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1 Apr 2009

Volume 105, Issue 7, Articles (07xxxx)

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Modeling semiconductor nanostructures thermal properties: The dispersion role

Damian Terris, Karl Joulain, Denis Lemonnier, and David Lacroix

J. Appl. Phys. 105, 073516 (2009); http://dx.doi.org/10.1063/1.3086409 (9 pages) | Cited 4 times

Online Publication Date: 7 April 2009

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We study heat transport in semiconductor nanostructures by solving the Boltzmann transport equation by means of the discrete ordinate method. Relaxation time and phase and group velocity spectral dependencies are taken into account. The Holland model of phonon relaxation time is revisited and recalculated from dispersion relations (taken in literature) in order to match bulk silicon and germanium values. This improved model is then used to predict silicon nanowire and nanofilm thermal properties in both ballistic and mesoscopic regimes.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
63.22.Gh Nanotubes and nanowires

Photoluminescence properties of SiOx thin films prepared by reactive electron beam evaporation from SiO and silica nanoparticles

Devendraprakash Gautam, Emi Koyanagi, and Takashi Uchino

J. Appl. Phys. 105, 073517 (2009); http://dx.doi.org/10.1063/1.3104772 (8 pages) | Cited 8 times

Online Publication Date: 7 April 2009

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A simple reactive evaporation technique is proposed to obtain highly efficient light emitting Si nanostructures. It is shown that structurally homogeneous SiOx thin films are synthesized by a reactive electron beam evaporation from a mixture of SiO and silica nanoparticles. These SiOx thin films result in the formation of Si nanocrystals on annealing under Ar atmosphere, exhibiting efficient photoluminescence (PL) emission. The composition of SiOx thin films is varied by changing the molar concentration of silica in the mixture. X-ray photoelectron spectroscopy and Fourier transform infrared measurements demonstrate that a chemical reaction between SiO and silica nanoparticles occurs during electron beam irradiation, creating evaporated species in the form of SiOy, (1<y<2). The pivotal role of the homogeneous microscopic structure of as-deposited thin films on the resulting PL yield after annealing is proposed.
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78.66.Nk Insulators
78.55.Hx Other solid inorganic materials
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.aj Insulators
68.55.Nq Composition and phase identification
78.30.Hv Other nonmetallic inorganics
79.60.Dp Adsorbed layers and thin films
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Efficient multiphase green phosphor based on strontium thiogallate

Mihail Nazarov, Do Young Noh, Clare Chisu Byeon, and Hyojung Kim

J. Appl. Phys. 105, 073518 (2009); http://dx.doi.org/10.1063/1.3093932 (8 pages) | Cited 2 times

Online Publication Date: 8 April 2009

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Efficient multiphase green phosphors based on strontium thiogallate were synthesized by solid state reaction at 900–1000 °C with carbon as a reduction atmosphere. The detailed x-ray diffraction analysis, energy dispersive spectroscopy, Raman spectroscopy, and photoluminescence were carried out in order to enlarge the understanding of the radiative processes in multiphase green phosphors based on strontium thiogallate. The crystal field splitting, Stokes shift, redshift, and centroidal shift were estimated, and the results are in good agreement with mathematical calculations. Our study confirms that the proposed multiphase green phosphor based on strontium thiogallate is a good candidate for solid state lighting and display devices with higher intensity and better chromaticity coordinates in comparison with the known commercial phosphors.
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81.05.Cy Elemental semiconductors
78.55.Hx Other solid inorganic materials
78.30.Hv Other nonmetallic inorganics
71.70.Ch Crystal and ligand fields
85.60.Pg Display systems

Magnetic anomaly in Ni51.5Fe21.5Ga27 single crystalline ferromagnetic shape memory alloy studied by ac impedance measurements

M. L. Corró, S. Kustov, E. Cesari, and Y. I. Chumlyakov

J. Appl. Phys. 105, 073519 (2009); http://dx.doi.org/10.1063/1.3106043 (5 pages) | Cited 2 times

Online Publication Date: 8 April 2009

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A magnetic anomaly in the austenitic state of Ni51.5Fe21.5Ga27 single crystalline ferromagnetic shape memory alloy has been studied by means of ac impedance measurements. A much stronger effect of the degree of atomic order on the temperature of this anomaly (as compared to the temperature of the martensitic and para-ferromagnetic transitions) has been found. It has been shown that apart from the previously reported slight variation in the saturation magnetization, the magnetic anomaly results in a nearly one order of magnitude change in the value of initial magnetic permeability. The anomaly is not revealed in the resistive impedance at low frequencies, pointing likely to its purely magnetic origin.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
64.70.kd Metals and alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
81.30.Kf Martensitic transformations

