Grain and twin boundaries
75.50.Cc Other ferromagnetic metals and alloys
81.30.Kf Martensitic transformations
64.70.kd Metals and alloys
72.15.Jf Thermoelectric and thermomagnetic effects
64.60.Q- Nucleation

Electronic structure and polaronic excitation in FeVO4

A. Dixit, P. Chen, G. Lawes, and J. L. Musfeldt

Appl. Phys. Lett. 99, 141908 (2011); http://dx.doi.org/10.1063/1.3646402 (3 pages) | Cited 1 time

Online Publication Date: 4 October 2011

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We investigated the electronic properties of FeVO4 films using optical, valence band x-ray photoelectron, and infrared spectroscopies. These studies show that FeVO4 is a direct bandgap system with a 2.7 eV gap with the Fermi level in the middle of the valence band maximum and conduction band minimum. A polaronic excitation is also observed in the middle infrared, indicating the importance of charge-lattice coupling in this multiferroic material. Fits to a model for the optical response of large polarons yield a binding energy of approximately 130 meV.
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71.20.Ps Other inorganic compounds
78.66.Nk Insulators
71.15.Nc Total energy and cohesive energy calculations
78.30.Hv Other nonmetallic inorganics
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Ab initio calculations on Li-ion migration in Li2FeSiO4 cathode material with a P21 symmetry structure

Dawei Su, Hyojun Ahn, and Guoxiu Wang

Appl. Phys. Lett. 99, 141909 (2011); http://dx.doi.org/10.1063/1.3645617 (3 pages) | Cited 2 times

Online Publication Date: 5 October 2011

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We have systematically investigated the diffusion mechanism of Li ions in Li2FeSiO4 and its delithiated product LiFeSiO4 based on the P21 symmetry using the first principle method. Calculations on the energy barriers for possible spatial hopping pathways predicted that the activation barriers along the [101] direction and Li ion layer in the ac plane are relatively low, which can ensure the facile lithium diffusion along those directions. The results indicate that Li2FeSiO4 with the P21 symmetry is an ionic conductor for Li ions with two-dimensional diffusion.
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66.30.J- Diffusion of impurities
82.45.Fk Electrodes

Improved interfacial local structural ordering of epitaxial Fe3Si(001) thin films on GaAs(001) by a MgO(001) tunneling barrier

S. I. Makarov, B. Krumme, F. Stromberg, C. Weis, W. Keune, and H. Wende

Appl. Phys. Lett. 99, 141910 (2011); http://dx.doi.org/10.1063/1.3646390 (3 pages) | Cited 2 times

Online Publication Date: 5 October 2011

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Although the quasi-Heusler compound Fe3Si is a promising candidate for spintronics applications, its combination with the reactive GaAs surface is problematic, since it deteriorates its beneficial attributes due to a large amount of interdiffusion at the Fe3Si/GaAs interface. Here, we show the epitaxial growth of Fe3Si with low evaporation rates on GaAs(001) and report on improved local structural D03 ordering in epitaxial Fe3Si(001) films grown on GaAs(001) by inserting a MgO buffer layer. Conversion-electron Mössbauer spectroscopy with 57Fe3Si tracer layers reveals that the effect of thermally induced interdiffusion at the Fe3Si/GaAs(001) interface is dramatically reduced by inserting a 30 Å MgO tunneling barrier between the film and the substrate. The chemical order of Fe3Si is comparable to that of Fe3Si films which are grown directly on MgO(001) single crystals. It is proposed that this preparation method can be useful to achieve high-efficiency spin-polarized electron currents from ferromagnetic Fe3Si into semiconducting GaAs(001).
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68.35.Ct Interface structure and roughness
72.25.-b Spin polarized transport
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.A- Nucleation and growth
66.30.Ny Chemical interdiffusion; diffusion barriers
75.70.Ak Magnetic properties of monolayers and thin films

Optical investigation of reduced graphene oxide by spectroscopic ellipsometry and the band-gap tuning

Y. Shen, P. Zhou, Q. Q. Sun, L. Wan, J. Li, L. Y. Chen, D. W. Zhang, and X. B. Wang

Appl. Phys. Lett. 99, 141911 (2011); http://dx.doi.org/10.1063/1.3646908 (3 pages) | Cited 5 times

