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1 May 2012

Volume 111, Issue 9, Articles (09xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 111, 093103 (2012); http://dx.doi.org/10.1063/1.4709385 (8 pages)

Ani Khachatrian, Joseph S. Melinger, and Syed B. Qadri
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back to top Electronic Structure and Transport

Thermophysical and electrical properties of Al-doped ZnO films

Nobuto Oka, Kentaro Kimura, Takashi Yagi, Naoyuki Taketoshi, Tetsuya Baba, and Yuzo Shigesato

J. Appl. Phys. 111, 093701 (2012); http://dx.doi.org/10.1063/1.4706572 (5 pages) | Cited 3 times

Online Publication Date: 1 May 2012

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Thermal diffusivity of Al-doped ZnO (AZO) films with a thickness of 200 nm was quantitatively analyzed using a “rear heating/front detection type” nanosecond thermoreflectance system. AZO monolayer and Mo/AZO/Mo three-layered films were prepared on synthesized silica substrates by DC magnetron sputtering using high density ceramic ZnO–Al2O3 (Al2O3: 2.5 wt. %) and Mo metal targets. The thermal diffusivity and electrical resistivity of the deposited AZO films ranged 1.8 × 10−6 –2.4 × 10−6 m2 s−1 and 2.3 × 10−3–5.9 × 10−4 Ω cm, respectively. The thermal conductivity corresponding to the thermal diffusivity was one order of magnitude smaller than that of sintered AZO ceramics prepared from ZnO and Al2O3 powders. However, it was found to be larger than that of In2O3-based transparent conductive oxide (TCO) films with approximately the same electrical conductivity, thus implying that AZO can be considered an excellent material for diathermanous TCO circuits.
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66.70.Df Metals, alloys, and semiconductors
68.55.ag Semiconductors
78.20.N- Thermo-optic effects
81.15.Cd Deposition by sputtering

Enhanced spin figure of merit in a Rashba quantum dot ring connected to ferromagnetic leads

Jun Zheng and Feng Chi

J. Appl. Phys. 111, 093702 (2012); http://dx.doi.org/10.1063/1.4707934 (6 pages) | Cited 1 time

Online Publication Date: 1 May 2012

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Spin-dependent thermoelectric effect is studied in an Aharonov-Bohm ring with a quantum dot (QD) inserted in one of its arms. We consider that the ring is connected to external ferromagnetic electrodes and there exists Rashba spin-orbit (RSO) interaction in the QD. The spin thermopower Ss and the spin figure of merit ZsT are calculated in terms of the Keldysh Green’s function method. We found that the ZsT value can be significantly enhanced by the coaction of the ferromagnetism of the leads and the RSO interaction. By optimizing the structure parameters, the value of ZsT can be up to 1 at room temperature. In addition, pure spin-up (spin-down) thermopower (or Seebeck coefficient) can be generated with high ZsT values. Our results indicate that such a single dot ring may be used as a high efficiency spin thermoelectric generator.
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73.21.La Quantum dots
73.23.-b Electronic transport in mesoscopic systems
82.45.Fk Electrodes
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
72.20.Pa Thermoelectric and thermomagnetic effects

Field dependence of the E1′ and M3′ electron traps in inductively coupled Ar plasma treated n-Gallium Arsenide

A. Venter, C. Nyamhere, J. R. Botha, F. D. Auret, S. M. M. Coelho, and W. E. Meyer

J. Appl. Phys. 111, 093703 (2012); http://dx.doi.org/10.1063/1.4709390 (5 pages)

Online Publication Date: 1 May 2012

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Inductively coupled Ar plasma etching of n-type (Si doped) Gallium Arsenide (GaAs) introduces several electron traps, Ec – 0.04 eV (labelled E1′), Ec – 0.19 eV, Ec – 0.31 eV, Ec – 0.53 eV, and Ec – 0.61 eV (behaving like the well documented M3 and labelled M3′ in this study), of which the metastable defects Ec – 0.04 eV (E1′), and Ec – 0.07 eV are novel. Furthermore, E1′ and M3′ exhibit strong field enhanced carrier emission. Double-correlation deep level transient spectroscopy was used to investigate the field dependent emission behaviour of these two defects. It is shown that for both traps, the observed enhanced emission is due to phonon assisted tunnelling. The latter observation is contrary to the literature reports suggesting that enhanced carrier emission for M3 occurs via the Poole-Frenkel mechanism.
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79.70.+q Field emission, ionization, evaporation, and desorption
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
71.55.Eq III-V semiconductors