Optical properties of β-Sn films

Katsuki Takeuchi and Sadao Adachi

J. Appl. Phys. 105, 073520 (2009); http://dx.doi.org/10.1063/1.3106528 (6 pages) | Cited 1 time

Online Publication Date: 10 April 2009

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Optical properties of white tin (β-Sn) have been investigated using spectroscopic ellipsometry in the photon-energy range between 0.6 and 6.5 eV at room temperature. The β-Sn films are deposited by vacuum evaporation on Si(001) substrates. The structural properties of the films are evaluated by x-ray diffraction and ex situ atomic force microscopy. The measured ε(E) spectra reveal distinct structures at several interband critical points in the Brillouin zone of β-Sn. These spectra are analyzed on the basis of a simplified model of the interband transitions, including the free-carrier absorption between the filled and empty electronic states. Dielectric-related optical constants, such as the complex refractive index, absorption coefficient, and normal-incidence reflectivity, of bulk β-Sn films are also presented.
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78.66.Bz Metals and metallic alloys
71.20.Be Transition metals and alloys
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.05.cp X-ray diffraction
68.37.Ps Atomic force microscopy (AFM)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.55.-a Thin film structure and morphology
81.05.Bx Metals, semimetals, and alloys

Pulsed laser deposited tetrahedral amorphous carbon with high sp3 fractions and low optical bandgaps

Y. Miyajima, S. J. Henley, G. Adamopoulos, V. Stolojan, E. Garcia-Caurel, B. Drévillon, J. M. Shannon, and S. R. P. Silva

J. Appl. Phys. 105, 073521 (2009); http://dx.doi.org/10.1063/1.3095667 (8 pages) | Cited 7 times

Online Publication Date: 15 April 2009

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Amorphous carbon films with sp3 bonded carbon fractions over 70% are deposited by pulsed laser deposition. However, the optical bandgap obtained from optical transmittance and spectroscopic ellipsometry analysis shows the values to be below 1.0 eV. A wide range of measurements such as electron energy loss spectroscopy, visible Raman, spectroscopic ellipsometry, optical transmittance, and electrical characterization are performed to elucidate the bonding configurations that dictate microstructural, optical and electrical properties, and their linkage to band structure changes. It is found that stress-induced electronic localized states play an important role in the physical properties of the films deposited. The optical bandgap is shown not to be a good measure of the electrical bandgap, especially for high electric field conduction in these tetrahedral amorphous carbon films.
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78.66.Nk Insulators
73.61.Ng Insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.55.aj Insulators
68.55.-a Thin film structure and morphology
81.15.Fg Pulsed laser ablation deposition
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Long-range order on the atomic scale induced at CoFeB/MgO interfaces

Gerrit Eilers, Henning Ulrichs, Markus Münzenberg, Andy Thomas, Karsten Thiel, and Michael Seibt

J. Appl. Phys. 105, 073701 (2009); http://dx.doi.org/10.1063/1.3100044 (4 pages) | Cited 2 times

Online Publication Date: 1 April 2009

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The amorphous (a-) CoFeB/crystalline (c-) MgO based tunneling system interface has been studied by means of quantitative high resolution transmission electron microscopy from atomic to micrometer length scales with increasing annealing temperatures. On the micron scale an irregular nucleation is found. On the atomic scale a long-range order is induced by the MgO interface, explaining the high tunnel magnetoresistance values >100% even for not fully crystallized CoFeB/MgO/CoFeB tunnel junctions.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.-m Magnetotransport phenomena; materials for magnetotransport
68.65.Ac Multilayers
81.40.Gh Other heat and thermomechanical treatments

Synthesis and thermoelectric properties of type-VIII germanium clathrates Sr8AlxGayGe46−x−y