Online Publication Date: 5 October 2011

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Spectroscopic ellipsometry was used to characterize the optical response of few layer reduced graphene oxide and graphene oxide in visible range. Lorentz oscillator model is added to analyze the ellipsometric parameters. The experiment shows the optical response of few layer reduced graphene oxide and monolayer exfoliated graphene in visible range is quite similar with slight difference due to the structure defects. The Lorentz oscillator model gives experimental support to investigate the band-gap tuning through the reduction process in details.
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78.67.Wj Optical properties of graphene
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Na Fullerenes and related materials
78.40.Ri Fullerenes and related materials

How much room for BiGa heteroantisites in GaAs1−xBix?

G. Ciatto, P. Alippi, A. Amore Bonapasta, and T. Tiedje

Appl. Phys. Lett. 99, 141912 (2011); http://dx.doi.org/10.1063/1.3647635 (3 pages) | Cited 7 times

Online Publication Date: 6 October 2011

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We addressed the issue of bismuth heteroantisite defects (BiGa) in GaAs1−xBix/GaAs epilayers by coupling x-ray absorption spectroscopy at the bismuth edge with density functional theory calculations of the defect structure. Calculations predict a large relaxation of the Bi-As interatomic distances when Bi atoms substitute Ga, however we found no experimental evidence of it. Quantitative analysis of the x-ray absorption spectra allows us to establish a maximum concentration limit for BiGa, which corresponds to about 5% of the total Bi atoms. BiGa do not account for the modifications in the spectra previously attributed to short range ordering.
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61.72.J- Point defects and defect clusters
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.70.Dm X-ray absorption spectra
81.05.Ea III-V semiconductors

Pyramidal inversion domain boundaries revisited

T. Remmele, M. Albrecht, K. Irmscher, R. Fornari, and M. Straßburg

Appl. Phys. Lett. 99, 141913 (2011); http://dx.doi.org/10.1063/1.3644132 (3 pages)

Online Publication Date: 6 October 2011

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The structure of pyramidal inversion domain boundaries in GaN:Mg was investigated by aberration corrected transmission electron microscopy. The analysis shows the upper (0001) boundary to consist of a single Mg layer inserted between polarity inverted GaN layers in an abcab stacking. The Mg bound in these defects is at least one order of magnitude lower than the chemical Mg concentration. Temperature dependent Hall effect measurements show that up to 27% of the Mg acceptors is electrically compensated.
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61.72.Mm Grain and twin boundaries
72.20.My Galvanomagnetic and other magnetotransport effects
81.05.Ea III-V semiconductors
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
61.72.jd Vacancies

Strong suppression of internal electric field in GaN/AlGaN multi-layer quantum dots in nanowires

R. Songmuang, D. Kalita, P. Sinha, M. den Hertog, R. André, T. Ben, D. González, H. Mariette, and E. Monroy

Appl. Phys. Lett. 99, 141914 (2011); http://dx.doi.org/10.1063/1.3646389 (3 pages) | Cited 3 times

Online Publication Date: 6 October 2011

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Photoluminescence (PL) studies of GaN/AlxGa1−xN quantum dots (QDs) in nanowires demonstrate an efficient carrier confinement, resulting in thermally stable decay times up to 300 K. The evolution of the PL transition energy as a function of both the QD height and the Al mole fraction in the barriers, as well as the evolution of the decay time as a function of the QD height, point out that a built-in electric field is significantly smaller than the value expected from the spontaneous polarization discontinuity. This is explained by the uniaxial compressive strain resulting from the spontaneously formed Al-rich shell that envelops the QD stack.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors

High-pressure phase transformations in MgO-Y2O3 nanocomposites

E. K. Akdoğan, İ. Şavklıyıldız, B. Berke, Z. Zhong, L. Wang, M. Vaughan, and T. Tsakalakos

Appl. Phys. Lett. 99, 141915 (2011); http://dx.doi.org/10.1063/1.3646546 (3 pages) | Cited 1 time