Surface properties of stoichiometric and defect-rich indium oxide films grown by MOCVD

M. Himmerlich, Ch. Y. Wang, V. Cimalla, O. Ambacher, and S. Krischok

J. Appl. Phys. 111, 093704 (2012); http://dx.doi.org/10.1063/1.4704700 (6 pages) | Cited 1 time

Online Publication Date: 2 May 2012

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The influence of metalorganic chemical vapor deposition growth conditions on the indium oxide surface properties is investigated using photoelectron spectroscopy. Particular attention is paid to nanocrystalline samples grown at fairly low temperatures which are known for their high sensitivity to ozone. The results are compared to measurements on In2O3 films in cubic and rhombohedral crystal structure. It is shown that the growth conditions have a strong impact on the physical properties and that samples grown at 200 °C or below are highly oxygen-deficient and rich in defects, influencing the surface chemical and electronic properties and resulting in high ozone sensitivity.
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68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
79.60.Bm Clean metal, semiconductor, and insulator surfaces
61.46.-w Structure of nanoscale materials
73.20.At Surface states, band structure, electron density of states
81.16.-c Methods of micro- and nanofabrication and processing

Electric field tuning of spin splitting in a quantum dot coupled to a semimagnetic quantum dot

Y. Lyanda-Geller, T. L. Reinecke, and G. Bacher

J. Appl. Phys. 111, 093705 (2012); http://dx.doi.org/10.1063/1.4705287 (5 pages)

Online Publication Date: 3 May 2012

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We develop an approach for tuning the spin splitting and g-factor of a quantum dot by coupling it to semi-magnetic quantum dot and tuning the electric field. We show that spin splittings and g-factors of the states of a non-magnetic quantum dot coupled to semimagnetic quantum dot can be enhanced orders of magnitude. Evaluations are made for coupled CdTe/CdMnTe quantum dots. These effects are caused by electric field control of repulsion of spin sublevels in the non-magnetic dot due to tunnel coupling of quantum dots. Electric field control of spin splittings in quantum dots is of potential interest in connection with spin qubit rotations for quantum computation.
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71.70.-d Level splitting and interactions
73.61.Ga II-VI semiconductors
73.63.Kv Quantum dots
75.50.Pp Magnetic semiconductors
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
03.67.Lx Quantum computation architectures and implementations

Synthesis and evolution of magnetic properties of Ni doped La2/3Sr1/3Mn1−xNixO3 nanoparticles

Maneesha Gupta, Wasi Khan, Poonam Yadav, R. K. Kotnala, A. Azam, and A. H. Naqvi

J. Appl. Phys. 111, 093706 (2012); http://dx.doi.org/10.1063/1.4707757 (6 pages) | Cited 2 times

Online Publication Date: 3 May 2012

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A systematic investigation of the structural and magnetic properties of La2/3Sr1/3Mn1−xNixO3 (x = 0%, 5%, 15%, and 25%) perovskite nanoparticles synthesized using mild sol-gel technique is reported. These samples were characterized using x-ray diffraction (XRD), transmission electron microscopy, Fourier transform infrared (FTIR) spectroscopy, and temperature dependent magnetoresistance (MR) measurements. XRD analysis confirmed the single phase nature of the samples, and crystallite size was found to decrease from 21.4 nm to 17.0 nm with the increase in Ni concentration. Further, maximum MR was observed for 25% Ni doped sample at low temperature (77 K), whereas at room temperature (300 K) MR decreases with increase in Ni concentration. FTIR spectra show a broad peak at 605.28 cm−1, giving an evidence for the formation of metal oxygen bond which subsequently organize into a MnO6 octahedral structure as evidenced by the appearance of a well defined spectral band. Room temperature magnetization for all samples reduces with Ni doping and it is highest for 5% doped sample. The results have been explained on the basis of destruction of the partial double-exchange interactions and the exchange couplings between Mn and doped ions.
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75.75.Cd Fabrication of magnetic nanostructures
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
72.20.My Galvanomagnetic and other magnetotransport effects
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.16.Be Chemical synthesis methods