Yuta Sasaki, Kengo Kishimoto, Tsuyoshi Koyanagi, Hironori Asada, and Koji Akai

J. Appl. Phys. 105, 073702 (2009); http://dx.doi.org/10.1063/1.3100205 (8 pages) | Cited 7 times

Online Publication Date: 1 April 2009

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Nominal Sr8AlxGa16−xGe30 samples with x = 6, 8, and 10 crystallized in the type-VIII clathrate structure (Imath3m, No. 217), while the sample with x = 4 crystallized in the type-I clathrate structure (Pmmathn, No. 223). While a large number of the type-I thermoelectric clathrates exist, only three type-VIII clathrates of Ba8Ga16Sn30, Eu8Ga16Ge30, and Sr8AlxGa16−xSi30 had been synthesized before. The type-VIII Sr8AlxGayGe46−x−y samples (6 ≤ x ≤ 7 and 10 ≤ y ≤ 11) with various carrier concentrations were prepared to investigate their thermoelectric properties. They exhibited the temperature dependences of electrical conductivities and the Seebeck coefficients typical of n type degenerate semiconductors, which almost depended on their carrier concentrations systematically. A relatively large dimensionless figure-of-merit ZT of 0.56 at 800 K was obtained for the type-VIII Sr8Al6.3Ga10.3Ge29.4 sample with a carrier concentration of 3.0×1020 cm−3. This ZT value is comparable to that of 0.62 at 800 K for the type-I Sr8Ga16.5Ge29.5 clathrate. The type-VIII clathrate had a smaller effective mass, a higher mobility, and a higher lattice thermal conductivity than those of the type-I clathrate. The difference in transport properties between the type-I and type-VIII clathrates is also discussed.
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72.20.Pa Thermoelectric and thermomagnetic effects
81.20.-n Methods of materials synthesis and materials processing
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
72.20.Ee Mobility edges; hopping transport
72.80.Jc Other crystalline inorganic semiconductors
66.70.Df Metals, alloys, and semiconductors

Quantum confinement effect on the effective mass in two-dimensional electron gas of AlGaN/GaN heterostructures

A. M. Kurakin, S. A. Vitusevich, S. V. Danylyuk, H. Hardtdegen, N. Klein, Z. Bougrioua, A. V. Naumov, and A. E. Belyaev

J. Appl. Phys. 105, 073703 (2009); http://dx.doi.org/10.1063/1.3100206 (6 pages) | Cited 4 times

Online Publication Date: 1 April 2009

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We report the results of direct measurements and a theoretical investigation of the in-plane effective mass in the two-dimensional electron gas of nominally undoped AlGaN/GaN heterostructures with a different degree of quantum confinement. It is shown that in most cases the conduction band nonparabolicity effect is overestimated and the electron wave-function penetration into the barrier layer should be taken into account. The contribution of the wave-function hybridization is determined to play the dominant role. The band edge effective mass value is deduced to be (0.2±0.01)m0.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Resistance switching properties of planner Ag/Li:NiO/Ag structures induced by swift heavy ion irradiation

U. S. Joshi, S. J. Trivedi, K. H. Bhavsar, U. N. Trivedi, S. A. Khan, and D. K. Avasthi

J. Appl. Phys. 105, 073704 (2009); http://dx.doi.org/10.1063/1.3093683 (4 pages) | Cited 3 times

Online Publication Date: 1 April 2009

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We report on the resistance switching induced by swift heavy ion (SHI) irradiation in lithium doped nanostructured NiO thin films grown on MgO (100) substrates by chemical solution deposition. Hysteresis in current-voltage curves were observed for the Ag/Li:NiO/Ag planner structures irradiated with 100 MeV Ag+14 ions, whereas pristine samples showed only linear I-V characteristics. No preferential oxygen loss from the film surface has been detected in on-line elastic recoil detection analysis. This suggests that change in the defect density created by SHI irradiation that may contribute to the metallic filaments play a major role as compared to the interfacial oxygen vacancies in resistance switching of NiO.
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73.40.Rw Metal-insulator-metal structures
61.72.jd Vacancies
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
61.82.Rx Nanocrystalline materials
73.63.Bd Nanocrystalline materials
61.80.Jh Ion radiation effects

Electrical activity of deep traps in high resistivity CdTe: Spectroscopic characterization