Online Publication Date: 6 October 2011

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Temperature and pressure dependence of phase evolution in 0.5 MgO-0.5 Y2O3 is studied using the diamond anvil method. At 300 K and 5.5 GPa, transformations in Y2O3 are observed, resulting in co-existence of cubic, hexagonal, and monoclinic phases. Heating to 1293 K results in increased crystallinity and increase in hexagonal and monoclinic phase content. Isothermal and isobaric hold at 1273 K and 5.5 GPa for 120 min results in yttrium dissolution in cubic MgO, causing 0.83% volumetric strain. Cooling to 300 K and 0 GPa yields a four phase co-existence among cubic MgO and cubic, hexagonal, and monoclinic Y2O3. The residual MgO unit cell volume expansion is 0.67% at 300 K, indicating solid solution formation. Aging of the nanocomposites for 240 h does not change the observed 4 phase co-existence.
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62.50.-p High-pressure effects in solids and liquids
64.70.Nd Structural transitions in nanoscale materials
81.40.Gh Other heat and thermomechanical treatments
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
64.70.K- Solid-solid transitions

On the strain in n-type GaN

Jinqiao Xie, Seiji Mita, Lindsay Hussey, Anthony Rice, James Tweedie, James LeBeau, Ramón Collazo, and Zlatko Sitar

Appl. Phys. Lett. 99, 141916 (2011); http://dx.doi.org/10.1063/1.3647772 (3 pages) | Cited 5 times

Online Publication Date: 7 October 2011

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It was demonstrated that Ge has the same effect as Si on the strain evolution in n-type GaN as measured by x-ray diffraction. Dislocation inclination, which causes tensile strain in n-type GaN, was clearly observed by transmission electron microscopy where Ge doping was introduced during epitaxial growth. This result is explained by the Fermi level effect model that indicates dislocation inclination due to the climbing process through Ga vacancies. Therefore, there is no dependence of dislocation inclination on dopant species.
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81.40.Lm Deformation, plasticity, and creep
61.72.jd Vacancies
61.72.uj III-V and II-VI semiconductors
62.20.F- Deformation and plasticity
61.72.Lk Linear defects: dislocations, disclinations
81.05.Ea III-V semiconductors

Wurtzite ZnO (001) films grown on cubic MgO (001) with bulk-like opto-electronic properties

Hua Zhou, Hui-Qiong Wang, Lijun Wu, Lihua Zhang, Kim Kisslinger, Yimei Zhu, Xiaohang Chen, Huahan Zhan, and Junyong Kang

Appl. Phys. Lett. 99, 141917 (2011); http://dx.doi.org/10.1063/1.3647846 (3 pages) | Cited 4 times

Online Publication Date: 7 October 2011

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We report the growth of ZnO (001) wurtzite thin films with bulk-like opto-electronic properties on MgO (001) cubic substrates using plasma-assisted molecular beam epitaxy. In situ reflection high-energy electron diffraction patterns and ex situ high resolution transmission electron microscopy images indicate that the structure transition from the cubic MgO substrates to the hexagonal films involves 6 ZnO variants that have the same structure but different orientations. This work demonstrates the possibility of integrating wurtzite ZnO films and functional cubic substrates while maintaining their bulk-like properties.
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78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.kg Semiconductors
68.37.Og High-resolution transmission electron microscopy (HRTEM)
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Insight into unusual impurity absorbability of GeO2 in GeO2/Ge stacks

Shingo Ogawa, Taichi Suda, Takashi Yamamoto, Katsuhiro Kutsuki, Iori Hideshima, Takuji Hosoi, Takayoshi Shimura, and Heiji Watanabe

Appl. Phys. Lett. 99, 142101 (2011); http://dx.doi.org/10.1063/1.3644393 (3 pages) | Cited 3 times

Online Publication Date: 3 October 2011

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Adsorbed species and its diffusion behaviors in GeO2/Ge stacks, which are future alternative metal-oxide-semiconductor (MOS) materials, have been investigated using various physical analyses. We clarified that GeO2 rapidly absorbs moisture in air just after its exposure. After the absorbed moisture in GeO2 reaches a certain limit, the GeO2 starts to absorb some organic molecules, which is accompanied by a structural change in GeO2 to form a partial carbonate or hydroxide. We also found that the hydrogen distribution in GeO2 shows intrinsic characteristics, indicative of different diffusion behaviors at the surface and at the GeO2/Ge interface. Because the impurity absorbability of GeO2 has a great influence on the electrical properties in Ge-MOS devices, these results provide valuable information in realizing high quality GeO2/Ge stacks for the actual use of Ge-MOS technologies.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
68.43.Jk Diffusion of adsorbates, kinetics of coarsening and aggregation
68.43.Mn Adsorption kinetics