Spin accumulation in a multi-arm Aharonov-Bohm-Fano interferometer

Wei-Jiang Gong, Yu Han, Francis N. Kariuki, and An Du

J. Appl. Phys. 111, 093707 (2012); http://dx.doi.org/10.1063/1.4709623 (5 pages)

Online Publication Date: 3 May 2012

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The spin accumulation properties of a multi-arm Aharonov-Bohm-Fano interferometer are investigated by considering spin bias in the leads. We find that the spin accumulations in the quantum dots (QDs) can be adjusted independently by changing the magnetic fluxes through the sub-rings formed by the QD-lead and lead-lead couplings. When analyzing the quantum interference effect, we find that the Aharonov-Bohm-Fano interference mechanism is a necessary condition to realize the spin accumulation. Based on the numerical results, we propose that such a structure has a significant potential as a candidate for a spin-manipulating device.
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73.21.La Quantum dots
73.23.-b Electronic transport in mesoscopic systems
75.30.Ds Spin waves

Thermal conductivity of bulk and thin-film silicon: A Landauer approach

Changwook Jeong, Supriyo Datta, and Mark Lundstrom

J. Appl. Phys. 111, 093708 (2012); http://dx.doi.org/10.1063/1.4710993 (6 pages) | Cited 3 times

Online Publication Date: 3 May 2012

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The question of what fraction of the total heat flow is transported by phonons with different mean-free-paths is addressed using a Landauer approach with a full dispersion description of phonons to evaluate the thermal conductivities of bulk and thin film silicon. For bulk Si, the results reproduce those of a recent molecular dynamic treatment showing that about 50% of the heat conduction is carried by phonons with a mean-free-path greater than about 1 μm. For the in-plane thermal conductivity of thin Si films, we find that about 50% of the heat is carried by phonons with mean-free-paths shorter than in the bulk. When the film thickness is smaller than ∼0.2 μm, 50% of the heat is carried by phonons with mean-free-paths longer than the film thickness. The cross-plane thermal conductivity of thin-films, where quasi-ballistic phonon transport becomes important, is also examined. For ballistic transport, the results reduce to the well-known Casimir limit [H. B. G. Casimir, Physica 5, 495–500 (1938)]. These results shed light on phonon transport in bulk and thin-film silicon and demonstrate that the Landauer approach provides a relatively simple but accurate technique to treat phonon transport from the ballistic to diffusive regimes.
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66.70.Df Metals, alloys, and semiconductors
66.30.Xj Thermal diffusivity
73.23.Ad Ballistic transport
63.22.Dc Free films

Direct hole and delayed electron capture on a picosecond timescale by Eu2+ centers in CaGa2S4 monitored by synchroscan with horizontal blanking

D. J. Louwers, T. Takizawa, C. Hidaka, and E. van der Kolk

J. Appl. Phys. 111, 093709 (2012); http://dx.doi.org/10.1063/1.4709757 (7 pages)

Online Publication Date: 4 May 2012

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A Eu2+ concentration and temperature dependent energy transfer study from the host lattice to Eu2+ luminescence centers in Ca(1–x)EuxGa2S4 (x = 0.001 to 0.05) was performed with a special streak camera that combines the high timing resolution of a conventional synchroscan operation (<2 ps) with the ability to study long lived states (10 ns − 1 ms) typical for rare earth and transition metal ions. Two transfer mechanisms from the CaGa2S4 host lattice to the Eu2+ ions were identified. A fast transfer process (<4 ps) is interpreted as sequential hole-electron capture by the Eu2+ ions, and slower process (>1 ns) is interpreted as the sequential capture of a hole and an electron by Eu2+ but with the electron first entering an intermediate state trapped near Eu3+. Energy transfer via a self-trapped excitonic (STE) state is unlikely because of the absence of an anti-correlation between the STE decay-time and the Eu2+ rise-time as well as between the STE emission intensity and the Eu2+ intensity. All rise-time spectra were successfully fitted with a model representing the above transfer mechanisms.
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78.47.J- Ultrafast spectroscopy (<1 psec)
71.35.Ee Electron-hole drops and electron-hole plasma
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Sk Insulators
78.55.Hx Other solid inorganic materials

Thermoelectric properties of tungsten-substituted Heusler Fe2VAl alloy

M. Mikami, Y. Kinemuchi, K. Ozaki, Y. Terazawa, and T. Takeuchi

J. Appl. Phys. 111, 093710 (2012); http://dx.doi.org/10.1063/1.4710990 (6 pages) | Cited 2 times

Online Publication Date: 4 May 2012

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A Heusler Fe2V1-xWxAl sintered alloy was synthesized to evaluate the effect of W substitution on thermoelectric properties of the Heusler alloy. The Seebeck coefficient and the electrical conductivity are simultaneously enhanced through electron injection resulting from the W substitution. Comparison with the Si-substituted Fe2VAl alloy reveals that the additional electronic states derived from W 5d orbital in the vicinity of pseudogap are likely to degrade the Seebeck coefficient. Thermal conductivity is effectively reduced by the W substitution because of the large atomic mass and volume of W compared to the constituent elements of Fe2VAl alloy. The appreciable reduction of thermal conductivity, without a serious deterioration in electrical conduction, enhances the thermoelectric figure of merit in the Heusler alloy.
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72.15.Jf Thermoelectric and thermomagnetic effects
72.80.Sk Insulators
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys

