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1 Apr 1999

Volume 85, Issue 7, pp. 3395-3936

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Role of the substrate strain in the sheet resistance stability of NiSi deposited on Si(100)

Eliane Maillard-Schaller, B. I. Boyanov, S. English, and R. J. Nemanich

J. Appl. Phys. 85, 3614 (1999); http://dx.doi.org/10.1063/1.369774 (5 pages) | Cited 8 times

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In order to study the influence of strain on the formation and stability of NiSi, Ni has been deposited on strained and relaxed Si(100) n-type substrates. Strained Si substrates have been produced by depositing a pseudomorphic silicon film onto a 3000 Å thick relaxed Si0.8Ge0.2 film. Raman spectroscopy has established that the silicon film is strained. The presence of a characteristic cross-hatch pattern has been identified by atomic force microscopy. Measurements show that the sheet resistance (Rs) of the silicide formed on strained silicon remains stable up to 700 °Cwhile the Rs of the silicide formed on bulk silicon (100) shows a significant increase at 600 °C. X-ray photoelectron spectroscopy shows that the NiSi–NiSi2 phase transition occurs at a higher temperature and is, therefore, not responsible for the Rs instability. Scanning electron microscopy measurements indicate that islanding occurs in the temperature region of the resistivity increase. Photoelectron emission microscopy has been employed to observe the surface morphology during annealing, and islanding is not observed until a higher annealing temperature for the NiSi on strained Si. The increase in Rs is apparently correlated to the islanding of NiSi which appears at lower temperature on the bulk silicon substrate than on the strained silicon substrate. The stability of the NiSi film on the strained Si substrate is related to the strain induced by thermal expansion and the increased lattice constant of the strained Si. © 1999 American Institute of Physics.
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73.61.At Metal and metallic alloys
78.30.Am Elemental semiconductors and insulators
85.40.Ls Metallization, contacts, interconnects; device isolation
68.35.B- Structure of clean surfaces (and surface reconstruction)
79.60.Jv Interfaces; heterostructures; nanostructures
68.35.Fx Diffusion; interface formation
68.35.Gy Mechanical properties; surface strains

Structural and magnetoresistive properties of La0.7Ca0.3Mn0.96(Al1−xInx)0.04O3

J. R. Sun, G. H. Rao, X. R. Gao, J. K. Liang, H. K. Wong, and B. G. Shen

J. Appl. Phys. 85, 3619 (1999); http://dx.doi.org/10.1063/1.369723 (4 pages) | Cited 13 times

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Structural, magnetic, and transport properties of ABO3-type La0.7Ca0.3Mn0.96(Al1−xInx)0.04O3 are investigated. Different structure deformation from that in the A-site doping, characterized by the synchronous variation of the lattice constants b with c/√ versus the content of In in the compounds, is observed. The metal–semiconductor transition shows a strong In content dependence. The transition temperature decreases monotonously from 180.7 to 103.4 K as x varies from 0 to 1, with a corresponding maximum resistivity ranging from 2.9 to 410.8 Ω cm. The magnetoresistive properties of the materials are strongly affected by the size mismatch between A- and B-site ions, and a relation similar to that presented by Hwang et al. [Phys. Rev. Lett. 75, 914 (1995)] is observed though controlling of the tolerance factor, is realized by B-site doping. © 1999 American Institute of Physics.
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75.47.Gk Colossal magnetoresistance
72.60.+g Mixed conductivity and conductivity transitions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Dd Nonmetallic ferromagnetic materials
61.66.Fn Inorganic compounds

Electrical resistivity of silver–silica nanocomposites

S. Banerjee and D. Chakravorty

J. Appl. Phys. 85, 3623 (1999); http://dx.doi.org/10.1063/1.369724 (3 pages) | Cited 4 times

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Nanoparticles of silver with diameters in the range 10.3–25.7 nm were grown within a silica gel medium by an electrodeposition technique. The dc resistivity of the nanocomposites was measured over the temperature range 100–300 K. The resistivity as a function of inverse temperature shows a maximum at around 175 K. This is explained as arising due to the presence of two conduction mechanisms, viz., an electron tunnelling between metal particles and conduction through a percolated metal structure which is fractal in nature. © 1999 American Institute of Physics.
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72.20.Fr Low-field transport and mobility; piezoresistance
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization

Carrier recombination at silicon–silicon nitride interfaces fabricated by plasma-enhanced chemical vapor deposition

Jan Schmidt and Armin G. Aberle

J. Appl. Phys. 85, 3626 (1999); http://dx.doi.org/10.1063/1.369725 (8 pages) | Cited 47 times

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Using the light-biased microwave-detected photoconductance decay method, injection level dependent measurements of the effective surface recombination velocity Seff at silicon surfaces passivated by plasma-enhanced chemical vapor deposited (PECVD) silicon nitride (SiNx) films are performed on monocrystalline silicon wafers of different resistivities and doping types. In order to theoretically simulate the measured dependences of Seff on the bulk injection level Δn, the extended Shockley-Read-Hall formalism is used. Simulation input parameters are the energy dependent interface state densities and capture cross sections of the involved interface defects as well as the positive insulator charge density Qf. The energy dependent properties of the interface defects are experimentally determined by means of small-pulse deep-level transient spectroscopy. These measurements reveal the existence of three “deep” silicon dangling bond defects at the Si-SiNx interface with similar interface state densities but very different capture cross sections and hence recombination rates. Another defect is found very close ( ⩽ 0.1 eV) to the edge of the silicon conduction band. This defect is identified with the K+ center which is responsible for the large positive Qf values ( ∼ 1012 cm−2) at Si-SiNx interfaces obtained from standard dark capacitance-voltage measurements. In order to get a good agreement between measured and calculated Seff(Δn) dependences, a reduction of Qf by one order of magnitude is found to be necessary. The explanation for this reduction is the capture of electrons from the silicon conduction band into the K+ centers. The comparison of Si-SiNx interfaces fabricated by different PECVD techniques shows that the dominant interface defect is produced by the ion bombardment during the SiNx deposition. Thus, avoidance of the ion bombardment leads to a strongly reduced interface recombination and hence a better surface passivation quality. © 1999 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.25.+i Surface conductivity and carrier phenomena
73.20.At Surface states, band structure, electron density of states
72.40.+w Photoconduction and photovoltaic effects
81.65.Rv Passivation
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Effective diffusion lengths for minority carriers in solar cells as determined from internal quantum efficiency analysis

Rolf Brendel and Uwe Rau

J. Appl. Phys. 85, 3634 (1999); http://dx.doi.org/10.1063/1.369726 (4 pages) | Cited 8 times

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We introduce a general relationship between the effective diffusion length LQ of solar cells derived from spectral quantum efficiency Q and the effective diffusion length LJ that determines the saturation current j0 = qn0D/LJ of the diode in the dark. The general relation LQ ≥ LJ holds in the presence of grain boundaries and of spatially nonhomogeneous doping profiles. We find the relation LQ = LJ for solar cells without potential fluctuations at the collecting junction.© 1999 American Institute of Physics.
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84.60.Jt Photoelectric conversion
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Modeling the optical constants of GaP, InP, and InAs

Aleksandra B. Djurišić, Aleksandar D. Rakić, Paul C. K. Kwok, E. Herbert Li, and Martin L. Majewski

J. Appl. Phys. 85, 3638 (1999); http://dx.doi.org/10.1063/1.369727 (5 pages) | Cited 8 times

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An extension of the Adachi model with the adjustable broadening function, instead of the Lorentzian one, is employed to model the optical constants of GaP, InP, and InAs. Adjustable broadening is modeled by replacing the damping constant with the frequency-dependent expression. The improved flexibility of the model enables achieving an excellent agreement with the experimental data. The relative rms errors obtained for the refractive index equal 1.2% for GaP, 1.0% for InP, and 1.6% for InAs. © 1999 American Institute of Physics.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Current responsivity of semiconductor superlattice THz-photon detectors