Soft x-ray emission spectroscopy studies of the electronic structure of silicon supersaturated with sulfur

J. T. Sullivan, R. G. Wilks, M. T. Winkler, L. Weinhardt, D. Recht, A. J. Said, B. K. Newman, Y. Zhang, M. Blum, S. Krause, W. L. Yang, C. Heske, M. J. Aziz, M. Bär, and T. Buonassisi

Appl. Phys. Lett. 99, 142102 (2011); http://dx.doi.org/10.1063/1.3643050 (3 pages) | Cited 2 times

Online Publication Date: 3 October 2011

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We apply soft x-ray emission spectroscopy (XES) to measure the electronic structure of crystalline silicon supersaturated with sulfur (up to 0.7 at. %), a candidate intermediate-band solar cell material. Si L2,3 emission features are observed above the conventional Si valence band maximum, with intensity scaling linearly with S concentration. The lineshape of the S-induced features change across the insulator-to-metal transition, indicating a significant modification of the local electronic structure concurrent with the change in macroscopic electronic behavior. The relationship between the Si L2,3 XES spectral features and the anomalously high sub-band gap infrared absorption is discussed.
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78.70.En X-ray emission spectra and fluorescence
78.30.Am Elemental semiconductors and insulators
71.20.Mq Elemental semiconductors

Origin of the electrical instabilities in GaN/AlGaN double-barrier structure

S. Sakr, E. Warde, M. Tchernycheva, L. Rigutti, N. Isac, and F. H. Julien

Appl. Phys. Lett. 99, 142103 (2011); http://dx.doi.org/10.1063/1.3645011 (3 pages) | Cited 6 times

Online Publication Date: 3 October 2011

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The effect of the temperature on the electrical characteristics in GaN-based resonant tunneling diodes is studied both theoretically and experimentally. At room temperature, the current-voltage measurements show reproducible negative differential resistances and a current hysteresis. However these features disappear when the temperature is decreased down to 100 K. In addition, the current exhibits transients over a few tenths of seconds which effect disappears at low temperatures. Based on these results, we conclude that the observed negative differential resistance at room temperature is not due to electron resonant tunneling but to trap charging and release.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.30.Kk Junction diodes

Molecular orbital ordering in titania and the associated semiconducting behavior

Joseph Park, Kyung-Chul Ok, Byung Du Ahn, Je Hun Lee, Jae-Woo Park, Kwun-Bum Chung, and Jin-Seong Park

Appl. Phys. Lett. 99, 142104 (2011); http://dx.doi.org/10.1063/1.3646105 (3 pages) | Cited 5 times

Online Publication Date: 3 October 2011

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RF-sputtered TiOx layers were thermally treated and the associated thin-film transistor properties were studied. X-ray diffraction and x-ray absorption spectroscopy analyses indicate that as-grown amorphous TiOx films crystallize to anatase at temperatures above 450 °C in air. Thin-film transistors incorporating anatase active layers exhibit n-type behavior, with field effect mobility values near 0.11 cm2/Vs when annealed at 550 °C. Such a phenomenon is suggested to originate from the ordering of Ti 3d orbitals upon crystallization, and the mobility enhancement at higher annealing temperatures may be attributed to the reduced grain boundary scattering of carriers by virtue of enlarged average grain size.
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68.55.ag Semiconductors
78.70.Dm X-ray absorption spectra
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
61.72.Mm Grain and twin boundaries
81.15.Cd Deposition by sputtering
85.30.Tv Field effect devices

Behavior of nitrogen atoms in SiC-SiO2 interfaces studied by electrically detected magnetic resonance

T. Umeda, K. Esaki, R. Kosugi, K. Fukuda, T. Ohshima, N. Morishita, and J. Isoya

Appl. Phys. Lett. 99, 142105 (2011); http://dx.doi.org/10.1063/1.3644156 (3 pages) | Cited 4 times