B. Fraboni, D. Cavalcoli, A. Cavallini, and P. Fochuk

J. Appl. Phys. 105, 073705 (2009); http://dx.doi.org/10.1063/1.3093697 (6 pages) | Cited 7 times

Online Publication Date: 2 April 2009

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The electrical compensation processes of high resistivity CdTe is controlled by deep levels. We have characterized the electrical activity of deep traps by means of three different and complementary spectroscopic methods: photoinduced current transient spectroscopy, surface photovoltage spectroscopy, and space charge limited current analyses. The aim is twofold: to achieve a thorough characterization of the deep trap properties and to assess the potentiality and limitations of the three experimental techniques by a cross correlation of the results obtained with each one of them. We have obtained a direct quantitative estimate of the major deep trap concentration, and we have assessed the sensitivity limit in deep-level detection for surface photovoltage spectroscopy.
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72.80.Ey III-V and II-VI semiconductors
78.66.Hf II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
72.20.Ht High-field and nonlinear effects
71.55.Gs II-VI semiconductors
72.40.+w Photoconduction and photovoltaic effects

Electronic structure of amorphous silicon oxynitride with different compositions

A. N. Sorokin, A. A. Karpushin, V. A. Gritsenko, and H. Wong

J. Appl. Phys. 105, 073706 (2009); http://dx.doi.org/10.1063/1.3103311 (4 pages) | Cited 2 times

Online Publication Date: 2 April 2009

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A revised tight-binding Hamiltonian parametrization scheme for calculating the electronic structure of both covalent and ion-covalent solids is proposed. Unlike the conventional approaches, the present nonempirical calculation does not rely on any empirical parameter. We use the atomic properties of isolated atoms to construct the matrix elements. Results show that the predicted charge transfer in SiO2 and Si3N4, the bandgap energies of SiO2, Si3N4, and SiOxNy films, as well as the electron and hole barriers at the Si/SiO2, Si/Si3N4, and Si/SiOxNy interfaces are in good agreement with the experimental findings reported in literatures.
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71.23.An Theories and models; localized states
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
71.70.-d Level splitting and interactions
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

Electronic properties of titanium and chromium impurity centers in germanium

J. Lauwaert, J. Van Gheluwe, J. Vanhellemont, E. Simoen, and P. Clauws

J. Appl. Phys. 105, 073707 (2009); http://dx.doi.org/10.1063/1.3082124 (6 pages) | Cited 4 times

Online Publication Date: 2 April 2009

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The electronic properties of the 3d transition metal impurities titanium and chromium in crystalline germanium have been investigated by means of deep level transient spectroscopy. The metals were implanted at 90 keV and diffused deeper into the bulk during a thermal anneal at 500 °C, which yielded spectra specific for the implanted metal. It was found that Ti introduces a deep electron trap and a semishallow hole trap. For Cr one deep electron trap and three hole traps were observed. The capture cross section of the electron traps is thermally activated while three of the hole traps display electric field enhanced emission, which is in agreement with multiple-acceptor states of metal impurities on substitutional sites. It is concluded that Ti in germanium is a double acceptor, while Cr is a triple acceptor with, in addition, a donor level close to the valence band.
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71.55.Cn Elemental semiconductors
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
71.20.Mq Elemental semiconductors

Low temperature electrical transport properties of carbon matrix containing iron nanoparticles

E. P. Sajitha, V. Prasad, and S. V. Subramanyam

J. Appl. Phys. 105, 073708 (2009); http://dx.doi.org/10.1063/1.3095762 (6 pages) | Cited 3 times

Online Publication Date: 6 April 2009

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We present a comparative study of the low temperature electrical transport properties of the carbon matrix containing iron nanoparticles and the films. The conductivity of the nanoparticles located just below the metal-insulator transition exhibits metallic behavior with a logarithmic temperature dependence over a large temperature interval. The zero-field conductivity and the negative magnetoresistance, showing a characteristic upturn at liquid helium temperature, are consistently explained by incorporating the Kondo relation and the two dimensional electron-electron interaction. The films, in contrast, exhibit a crossover of the conductivity from power-law dependence at high temperatures to an activated hopping law dependence in the low temperature region. The transition is attributed to changes in the energy dependence of the density of states near the Fermi level. The observed magnetoresistance is discussed in terms of quantum interference effect on a three-dimensional variable range hopping mechanism.
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72.20.Ee Mobility edges; hopping transport
71.30.+h Metal-insulator transitions and other electronic transitions
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
75.50.Tt Fine-particle systems; nanocrystalline materials
71.20.Ps Other inorganic compounds
72.20.My Galvanomagnetic and other magnetotransport effects
73.61.Ng Insulators