Anatoly A. Ignatov and Antti-Pekka Jauho

J. Appl. Phys. 85, 3643 (1999); http://dx.doi.org/10.1063/1.369728 (12 pages) | Cited 23 times

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The current responsivity of a semiconductor superlattice THz-photon detector is calculated using an equivalent circuit model which takes into account the finite matching efficiency between a detector antenna and the superlattice in the presence of parasitic losses. Calculations performed for currently available superlattice diodes show that both the magnitudes and the roll-off frequencies of the responsivity are strongly influenced by an excitation of hybrid plasma-Bloch oscillations which are found to be eigenmodes of the system in the THz-frequency band. The expected room temperature values of the responsivity (2–3 A/W in the 1–3 THz-frequency band) range up to several percents of the quantum efficiency e/ℏω of an ideal superconductor tunnel junction detector. Properly designed semiconductor superlattice detectors may thus demonstrate better room temperature THz-photon responsivity than conventional Schottky junction devices. © 1999 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
73.50.Mx High-frequency effects; plasma effects
73.61.-r Electrical properties of specific thin films

Thermoelectric transport properties of n-doped and p-doped Bi0.91Sb0.09 alloy thin films

Sunglae Cho, Antonio DiVenere, George K. Wong, John B. Ketterson, and Jerry R. Meyer

J. Appl. Phys. 85, 3655 (1999); http://dx.doi.org/10.1063/1.369729 (6 pages) | Cited 11 times

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In order to understand the doping behavior of extremely narrow band gap materials and to optimize their characteristics for use in a thermoelectric module, we performed n- and p-type doping experiments on semiconducting Bi0.91Sb0.09 alloy thin films using the group VI(IV) element Te(Sn) as donor (acceptor). Thermoelectric power (TEP), electrical resistivity, and Hall effect were studied in the range of temperatures 5–300 K. Increased Sn doping causes the TEP to change sign (from negative to positive) and the maximum in the TEP can be controlled with the dopant concentration. Increased Te doping causes the TEP to decrease. The maximum Te-doped electron concentration was about 5×1020 cm−3 and the highest Sn-doped hole concentration was about 1×1021 cm−3. Highly Sn- and Te-doped samples show degenerate behavior in the electrical resistivity, TEP and Hall measurements. © 1999 American Institute of Physics.  
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73.50.Lw Thermoelectric effects
73.61.Le Other inorganic semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
61.72.up Other materials

Formation of modified Si/SiO2 interfaces with intrinsic low defect concentrations

L. G. Gosset, J. J. Ganem, H. J. von Bardeleben, S. Rigo, I. Trimaille, J. L. Cantin, T. Åkermark, and I. C. Vickridge

J. Appl. Phys. 85, 3661 (1999); http://dx.doi.org/10.1063/1.369730 (5 pages) | Cited 15 times

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The modification by postoxidation NO treatments of the Si/SiO2 interface in thermally grown Si(100)/SiO2 layers has been studied by nuclear reaction analysis and electron paramagnetic resonance spectroscopy. Our results demonstrate a selective incorporation of NO molecules at the Si/SiO2 interface and a drastic reduction in the interface defect density. In this new configuration, the Pb center density, which is typically 2×1012 cm−2 in the as oxidized samples, is reduced to below 1011 cm−2 without any hydrogen passivation. The thermal treatment in NO atmospheres opens the perspective for the formation of hydrogen free low defect Si(100)/SiOxNy interfaces conserving the qualities of the SiO2 dielectric. © 1999 American Institute of Physics.  
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68.35.Dv Composition, segregation; defects and impurities
81.65.Mq Oxidation
81.65.Rv Passivation
81.05.Cy Elemental semiconductors

Interface characterization of nanocrystalline CdS/Au junction by current–voltage and capacitance–voltage studies