Online Publication Date: 4 October 2011

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The microscopic behavior of nitrogen atoms in the SiO2-SiC interface regions of n-channel lateral 4 H-SiC metal-oxide-semiconductor field effect transistors (MOSFETs) was studied using low-temperature electrically detected magnetic resonance spectroscopy and other techniques. The results show that nitrogen atoms eliminated shallow interface states observable at 20 K and further diffused into the channel region of the MOSFETs as shallow donors. These two behaviors enable nitrogen atoms to change the channel conductivity of SiC MOSFETs.
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73.20.At Surface states, band structure, electron density of states
85.30.Tv Field effect devices

Long hold times in a two-junction electron trap

A. Kemppinen, S. V. Lotkhov, O.-P. Saira, A. B. Zorin, J. P. Pekola, and A. J. Manninen

Appl. Phys. Lett. 99, 142106 (2011); http://dx.doi.org/10.1063/1.3647557 (3 pages) | Cited 3 times

Online Publication Date: 5 October 2011

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The hold time τ of a single-electron trap is shown to increase significantly due to suppression of photon assisted tunneling events. Using two rf-tight radiation shields instead of a single one, we demonstrate increase of τ by a factor exceeding 103, up to about 10 h, for a trap with only two superconductor (S)—normal-metal (N) tunnel junctions and an on-chip resistor R ∼ 100 kΩ (R-SNS structure). In the normal state, the improved shielding made it possible to observe τ ∼ 100 s, which is in reasonable agreement with the quantum-leakage-limited level expected for the two-electron cotunneling process.
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85.25.Cp Josephson devices
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.55.+v Tunneling phenomena: single particle tunneling and STM
84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)

Effect of temperature on CO detection sensitivity of ZnO nanorod-gated AlGaN/GaN high electron mobility transistors

Chien-Fong Lo, B. H. Chu, S. J. Pearton, A. Dabiran, P. P. Chow, S. Doré, S. C. Hung, C. W. Chen, and F. Ren

Appl. Phys. Lett. 99, 142107 (2011); http://dx.doi.org/10.1063/1.3647561 (3 pages) | Cited 1 time

Online Publication Date: 5 October 2011

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The carbon monoxide (CO) detection sensitivities of ZnO nanorod-gated AlGaN/GaN high electron mobility transistors were measured over a range of temperatures from 25–150 °C. Once the sensor was exposed to the CO-containing ambient, the drain current, I, of the high electron mobility transistors increased due to chemisorbed oxygen on the ZnO surface reacting with CO, forming CO2 and releasing electrons to the oxide surface. Although the sensor could detect CO as low as 100 ppm at room temperature, the detection sensitivity, ΔI/I, was only around 0.23%. By increasing the sensor temperature to 150 °C, the detection sensitivity was improved by a factor of over 30% to 7.5%.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.-d Chemical analysis and related physical methods of analysis
85.30.Tv Field effect devices

Highly strained-SiGe-on-insulator p-channel metal-oxide-semiconductor field-effective transistors fabricated by applying Ge condensation technique to strained-Si-on-insulator substrates

Junkyo Suh, Ryosho Nakane, Noriyuki Taoka, Mitsuru Takenaka, and Shinichi Takagi

Appl. Phys. Lett. 99, 142108 (2011); http://dx.doi.org/10.1063/1.3647631 (3 pages) | Cited 3 times

Online Publication Date: 5 October 2011

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High hole mobility enhancement of strained SiGe-on-insulator (sSGOI) p-channel metal-oxide-semiconductor field-effect transistors (pMOSFETs) has been achieved by utilizing strained-SOI (sSOI) substrates in Ge condensation. The initial tensile strain in the sSOI substrates alleviates strain relaxation during Ge condensation process, because of smaller lattice mismatch to Ge than conventional unstrained SOI substrates. In addition, generation of hole carrier concentration and degradation of bottom interface are suppressed. Mitigation in strain relaxation is shown to effectively increase strain in SGOI layers and resulting hole mobility in the SGOI pMOSFETs in high Ge content region. The observed high mobility enhancement can be quantitatively explained by the combination of high Ge content and a large amount of compressive strain, through comparison of experimental data with theoretical calculations.
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85.30.Tv Field effect devices

Prediction of the chemical trends of oxygen vacancy levels in binary metal oxides

Wan-Jian Yin, Su-Huai Wei, Mowafak M. Al-Jassim, and Yanfa Yan

Appl. Phys. Lett. 99, 142109 (2011); http://dx.doi.org/10.1063/1.3647756 (3 pages) | Cited 2 times