Cyclotron resonance study in InAs/AlSb quantum well heterostructures with two occupied electronic subbands

S. S. Krishtopenko, A. V. Ikonnikov, A. V. Maremyanin, K. E. Spirin, V. I. Gavrilenko, Yu. G. Sadofyev, M. Goiran, M. Sadowsky, and Yu. B. Vasilyev

J. Appl. Phys. 111, 093711 (2012); http://dx.doi.org/10.1063/1.4712042 (7 pages) | Cited 2 times

Online Publication Date: 7 May 2012

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We report on the cyclotron resonance (CR) study in InAs/AlSb (001) quantum well (QW) heterostructures with two occupied electronic subbands. Experimental results are compared with the CR energy calculations in the self-consistent Hartree approximation. Our theoretical approach is based on the 8-band k · p Hamiltonian and takes into account the band nonparabolicity, lattice-mismatch deformation, and spin-orbit coupling. We find out a large splitting of CR line associated with a difference in cyclotron energies in the first and second electronic subbands. The results of CR study in InAs/AlSb QW heterostructures reveal pronounced effect of the “built-in” electric field on CR spectra in the samples with two occupied electronic subbands.
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76.40.+b Diamagnetic and cyclotron resonances
71.20.Nr Semiconductor compounds
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
73.21.Fg Quantum wells
73.63.Hs Quantum wells

Excitation-dependent recombination and diffusion near an isolated dislocation in GaAs

T. H. Gfroerer, C. M. Crowley, C. M. Read, and M. W. Wanlass

J. Appl. Phys. 111, 093712 (2012); http://dx.doi.org/10.1063/1.4709434 (4 pages) | Cited 1 time

Online Publication Date: 7 May 2012

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In low-magnification, plan-view photoluminescence images of a nominally lattice-matched, undoped GaAs/GaInP heterostructure, we observe a random distribution of isolated dark spots. We attribute the dark spots to crystal dislocations, where nonradiative recombination is augmented by transitions utilizing defect-related energy levels between the conduction and valence bands. We note that, when the laser excitation intensity is reduced, the darkened regions expand. At lower excitation, the density of photogenerated electrons and holes is reduced, and they are more likely to reach the defective region before encountering a partner for radiative recombination. When we model the behavior with a simulation that allows for Laplacian diffusion and defect-related recombination only through mid-bandgap energy levels, we do not obtain good agreement between experimental and simulated images. But if we allow for an arbitrary distribution of defect levels, such that the occupation of the levels and bands can change independently, we have more flexibility for fitting the density-dependent recombination rates. The more sophisticated model produces results that are more consistent with experimental images.
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71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
66.30.-h Diffusion in solids
71.20.Nr Semiconductor compounds

Influence of annealing and Al2O3 properties on the hydrogen-induced passivation of the Si/SiO2 interface