B. K. Patel, K. K. Nanda, and S. N. Sahu

J. Appl. Phys. 85, 3666 (1999); http://dx.doi.org/10.1063/1.369731 (5 pages) | Cited 18 times

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A Schottky junction in the configuration ITO/nano-CdS/Au has been fabricated and the current(I)–voltage(V) and capacitance(C)–voltage(V) characteristics studied. The I–V studies show series resistance effect resulting in two ideality factors: one in low and the other in high forward bias regime, suggesting the presence of surface/interface traps in nano-CdS. Frequency dependent capacitance has also been studied and different semiconductor parameters have been estimated from the I–V and C–V analysis. © 1999 American Institute of Physics.
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68.35.Ct Interface structure and roughness
73.40.Ns Metal-nonmetal contacts

Measurements and modelling of the barrier heights and ideality factors in the metal/conducting polymer composite Schottky device

S. Bandyopadhyay, A. Bhattacharyya, and S. K. Sen

J. Appl. Phys. 85, 3671 (1999); http://dx.doi.org/10.1063/1.369732 (6 pages) | Cited 25 times

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Metal/polymer Schottky contacts have been fabricated using electrochemically prepared free standing thin films of conducting polyaniline/polycarbonate composite as well as conducting polyaniline pellets with various metals such as Al, In, Pb and Sn. The current–voltage characteristics have been studied from room temperature down to 100 K. The data have been analyzed and interpreted on the basis of the thermionic emission mechanism. The barrier height varies from 0.6 to 0.7 V for pellet and from 0.7 to 0.8 V for composite films. There is little dependence of metal on the work function. The ideality factor is dependent on the amount of polyaniline incorporation in polycarbonate, as indicated by the shift in the carbonyl peak in the Fourier transform infrared spectrum. The abnormal decrease in barrier height and increase of ideality factor with decrease in temperature have been interpreted assuming a Gaussian distribution of barrier heights at the interface. This takes account of the nonuniformity and inhomogeneities at the interface. As in the case of inorganic semiconductor diodes, the analysis indicates an apparent decrease in zero bias height and nonlinearity in activation plots. The bias dependence of barrier height and standard deviation causing an increase in ideality factor at low temperature has also been explored. © 1999 American Institute of Physics.
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85.30.Hi Surface barrier, boundary, and point contact devices
85.30.Kk Junction diodes
73.30.+y Surface double layers, Schottky barriers, and work functions
78.66.Qn Polymers; organic compounds
78.30.Jw Organic compounds, polymers

Theoretical study of the energetics, strain fields, and semicoherent interface structures in layer-by-layer semiconductor heteroepitaxy

Luis A. Zepeda-Ruiz, Dimitrios Maroudas, and W. Henry Weinberg

J. Appl. Phys. 85, 3677 (1999); http://dx.doi.org/10.1063/1.369733 (19 pages) | Cited 28 times

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A theoretical analysis based on continuum elasticity theory and atomistic simulations is presented of the interfacial stability with respect to misfit dislocation formation, the strain fields, and the film surface morphology during layer-by-layer semiconductor heteroepitaxy. The strain in the coherently strained films, the energetics of the transition from a coherent to a semicoherent interface consisting of misfit dislocation arrays or networks, the structure of the corresponding semicoherent interfaces, the strain fields associated with different equilibrium states of strain, and the morphological characteristics of the film surfaces are calculated for InAs/GaAs(110) and InAs/GaAs(111)A. The thickness of the epitaxial film is used as the dynamical variable in the analysis. Critical film thicknesses for transition from one equilibrium state of strain to another are computed. The analysis is presented for the more general case of heteroepitaxy on a finite-thickness compliant substrate, while the common case of epitaxy on an infinitely thick substrate is derived as an asymptotic limit of the general case. Continuum elasticity theory is found to describe the atomistic simulation results very well, down to the monolayer-thickness limit. Our theoretical results are discussed in the context of recent experimental data. © 1999 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.35.Ct Interface structure and roughness
62.20.D- Elasticity
68.35.Gy Mechanical properties; surface strains
61.72.Bb Theories and models of crystal defects
61.72.Lk Linear defects: dislocations, disclinations