Thermal transport properties of polycrystalline tin-doped indium oxide films

Toru Ashida, Amica Miyamura, Nobuto Oka, Yasushi Sato, Takashi Yagi, Naoyuki Taketoshi, Tetsuya Baba, and Yuzo Shigesato

J. Appl. Phys. 105, 073709 (2009); http://dx.doi.org/10.1063/1.3093684 (4 pages) | Cited 11 times

Online Publication Date: 13 April 2009

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Thermal diffusivity of polycrystalline tin-doped indium oxide (ITO) films with a thickness of 200 nm has been characterized quantitatively by subnanosecond laser pulse irradiation and thermoreflectance measurement. ITO films sandwiched by molybdenum (Mo) films were prepared on a fused silica substrate by dc magnetron sputtering using an oxide ceramic ITO target (90 wt % In2O3 and 10 wt % SnO2). The resistivity and carrier density of the ITO films ranged from 2.9×10−4 to 3.2×10−3 Ω cm and from 1.9×1020 to 1.2×1021 cm−3, respectively. The thermal diffusivity of the ITO films was (1.5–2.2)×10−6 m2/s, depending on the electrical conductivity. The thermal conductivity carried by free electrons was estimated using the Wiedemann–Franz law. The phonon contribution to the heat transfer in ITO films with various resistivities was found to be almost constant (λph = 3.95 W/m K), which was about twice that for amorphous indium zinc oxide films.
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66.30.Xj Thermal diffusivity
68.55.ag Semiconductors
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
81.15.Cd Deposition by sputtering
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.66.Li Other semiconductors

Thermoelectric power factors of nanocarbon ensembles as a function of temperature

D. M. Gruen, P. Bruno, R. Arenal, J. Routbort, D. Singh, and M. Xie

J. Appl. Phys. 105, 073710 (2009); http://dx.doi.org/10.1063/1.3103244 (10 pages) | Cited 2 times

Online Publication Date: 13 April 2009

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Thermoelectric power factors of nanocarbon ensembles have been determined as a function of temperature from 400 to 1200 K. The ensembles, composed of mixtures of nanographite or disperse ultrananocrystalline diamond with B4C, are formed into mechanically rigid compacts by reaction at 1200 K with methane gas and subsequently annealed in an argon atmosphere at temperatures up to 2500 K. The ensembles were characterized using scanning electron microscopy, Raman, x-ray diffraction, and high resolution transmission electron microscopy techniques and found to undergo profound nanostructural changes as a function of temperature while largely preserving their nanometer sizes. The power factors increase strongly both as a function of annealing temperature and of the temperature at which the measurements are carried out reaching 1 μW/K2 cm at 1200 K without showing evidence of a plateau. Density functional “molecular analog” calculations on systems based on stacked graphene sheets show that boron substitutional doping results in a lowering of the Fermi level and the creation of a large number of hole states within thermal energies of the Fermi level [ P. C. Redfern, D. M. Greun, and L. A. Curtiss, Chem. Phys. Lett. 471, 264 (2009) ]. We propose that enhancement of electronic configurational entropy due to the large number of boron configurations in the graphite lattice contributes to the observed thermoelectric properties of the ensembles.
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72.20.Pa Thermoelectric and thermomagnetic effects
73.63.-b Electronic transport in nanoscale materials and structures
78.30.Hv Other nonmetallic inorganics
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
73.22.-f Electronic structure of nanoscale materials and related systems
81.05.U- Carbon/carbon-based materials
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Electrical transport measurements of highly conductive carbon nanotube/poly(bisphenol A carbonate) composite

Seamus A. Curran, Jamal Talla, Sampath Dias, Donghui Zhang, David Carroll, and Donald Birx