G. Dingemans, F. Einsele, W. Beyer, M. C. M. van de Sanden, and W. M. M. Kessels

J. Appl. Phys. 111, 093713 (2012); http://dx.doi.org/10.1063/1.4709729 (9 pages) | Cited 4 times

Online Publication Date: 7 May 2012

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Annealing at moderate temperatures is required to activate the silicon surface passivation by Al2O3 thin films while also the thermal stability at higher temperatures is important when Al2O3 is implemented in solar cells with screenprinted metallization. In this paper, the relationship between the microstructure of the Al2O3 film, hydrogen diffusion, and defect passivation is explored in detail for a wide range of annealing temperatures. The chemical passivation was studied using stacks of thermally-grown SiO2 and Al2O3 synthesized by atomic layer deposition. Thermal effusion measurements of hydrogen and implanted He and Ne atoms were used to elucidate the role of hydrogen during annealing. We show that the passivation properties were strongly dependent on the annealing temperature and time and were significantly influenced by the Al2O3 microstructure. The latter was tailored by variation of the deposition temperature (Tdep = 50 °C–400 °C) with hydrogen concentration [H] between 1 and 13 at.% and mass density ρmass between 2.7 and 3.2 g/cm3. In contrast to films with intermediate material properties, the passivation by low- and high density films showed a reduced thermal stability at relatively high annealing temperatures (∼600 °C). These observations proved to be in good agreement with thermal effusion results of hydrogen and inert gas atoms that were also strongly dependent on film microstructure. We demonstrate that the temperature of maximum effusion decreased for films with progressively lower density (i.e., with increasing [H]). Therefore, the reduced thermal stability of the passivation for low-density hydrogen-rich ([H] >∼5 at. %) films can be attributed to a loss of hydrogen at relatively low annealing temperatures. In contrast, the lower initial [H] for dense Al2O3 films can likely explain the lower thermal stability associated with these films. The effusion measurements also allowed us to discuss the role of molecular- and atomic hydrogen during annealing.
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81.40.Gh Other heat and thermomechanical treatments
81.65.Rv Passivation
66.30.-h Diffusion in solids
68.55.-a Thin film structure and morphology
68.60.Dv Thermal stability; thermal effects

Effect of defect bands in β-In2S3 thin films

R. Jayakrishnan, Tina Sebastian, C. Sudha kartha, and K. P. Vijayakumar

J. Appl. Phys. 111, 093714 (2012); http://dx.doi.org/10.1063/1.4709767 (6 pages) | Cited 1 time

Online Publication Date: 7 May 2012

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Optical absorption studies in β-In2S3 thin films of band gap 2.66 eV, prepared using chemical spray pyrolysis technique, revealed presence of a defect band which could assist absorption of sub band gap photons. Extrinsic photoconductivity under excitation of 2.33 eV was observed in these films. Photoluminescence studies revealed a green emission from the films providing a recombination path to these carriers. Temperature dependence of photoconductivity showed that the states in the defect band were continuously exchanging carriers with the conduction band which caused the photocurrent to show persistent photoconductivity. Temperature dependence of photocurrent revealed existence of shallow traps located ∼24 meV below the conduction band which played vital role in controlling the photosensitivity of the films. Temporal dependence of photoconductivity revealed decay tails which were identified to be the effect of thermal release of carriers form the shallow traps.
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71.55.Ht Other nonmetals
72.40.+w Photoconduction and photovoltaic effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.55.Hx Other solid inorganic materials
78.66.Li Other semiconductors
71.20.Nr Semiconductor compounds

Key capacitive parameters for designing single-electron transistor charge sensors

Kosuke Horibe, Tetsuo Kodera, Tomohiro Kambara, Ken Uchida, and Shunri Oda

J. Appl. Phys. 111, 093715 (2012); http://dx.doi.org/10.1063/1.4711094 (5 pages)

Online Publication Date: 7 May 2012

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Single-electron transistors (SETs) are efficient charge sensors for reading out spin or charge qubits confined in quantum dots (QDs). To investigate their capacitive parameters, which are related to the signal-to-noise ratio (SNR) during qubit readout, twin silicon single QDs were fabricated using a lithographic process on a silicon-on-insulator substrate. Since the configuration and dimensions of the QDs could be determined by direct imaging, the theoretical capacitive parameters could be compared to the measured values. Good agreement was found between the calculated and measured values, which confirms the validity of the calculation method. The results indicated that decreasing the SET diameter reduces the capacitive coupling between qubits but increases the signal-to-noise ratio for both dc and radio frequency single-shot measurements. Since these results are independent of the device materials, they are useful for establishing guidelines for the design of SET charge sensors in lateral QD-SET structures based on a two-dimensional electron gas.
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85.35.Gv Single electron devices