Electrical properties of K-doped superfulleride thin films

Nathan Swami, Mark E. Thompson, and Bruce E. Koel

J. Appl. Phys. 85, 3696 (1999); http://dx.doi.org/10.1063/1.369734 (5 pages) | Cited 2 times

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K-doped superfulleride films (KxC60, x>6) of an average homogeneous composition of K11±0.3C60 and a strong [111] texture were prepared by depositing C60 on K multilayers at 200 K, in a proportion such that K:C60>12:1, and then annealing these layers to 300 K. This K11C60 superfulleride film was doped with C60 to form another superfulleride phase of average composition K8C60 and then doped further with C60 to form homogeneous K6C60 and K3C60 fulleride phases. The electrical properties of these superfulleride films are compared to those of alkali metal fulleride and alkaline earth metal fulleride films. The doping-resistivity profile showed a resistivity minimum, ρmin1 = 4.0×10−3 Ω cm due to the half filled t1u band in K3C60 and another dip in resistivity to 9.5×10−3 Ω cm at higher K-doping levels of K11C60, presumably due to the unfilled t1g band, as in the alkaline earth metal fullerides. The resistivity of the K3C60 and K11C60 films showed only minimal variations with film thickness, probably because the films prepared in this study had large grain sizes, and hence, resistivity was invariant with film thickness. The temperature dependence of the resistivity for 300 Å films of K3C60, K8C60, and K11C60 was also studied in the 200–350 K temperature range. K11C60 films showed a metallic behavior like K3C60 films, while conduction in K8C60 films exhibited an activated behavior that could be described by a granular metal model for resistivity in the dielectric region. © 1999 American Institute of Physics.
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73.61.Wp Fullerenes and related materials
61.72.Cc Kinetics of defect formation and annealing
68.55.-a Thin film structure and morphology
61.48.-c Structure of fullerenes and related hollow and planar molecular structures

Effects of barrier height fluctuations and electron tunneling on the reverse characteristics of 6H–SiC Schottky contacts

L. Zheng, R. P. Joshi, and Christian Fazi

J. Appl. Phys. 85, 3701 (1999); http://dx.doi.org/10.1063/1.369735 (7 pages) | Cited 12 times

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Analytic calculations of electron transport across a Schottky barrier in 6H–silicon carbide are presented. The treatment includes the effect of barrier height fluctuations and image charge lowering on both the thermionic emission and electron tunneling processes. The results show that barrier height inhomogeneities are very important, and can lead to reverse current densities that are orders of magnitude higher than obtained from a simple theory. Formation of detrimental filamentary currents are predicted. The results are in very good agreement with published experimental data at 300 K. Finally, under forward biasing conditions, the analytical theory yields ideality factors of 1.037 in close agreement with measurements. © 1999 American Institute of Physics.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Gk Tunneling
73.40.Ns Metal-nonmetal contacts
79.40.+z Thermionic emission
73.61.Le Other inorganic semiconductors

Towards stimulated generation of coherent plasmons in nanostructures

K. Kempa, P. Bakshi, C. G. Du, G. Feng, A. Scorupsky, G. Strasser, C. Rauch, K. Unterrainer, and E. Gornik

J. Appl. Phys. 85, 3708 (1999); http://dx.doi.org/10.1063/1.369736 (5 pages) | Cited 3 times

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A possible generation scheme for growing coherent plasma oscillations (plasma instability) is presented. Specific quantum well structures, where a sufficient population inversion can be maintained in the carrier distribution by appropriate injection–extraction configurations, form the basis of this scheme. Self-consistent random phase approximation calculations show that a population inversion, leading to a plasma instability, can occur in such structures. A comparison between the calculated and the observed differential conductance curves suggests that such quantum well structures could be designed as active regions for the generation of terahertz frequency radiation sources. © 1999 American Institute of Physics.
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73.50.Mx High-frequency effects; plasma effects
73.61.Ey III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
84.40.-x Radiowave and microwave (including millimeter wave) technology