J. Appl. Phys. 105, 073711 (2009); http://dx.doi.org/10.1063/1.3073938 (5 pages) | Cited 12 times

Online Publication Date: 13 April 2009

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Acid-treated and pristine chemical vapor deposition grown multiwalled carbon nanotube (MWNT) and poly(bisphenol A carbonate) (PC) composites were prepared through a simple solution blending with varied nanotube weight fractions. The electrical conductivities of the composites can be described by the scaling law based on percolation theory with unprecedented high saturated ac conductivity of pristine nanotubes (σsat = 1598.4 S cm−1, pc = 0.19 wt %) and acid-treated nanotubes (σsat = 435.4 S cm−1, pc = 0.3 wt %), which correlates well with the dc behavior. We attribute the high saturated conductivities to managing the dispersions, rather than looking to have a well dispersed three-dimensional network thin film. The comparison was made between acid-treated nanotubes and pristine nanotube, both dispersed in PC at various loadings. It was found that the pristine nanotubes in PC possessed an even higher conductivity than the more evenly dispersed composites consisting of lightly acid-treated MWNT in PC.
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73.63.Fg Nanotubes
72.80.Tm Composite materials
81.05.Qk Reinforced polymers and polymer-based composites
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Investigation of iron impurity gettering at dislocations in a SiGe/Si heterostructure

Jinggang Lu, Xuegong Yu, Yongkook Park, and George Rozgonyi

J. Appl. Phys. 105, 073712 (2009); http://dx.doi.org/10.1063/1.3093912 (6 pages)

Online Publication Date: 14 April 2009

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This article examined the electrical activities of dislocations in a SiGe/Si heterostructure by deep level transient spectroscopy (DLTS) after iron contamination and phosphorous diffusion gettering. DLTS of iron contaminated samples revealed a peak at 210 K, which was assigned to individual iron atoms or very small (<2 nm) precipitates decorated along dislocations, considering that the iron contamination annealing was terminated by quenching and transmission electron microscopy did not reveal any precipitate at dislocations. Arrhenius plot of the 210 K peak yielded a hole capture cross section of 2.4×10−14 cm2 and an energy level of 0.42 eV above the valance band. The relatively large hole capture cross section indicates strong interactions between iron-related deep levels and the dislocation shallow bands. DLTS of the iron contaminated sample revealed that 6×1014 cm−3 of boron can more effectively trap interstitial iron at room temperatures than the strain field/defect sites at 107–108 cm−2 dislocations. Phosphorous diffusion experiments revealed that the gettering efficiency of iron impurities depends on the dislocation density. For regions of high dislocation density, phosphorous diffusion cannot remove all iron impurities decorated at dislocations, suggesting a strong binding of iron impurities at dislocation core defects.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
71.55.Cn Elemental semiconductors
66.30.Lw Diffusion of other defects
72.80.Cw Elemental semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.72.Cc Kinetics of defect formation and annealing
61.72.Yx Interaction between different crystal defects; gettering effect

Enhanced thermoelectric performance of AgSbTe2 synthesized by high pressure and high temperature

Taichao Su, Xiaopeng Jia, Hongan Ma, Fengrong Yu, Yongjun Tian, Guihong Zuo, Youjin Zheng, Yiping Jiang, Dan Dong, Le Deng, Bingke Qin, and Shizhao Zheng

J. Appl. Phys. 105, 073713 (2009); http://dx.doi.org/10.1063/1.3106102 (4 pages) | Cited 10 times

Online Publication Date: 15 April 2009

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Near single phase ternary bulk thermoelectric material AgSbTe2 was synthesized by high pressure and high temperature (HPHT) method. The temperature-dependent thermoelectric properties including Seebeck coefficient, electrical conductivity, and thermal conductivity were studied. The HPHT synthesized AgSbTe2 sample has higher thermoelectric performance in the measured temperature range than that of the same sample prepared at normal pressure. The enhanced thermoelectric properties should be attributed to the HPHT quenching which keeps partially the high electrical conductivity of AgSbTe2 under high pressure.
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72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Jc Other crystalline inorganic semiconductors
81.05.Hd Other semiconductors
62.50.-p High-pressure effects in solids and liquids
81.40.Gh Other heat and thermomechanical treatments
66.70.Df Metals, alloys, and semiconductors
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Antiferromagnetic-spin-fluctuation-mediated pairing as a likely mechanism for unconventional superconductivity in LaAg1−cMnc alloys