Online Publication Date: 5 October 2011

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We propose simple principles to predict qualitatively the chemical trends of oxygen vacancy levels in binary metal oxides by analyzing the atomic wavefunction characters of the conduction-band minimum (CBM). We show that if the CBM is a metal-oxygen antibonding state due to either s-s coupling, p-p coupling, or p-d coupling, then, in general, the oxygen vacancy level is deep. The stronger coupling leads to deeper levels. If the CBM is a non-bonding d state, then the oxygen vacancy level could be shallow. These principles are confirmed by the calculated trends of oxygen vacancy levels in representative binary metal oxides using hybrid density-functional method.
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61.72.jd Vacancies
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.55.Ht Other nonmetals

Flexible resistive random access memory using solution-processed TiOx with Al top electrode on Ag layer-inserted indium-zinc-tin-oxide-coated polyethersulfone substrate

Seungjae Jung, Jaemin Kong, Sunghoon Song, Kwanghee Lee, Takhee Lee, Hyunsang Hwang, and Sanghun Jeon

Appl. Phys. Lett. 99, 142110 (2011); http://dx.doi.org/10.1063/1.3621826 (3 pages) | Cited 2 times

Online Publication Date: 5 October 2011

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We demonstrated a flexible resistive random access memory (FReRAM) device using a solution-processed TiOx active layer with an Al top electrode on an Ag layer-inserted indium-zinc-tin-oxide (IAI)-coated polyethersulfone substrate (Al/TiOx/IAI). Its feasibility of FReRAM application was evaluated through the comparison of electrical and mechanical characteristics with devices having different structure such as Ag/TiOx/Ag, Al/TiOx/indium-tin-oxide, and Al/TiOx/Al. As a result, our FReRAM device exhibited greater FReRAM performance such as stable memory characteristics under mechanically bent conditions and robustness to repetitive bending cycles. In addition, the device was thermally stable up to 85 °C, despite its flexible electrode and polymer substrate.
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84.30.Sk Pulse and digital circuits

Oxygen-enhanced wet thermal oxidation of GaAs

J. F. Bauters, R. E. Fenlon, C. S. Seibert, W. Yuan, J. S. B. Plunkett, J. Li, and D. C. Hall

Appl. Phys. Lett. 99, 142111 (2011); http://dx.doi.org/10.1063/1.3647579 (3 pages) | Cited 1 time

Online Publication Date: 6 October 2011

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An oxygen-enhanced wet thermal oxidation process is used to grow smooth, uniform, insulating native oxides of GaAs. At 420 °C, a maximum linear growth rate of 4.8 nm/min is observed for oxidation in water vapor with 2000 ppm O2 added relative to the N2 carrier gas, with growth ceasing by 7000 ppm. Films as thick as 800 nm with surface roughness as low as 0.2 nm are demonstrated. In fabricated metal-oxide-semiconductor capacitors, a 412 nm thick native oxide film exhibits a factor of ∼2700 reduction in leakage current density at 1 V relative to a direct metal (Au:Ti) to GaAs contact.
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81.65.Mq Oxidation
84.32.Tt Capacitors
85.30.Tv Field effect devices
68.35.bg Semiconductors
68.55.ag Semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Experimental observation of an enhanced anisotropic magnetoresistance in non-local configuration

D. Rüffer, F. D. Czeschka, R. Gross, and S. T. B. Goennenwein

Appl. Phys. Lett. 99, 142112 (2011); http://dx.doi.org/10.1063/1.3640487 (3 pages)

Online Publication Date: 6 October 2011

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We compare non-local magnetoresistance measurements in multi-terminal Ni nanostructures with corresponding local experiments. In both configurations, the measured voltages show the characteristic features of anisotropic magnetoresistance (AMR). However, the magnitude of the non-local AMR signal is up to one order of magnitude larger than its local counterpart. Moreover, the non-local AMR increases with increasing degree of non-locality, i.e., with the separation between the region of the main current flow and the voltage measurement region. All experimental observations can be consistently modeled in terms of current spreading in a non-isotropic conductor. Our results show that current spreading can significantly enhance the magnetoresistance signal in non-local experiments.
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75.75.-c Magnetic properties of nanostructures
75.47.Np Metals and alloys
75.50.Cc Other ferromagnetic metals and alloys
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