Hierarchical design of quantum-dot cellular automata devices

Aaron Gin, Sara Williams, Haoyu Meng, and P. Douglas Tougaw

J. Appl. Phys. 85, 3713 (1999); http://dx.doi.org/10.1063/1.369737 (8 pages) | Cited 7 times

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We use hierarchical layout methods to combine fundamental quantum-dot cellular automata (QCA) devices into more complex devices, including a 2-to-1 multiplexer, a 4-to-1 multiplexer, and an eight-function bit-slice arithmetic logic unit (ALU). The ALU unit is implemented using 1245 cells, making it the largest QCA device ever designed and simulated. This hierarchical design method is possible because the Coulombic interaction between QCA cells is very local in nature. Since distant cells have very little effect on each other, the state of a cell can be very well approximated by considering only those cells that are near it. In a QCA device, nearby cells are usually part of the same functional unit, so we can design each functional unit separately, connect them with appropriate binary wires, and then simulate the entire device to verify its correct operation. © 1999 American Institute of Physics.
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84.30.Sk Pulse and digital circuits
84.40.Ua Telecommunications: signal transmission and processing; communication satellites
03.67.Lx Quantum computation architectures and implementations

Evidence of strong effect from the interface on the electrical characteristics of ZnSe/GaAs heterojunctions

D. Seghier, I. S. Hauksson, H. P. Gislason, K. A. Prior, and B. C. Cavenett

J. Appl. Phys. 85, 3721 (1999); http://dx.doi.org/10.1063/1.369738 (5 pages) | Cited 4 times

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The interface properties of ZnSe/GaAs heterojunctions grown by molecular beam epitaxy have been studied by electrical methods. The current–voltage and capacitance–voltage characteristics show a hysteresis which can be related to unusually slow current and capacitance transients in response to a change in the reverse bias. We performed admittance spectroscopy measurements at various frequencies in order to investigate this phenomenon. A large frequency dispersion of the capacitance and a broad peak in conductance spectra suggest the presence of interface states at the heterojunction between ZnSe and GaAs. We ascribe the long transients to slow changes in the charge on these interface states. We also propose that interface states result in a voltage-induced lowering of the barrier at the heterointerface. The capacitance versus frequency data were analyzed in terms of Lehovec’s model from which the density of interface states of 3–4×1012 cm−2 eV−1 were calculated. © 1999 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.20.At Surface states, band structure, electron density of states

Transport of alternating current and direct current by hard superconductors. Critical and resistive state

Alexander N. Ulyanov

J. Appl. Phys. 85, 3726 (1999); http://dx.doi.org/10.1063/1.369739 (6 pages) | Cited 3 times

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Voltage, voltage waveform, and losses in hard superconductors carrying alternating current (ac) and direct current (dc) transport current have been calculated in the framework of the critical and resistive state models for an arbitrary relation between the value of transport and critical current. The calculated results are in good agreement with the experimental ones. Voltage rectification by a superconductor carrying transport current, I(t) = Idc+Iac cos ωt, is explained. It is due to the shifting of the “working point” of the current–voltage (I–V) characteristic [point with coordinates current, jw = Idc, voltage, uw = f(Idc)] if the transport current contains a dc as well as an ac component. The peculiarities of the voltage across the superconductor with high value of the ac transport current versus time are predicted. © 1999 American Institute of Physics.
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74.25.F- Transport properties
74.25.Sv Critical currents
74.72.-h Cuprate superconductors

Flux penetration measurements and the harmonic magnetic response of hot isostatically pressed (Pb,Gd)Mo6S8