S. Kumar, S. N. Kaul, J. Rodríguez Fernández, and L. Fernández Barquín

J. Appl. Phys. 105, 073901 (2009); http://dx.doi.org/10.1063/1.3099600 (14 pages) | Cited 2 times

Online Publication Date: 1 April 2009

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Electrical resistivity, ac magnetic susceptibility, specific heat, dc magnetization, and dc magnetic susceptibility of superconducting LaAg1−cMnc alloys with c = 0.0, 0.025, 0.05. 0.1, 0.2, and 0.3 have been measured in the temperature range of 0.35 K ≤ T ≤ 300 K at external magnetic fields ranging from 0 to 90 kOe with a view to unravel the exact nature of the superconducting ground state. In these alloys, each Mn atom carries a magnetic moment of ≅ 4μB. A comparison of the results of these investigations with the predictions of the existing theoretical models permits us to make a number of interesting observations that include the following. The intermetallic compound LaAg is an archetypal Bardeen–Cooper–Schrieffer (BCS) spin-singlet isotropic even-parity s-wave superconductor with a superconducting transition temperature of Tc = 0.97 K. At low solute concentrations of c ≈ 0.03, Mn substitutes for La at the La sublattice sites in the LaAg parent compound and Tc suddenly drop from 0.97 to temperatures below 0.35 K, reflecting thereby the destruction of conventional phonon-mediated s-wave superconductivity of the LaAg host by pair-breaking magnetic (Mn) impurities. At a threshold concentration of Mn, c ≅ 0.05 (which corresponds to the antiferromagnetic instability/critical phase boundary in the magnetic phase diagram), superconducting gap opens up, Tc abruptly shoots up to 5 K, and unconventional superconductivity sets in at ambient pressure for T ≤ Tc. Beyond this threshold concentration, Mn has exclusive site preference for Ag at the Ag sublattice sites in LaAg and Tc increases from 5 to 6 K. The unconventional nature of superconductivity at these solute concentrations is signaled by strong departures from the BCS predictions. We present ample experimental evidence that favors antiferromagnetic-spin-fluctuation-mediated pairing as the most likely mechanism for the unconventional (d-wave) superconductivity observed in LaAg1−cMnc alloys with c ≥ 0.05.
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74.25.Ha Magnetic properties including vortex structures and related phenomena
74.20.Rp Pairing symmetries (other than s-wave)
74.20.Mn Nonconventional mechanisms
74.25.F- Transport properties
75.30.Ds Spin waves
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)

Fundamental and harmonic submillimeter-wave emission from parallel Josephson junction arrays

Faouzi Boussaha, Morvan Salez, Alexandre Féret, Benoit Lecomte, Christine Chaumont, Michel Chaubet, Frédéric Dauplay, Yan Delorme, and Jean-Michel Krieg

J. Appl. Phys. 105, 073902 (2009); http://dx.doi.org/10.1063/1.3099602 (7 pages) | Cited 2 times

Online Publication Date: 1 April 2009

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We report heterodyne measurements of Josephson microwave radiation emitted by a parallel array of small superconductor-insulator-superconductor (SIS) junctions at submillimeter-wave frequencies. The array consists of five Nb/Al–AlOx/Nb junctions nonevenly distributed in a niobium superconducting stripline, and is optimized for rf coupling in the 450–640 GHz range. We observed Fiske-like resonant steps in its I-V curve in the presence of magnetic field. The device was placed in a waveguide mount, and its radiation was quasioptically coupled out of the cryostat, to a SIS-mixer spectrometer in the same frequency range, with a 4–8 GHz band for spectral analysis. We detected a coherent signal in the spectra when the array was biased on the first and third steps, respectively, at the first harmonic frequency of 242 GHz and at the fundamental frequency of 493 GHz, both being the Josephson frequencies associated with their dc voltages. This strongly suggests that this type of parallel arrays optimized for wideband rf coupling, though strongly discretized, hosts dynamic fluxon regimes similar to long Josephson junctions, which could find applications in superconducting digital electronics or integrated heterodyne submillimeter-wave receivers.
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85.25.Cp Josephson devices
84.40.Az Waveguides, transmission lines, striplines

Epitaxial film growth and optoelectrical properties of layered semiconductors, LaMnXO (X = P, As, and Sb)

Kentaro Kayanuma, Hidenori Hiramatsu, Toshio Kamiya, Masahiro Hirano, and Hideo Hosono