Crystal structure and thermoelectric properties of KxBa8−xZnyGe46−y clathrates

Kengo Kishimoto, Yuta Sasaki, Tsuyoshi Koyanagi, Kenji Ohoyama, and Koji Akai

J. Appl. Phys. 111, 093716 (2012); http://dx.doi.org/10.1063/1.4711100 (8 pages) | Cited 1 time

Online Publication Date: 7 May 2012

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Polycrystalline samples of degenerate n-type KxBa8−xZnyGe46−y (y ∼ 8-x/2) with the type-I clathrate structure (No. 223, Pmmathn) were prepared by powder metallurgy to obtain a high-efficiency Ge-based clathrate. Their Zn atoms preferred to exist at the 6c site in the framework, and consequently, the samples with x around 4, such as K4Ba4Zn6Ge40, possessed highly ordered Zn/Ge atom frameworks whose 6c, 16i, and 24k sites were occupied almost solely by Zn, Ge, and Ge atoms, respectively. In spite of such ordered structures and small numbers of substituting Zn atoms, these samples exhibited carrier mobilities lower than those of Ba8Zn8Ge38 and Ba8Ga16Ge30. Band structure calculations implied that the combination of the rattler K and Ba atoms in the cages considerably modified the conduction band edge of the corresponding clathrates; such a modification is considered to strengthen alloy disorder scattering, which reduces carrier mobility. The maximum dimensionless figure-of-merit ZT was 0.51 at 1000 K for the K2Ba6Zn7Ge39 sample, which is similar to that of 0.50 at 900 K for the Ba8Zn8Ge38 sample.
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61.66.Fn Inorganic compounds
72.20.Pa Thermoelectric and thermomagnetic effects
72.20.Fr Low-field transport and mobility; piezoresistance
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
72.80.Jc Other crystalline inorganic semiconductors
71.20.Nr Semiconductor compounds

Gate-controlled spin transport in a spin-diode structure

Yuan Li, Mansoor B. A. Jalil, and Seng Ghee Tan

J. Appl. Phys. 111, 093717 (2012); http://dx.doi.org/10.1063/1.4712027 (5 pages)

Online Publication Date: 8 May 2012

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We investigate the spin transport in a spin-diode structure consisting of a quantum dot (QD) coupled to a ferromagnetic lead and a nonmagnetic (NM) lead. Electron transport through the QD system is investigated theoretically by means of the nonequilibrium Keldysh Green’s function technique. The presence of a spin bias in the NM lead induces a charge current, which shows an asymmetric “spoon-like” current-bias characteristic. The spoon-like profile can be suppressed by tuning the energy level of the QD via the gate voltage. The maximum spin-bias-induced current occurs when the tunnel couplings across the left and the right tunnel barriers are close to each other for spin-up or spin-down electrons. The effect of the tunnel couplings can thus be utilized in the design of spin-diode structures.
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72.25.-b Spin polarized transport
73.40.Gk Tunneling
73.63.Kv Quantum dots
75.50.Cc Other ferromagnetic metals and alloys

Radio-frequency superimposed direct current magnetron sputtered Ga:ZnO transparent conducting thin films

Ajaya K. Sigdel, Paul F. Ndione, John D. Perkins, Thomas Gennett, Maikel F. A. M. van Hest, Sean E. Shaheen, David S. Ginley, and Joseph J. Berry

J. Appl. Phys. 111, 093718 (2012); http://dx.doi.org/10.1063/1.4709753 (7 pages)

Online Publication Date: 8 May 2012

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The utilization of radio-frequency (RF) superimposed direct-current (DC) magnetron sputtering deposition on the properties of gallium doped ZnO (GZO) based transparent conducting oxides has been examined. The GZO films were deposited using 76.2 mm diameter ZnO:Ga2O3 (5 at. % Ga vs. Zn) ceramic oxide target on heated non-alkaline glass substrates by varying total power from 60 W to 120 W in steps of 20 W and at various power ratios of RF to DC changing from 0 to 1 in steps of 0.25. The GZO thin films grown with pure DC, mixed approach, and pure RF resulted in conductivities of 2200 ± 200 S/cm, 3920 ± 600 S/cm, and 3610 ± 400 S/cm, respectively. X-ray diffraction showed all films have wurtzite ZnO structure with the c-axis oriented perpendicular to the substrate. The films grown with increasing RF portion of the total power resulted in the improvement of crystallographic texture with smaller full-width half maximum in χ and broadening of optical gap with increased carrier concentration via more efficient doping. Independent of the total sputtering power, all films grown with 50% or higher RF power portion resulted in high mobility (∼28 ± 1 cm2/Vs), consistent with observed improvements in crystallographic texture. All films showed optical transmittance of ∼90% in the visible range.
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68.55.ag Semiconductors
73.61.Ga II-VI semiconductors
78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors
81.15.Cd Deposition by sputtering
61.72.uj III-V and II-VI semiconductors

Coexistence of free holes and electrons in InN:Mg with In- and N-growth polarities

L. H. Dmowski, M. Baj, L. Konczewicz, T. Suski, D. K. Maude, S. Grzanka, X. Q. Wang, and A. Yoshikawa

J. Appl. Phys. 111, 093719 (2012); http://dx.doi.org/10.1063/1.4710529 (5 pages) | Cited 1 time

Online Publication Date: 9 May 2012

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The coexistence of two types of carriers (free electrons and free holes) in InN:Mg and their competition is demonstrated by the temperature and magnetic-field-induced change of the sign of thermopower (α) as well as the maximum entropy mobility spectrum analysis. The results confirm the existence of alternative carrier channels in addition to the n-type surface inversion layer and p-type bulk. They also show that In-polarity can be propitious for occurrence of p-type conductivity.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Ey III-V and II-VI semiconductors
73.25.+i Surface conductivity and carrier phenomena
72.20.Fr Low-field transport and mobility; piezoresistance

Influence of 3d transition metals on the stability and electronic structure of MgH2

X. Q. Zeng, L. F. Cheng, J. X. Zou, W. J. Ding, H. Y. Tian, and C. Buckley

J. Appl. Phys. 111, 093720 (2012); http://dx.doi.org/10.1063/1.4714549 (10 pages) | Cited 1 time

Online Publication Date: 10 May 2012

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The effect of minor addition of 3d transition metals on the formation enthalpy (△H) and electronic structure of MgH2 have been studied using first-principle calculations, and considering the phonon-calculated zero point energy. The results indicate that the partial substitution of Mg atoms by 3d transition metal atoms increases the formation enthalpy of MgH2. Both formation enthalpy and Mulliken population analysis showed that the ability to destabilize MgH2 generally increases with the atomic number, except Mn and Zn, which have half-filled and completely filled 3d orbital states. The destabilization of MgH2 by partially alloying 3d elements was due to relatively stronger covalent bonds between 3d elements and the H atom, and a weaker ionic bond between Mg and H in the alloyed material with respect to pure MgH2. Based on electronic structure analyses, MgH2 and MgH2 alloyed with Ti, Fe, and Zn show no spin magnetism, while MgH2 alloyed with Sc, V, Cr, Mn, Co, Ni, and Cu show spin magnetism. In the MgH2-3d metal system except Zn, the bonding peak near the Fermi energy is mainly contributed by 3d electrons of transition metals and weak H (s) states. The bonding nature of MgH2 is ionic, and the bonding nature of MgH2-3d metal systems is mainly ionic with covalent bonds between 3d metal atoms and their neighbor H atoms.
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71.20.Ps Other inorganic compounds
82.60.Cx Enthalpies of combustion, reaction, and formation
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
61.50.Lt Crystal binding; cohesive energy

Ultrafast carrier response of Br+-irradiated In0.53Ga0.47As excited at telecommunication wavelengths

L. Fekete, H. Němec, Z. Mics, F. Kadlec, P. Kužel, V. Novák, J. Lorinčík, M. Martin, J. Mangeney, J. C. Delagnes, and P. Mounaix

J. Appl. Phys. 111, 093721 (2012); http://dx.doi.org/10.1063/1.4709441 (8 pages)

Online Publication Date: 10 May 2012

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We present results of infrared pump—terahertz probe experiments applied to a set of In0.53Ga0.47As films irradiated with heavy ions (Br+) at doses from 109 to 1012 cm−2. Photoexcitation at 1400 nm (0.89 eV) allowed us to characterize the response close to telecommunications’ wavelengths whilst avoiding the intervalley carrier scattering observed when a shorter wavelength excitation is used. The excitation fluence was varied in our experiments in order to characterize the dynamics in detail: the lifetimes and mobilities of both electrons and holes were retrieved, and the trap filling and carrier diffusion were clearly observed. The In0.53Ga0.47As film irradiated by the dose of 1012 cm−2 exhibits simultaneously ultrashort electron lifetime (∼300 fs) and very high electron mobility (2800 cm2V−1s−1). These findings are particularly important for the design of terahertz emitters controlled by lasers operating at standard telecommunication wavelengths.
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81.05.Ea III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.61.Ey III-V semiconductors

Electromigration in Cu(Al) and Cu(Mn) damascene lines

C.-K. Hu, J. Ohm, L. M. Gignac, C. M. Breslin, S. Mittal, G. Bonilla, D. Edelstein, R. Rosenberg, S. Choi, J. J. An, A. H. Simon, M. S. Angyal, L. Clevenger, J. Maniscalco, T. Nogami, et al.