J. Appl. Phys. 105, 073903 (2009); http://dx.doi.org/10.1063/1.3093685 (7 pages) | Cited 8 times

Online Publication Date: 2 April 2009

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Thin films of LaMnXO (X = P, As, and Sb), which are isostructural compounds of the newly discovered superconductor, LaFeAsO, were grown epitaxially on MgO (001) substrates at ∼ 680 °C by pulsed laser deposition. Postdeposition thermal annealing at 1000 °C in evacuated silica glass ampoules improved the crystallinity and orientation for the LaMnPO and LaMnAsO films, but it led to the phase segregation of the LaMnSbO film. Thermopower and optical absorption measurements revealed that all the films are p-type semiconductors with indirect bandgaps from 1.0 to 1.4 eV, which are supported by density functional calculations with the GGA+U approximation.
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68.55.ag Semiconductors
78.66.Li Other semiconductors
72.40.+w Photoconduction and photovoltaic effects
73.50.Lw Thermoelectric effects
81.15.Fg Pulsed laser ablation deposition
81.16.Mk Laser-assisted deposition

Patterned media with composite structure for writability at high areal recording density

Rachid Sbiaa, Kyaw Oo Aung, S. N. Piramanayagam, Ei-Leen Tan, and Randall Law

J. Appl. Phys. 105, 073904 (2009); http://dx.doi.org/10.1063/1.3093699 (4 pages) | Cited 18 times

Online Publication Date: 2 April 2009

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Writability in bit-patterned media (BPM) is a critical issue for high areal densities. In this study, magnetization reversal for multilayer of (Co/Pd) nanodots was investigated using magnetic force microscopy. We observed an increase of more than 15 times in switching field (Hsw) in BPM over that of continuous films. An exchange coupled structure made of a thin Co layer with in-plane magnetization and high perpendicular anisotropy layer of (Co/Pd) multilayer to reduce the switching field is proposed. When the Co layer is thinner than 2 nm, its magnetization is aligned perpendicular to the film plane due to the exchange coupling with the 15 nm thick (Co/Pd) multilayer. The thin Co layer helps in reducing the Hsw of (Co/Pd) by almost 50% and also its distribution by 57% as measured from remanence magnetization.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Jk Magnetization reversal mechanisms
75.30.Gw Magnetic anisotropy
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ss Magnetic recording materials

Coexistence of superparamagnetic and superspin glass behaviors in Co50Ni50 nanoparticles embedded in the amorphous SiO2 host

M. Thakur, M. Patra, S. Majumdar, and S. Giri

J. Appl. Phys. 105, 073905 (2009); http://dx.doi.org/10.1063/1.3103320 (6 pages) | Cited 8 times

Online Publication Date: 2 April 2009

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We investigate the magnetic properties of the nanoparticles of Co50Ni50 alloy embedded in the amorphous SiO2 host with volume fractions, ϕ = 5% and 10%. The static and dynamic aspects of the magnetic properties are investigated by temperature and time dependence of low-field dc magnetization and frequency dependence of ac susceptibilities. The experimental results and analyses suggest that the dilution of the Co50Ni50 nanoparticles belongs to the crossover regime from superparamagnetic to superspin glass states, which are distinguished from the atomic canonical spin glasses.
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75.75.-c Magnetic properties of nanostructures
75.50.Lk Spin glasses and other random magnets
75.50.Tt Fine-particle systems; nanocrystalline materials
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
75.20.En Metals and alloys

Thermopower of Co-doped FeSe

Evan Lyle Thomas, Winnie Wong-Ng, Daniel Phelan, and Jasmine N. Millican

J. Appl. Phys. 105, 073906 (2009); http://dx.doi.org/10.1063/1.3100198 (5 pages) | Cited 5 times

Online Publication Date: 3 April 2009

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The effect of cobalt doping on the thermopower of the superconductor FeSe is investigated through electrical and thermal transport measurements. Our results point to the destruction of superconductivity at very low Co concentrations. Thermopower data suggest negative charge carriers along with a large enhancement of the Seebeck coefficient, S, on the order of ≈ −80 μV/K near T = 100 K.
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74.25.F- Transport properties
61.72.U- Doping and impurity implantation
74.70.-b Superconducting materials other than cuprates
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