J. Appl. Phys. 111, 093722 (2012); http://dx.doi.org/10.1063/1.4711070 (6 pages)

Online Publication Date: 10 May 2012

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The effects of impurities, Mn or Al, on interface and grain boundary electromigration (EM) in Cu damascene lines were investigated. The addition of Mn or Al solute caused a reduction in diffusivity at the Cu/dielectric cap interface and the EM activation energies for both Cu-alloys were found to increase by about 0.2 eV as compared to pure Cu. Mn mitigated and Al enhanced Cu grain boundary diffusion; however, no significant mitigation in Cu grain boundary diffusion was observed in low Mn concentration samples. The activation energies for Cu grain boundary diffusion were found to be 0.74 ± 0.05 eV and 0.77 ± 0.05 eV for 1.5 μm wide polycrystalline lines with pure Cu and Cu (0.5 at. % Mn) seeds, respectively. The effective charge number in Cu grain boundaries Z*GB was estimated from drift velocity and was found to be about −0.4. A significant enhancement in EM lifetimes for Cu(Al) or low Mn concentration bamboo-polycrystalline and near-bamboo grain structures was observed but not for polycrystalline-only alloy lines. These results indicated that the existence of bamboo grains in bamboo-polycrystalline lines played a critical role in slowing down the EM-induced void growth rate. The bamboo grains act as Cu diffusion blocking boundaries for grain boundary mass flow, thus generating a mechanical stress-induced back flow counterbalancing the EM force, which is the equality known as the “Blech short length effect.”
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66.30.Qa Electromigration
61.72.Mm Grain and twin boundaries

Strong asymmetrical doping properties of spinel CoAl2O4

Chunbao Feng, Wan-Jian Yin, Jinlan Nie, Xiaotao Zu, Muhammad N. Huda, Su-Huai Wei, Mowafak M. Al-Jassim, John A. Turner, and Yanfa Yan

J. Appl. Phys. 111, 093723 (2012); http://dx.doi.org/10.1063/1.4716025 (7 pages)

Online Publication Date: 11 May 2012

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Using first-principles density-functional theory, we have investigated the intrinsic and extrinsic doping properties of CoAl2O4 by calculating the transition energies and formation energies of intrinsic and extrinsic defects. We find that CoAl2O4 exhibits strong asymmetrical doping properties: Although excellent p-type conductivity can be achieved by Li or Na doping at O-rich growth condition, n-type conductivity cannot be achieved by any intrinsic or extrinsic dopants at any growth conditions. These asymmetrical doping properties are attributed to the formation of intrinsic defects, particularly AlCo, which has very low formation energy at all growth conditions. Our results suggest that for better use of CoAl2O4, the electronic devices should require CoAl2O4 to exhibit p-type conductivity.
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71.55.Ht Other nonmetals
72.80.Sk Insulators
61.72.jj Interstitials
61.72.up Other materials
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.20.Ps Other inorganic compounds

Rashba spin-orbit effect on tunneling time in graphene superlattice

Edris Faizabadi and Farhad Sattari

J. Appl. Phys. 111, 093724 (2012); http://dx.doi.org/10.1063/1.4714335 (5 pages) | Cited 1 time

Online Publication Date: 14 May 2012

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Based on transfer-matrix and stationary phase methods, we have investigated the tunneling time (group delay time) through monolayer graphene superlattice in the presence of Rashba spin-orbit interaction. It is found that the tunneling time has an oscillatory behavior with respect to Rashba spin-orbit interaction strength. Furthermore, the tunneling time for normal incident angle is independent of spin state of electron, while for oblique incident angles, it depends on the spin state of electron. It is also shown that, for normal incident, the Hartman effect vanishes, while for oblique incident, the Hartman effect appears whenever the x (the growth direction of superlattice) component of the electron wave vector inside the barriers is imaginary.
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73.40.Gk Tunneling
02.60.Dc Numerical linear algebra
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Thermal conductivity of Ce1−xLaxCu4Al Kondo alloys

M. Falkowski and A. Kowalczyk

J. Appl. Phys. 111, 093725 (2012); http://dx.doi.org/10.1063/1.4714548 (5 pages) | Cited 1 time

Online Publication Date: 14 May 2012

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Experimental results of thermal conductivity (κ) for Ce1−xLaxCu4Al alloy series are reported. The hexagonal CeCu5-type structure was confirmed by the powder X-ray diffraction technique. The measured thermal conductivity increases with increasing temperature. The reduced Lorentz number L/L0 of Ce1−xLaxCu4Al increases with cooling and reaches a maximum value at low temperatures. The magnetic contribution to the thermal resistivity Wmag was separated, and it was shown that the product WmagT has a logT-behavior, suggesting of Kondo effect. The log T-behavior for the WmagT is quite similar to that observed as for magnetic resistivity ρmag.
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66.70.Df Metals, alloys, and semiconductors
72.15.Qm Scattering mechanisms and Kondo effect
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