H. D. Ramsbottom and D. P. Hampshire

J. Appl. Phys. 85, 3732 (1999); http://dx.doi.org/10.1063/1.369740 (8 pages) | Cited 2 times

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Detailed flux penetration measurements and the harmonic magnetic response have been measured from 4.2 K up to the critical temperature in dc fields up to 10 T for a hot isostatically pressed Chevrel-phase superconductor (Pb,Gd)Mo6S8. Good agreement is found between experimental results up to the tenth harmonic and calculations derived from a critical-state model which demonstrates that on the macroscopic scale the supercurrents flow throughout the bulk of the material. The field and temperature dependence of the critical current density shows a universal scaling behavior in agreement with Kramer’s pinning law, which suggests that a single grain-boundary mechanism determines the critical current density. Complementary compositional microscopy, x-ray, resistivity, and susceptibility data are presented. When gadolinium is not incorporated into the crystal structure it acts primarily as an oxygen getter in the form Gd2S3, which enhances the density of paths of PbMo6S8 with low oxygen content and high superconducting critical parameters. When the divalent gadolinium replaces the trivalent lead to form (Pb1−xGdx)Mo6S8, it reduces the density of hole states at the Fermi energy which lowers the critical parameters, the critical current density, and the irreversibility field. © 1999 American Institute of Physics.
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74.70.Dd Ternary, quaternary, and multinary compounds (including Chevrel phases, borocarbides, etc.)
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Jb Electronic structure (photoemission, etc.)
74.25.Sv Critical currents
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
61.72.Mm Grain and twin boundaries

Intrinsic Josephson junctions in oxygen-deficient YBa2Cu3O7−δ film deposited on a substrate step

H. B. Wang, J. Chen, T. Tachiki, Y. Mizugaki, K. Nakajima, and T. Yamashita

J. Appl. Phys. 85, 3740 (1999); http://dx.doi.org/10.1063/1.369741 (5 pages) | Cited 10 times

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Using c-axis-oriented oxygen-deficient YBa2Cu3O7−δ film deposited across a low-angle step on a SrTiO3 substrate, we successfully demonstrated intrinsic Josephson effects. In addition to several voltage jumps of large amplitudes (a few millivolts) and remarkable hysteresis on the dc current–voltage curves, we observed upturns on the current–voltage curves under microwave irradiation which appeared at increasingly high voltages with increasing microwave power. We proposed to explain this observation in terms of high-order microwave-induced Shapiro steps. © 1999 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.50.+r Tunneling phenomena; Josephson effects
74.25.Sv Critical currents

High moment soft magnetic FeTiN thin films for recording head materials

H. Y. Wang, Y. J. He, Z. W. Ma, E. Y. Jiang, H. S. Huang, and W. H. Mao

J. Appl. Phys. 85, 3745 (1999); http://dx.doi.org/10.1063/1.369742 (4 pages) | Cited 8 times

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Soft magnetic properties and thermal stability of Fe–Ti–N alloys films have been investigated. Thin films with composition in the range of 8–10 at. % Ti, 10.5–14 at. % N, and balance Fe were prepared by reactive sputtering method. The films exhibit good soft magnetic properties in the as-deposited condition without any post heat treatment, e.g., low coercivity Hc ∼ 1.5 Oe, high permeability μ ∼ 3200 at 1 MHz and very high saturation magnetization 4πMs ∼ 24 kG. The thermal stability of these films was also found to be good, e.g., Hc was less than 2 Oe, and 4πMs was higher than 23 kG for the films annealed up to 500 °C. The high electrical resistivity ρ ∼ 100 μ Ω cm of the films can minimize the eddy current loss in the high frequency applications. The combination of high 4πMs and relatively high anisotropy field Ha ∼ 10 Oe in the film is conductive to the suppression of the undesirable ferromagnetic resonance interfere up to the GHz frequency range. © 1999 American Institute of Physics.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.70.-i Magnetic properties of thin films, surfaces, and interfaces
75.50.Ss Magnetic recording materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy

Microwave study of Nd0.7Sr0.3MnO3 thin film resistivity

J. R. Claycomb, N. Tralshawala, L.-M. Xie, J. Wosik, and J. H. Miller

J. Appl. Phys. 85, 3749 (1999); http://dx.doi.org/10.1063/1.369743 (4 pages)

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We report on microwave studies of Nd0.7Sr0.3MnO3 thin film losses in a shielded TE011 dielectric cavity. The cavity quality (Q) factor and resonant frequency are measured as a function of temperature with the dielectric cavity loaded with a thin film on a LaAlO3 substrate. A reference Q measurement is then made without the film enabling the extraction of the film-Q factor Qfilm. Here the temperature dependence of the Q factor is discussed in terms of resistive losses in the thin film. A numerical finite difference time domain code is then used to extract the microwave resistivity as a function of temperature from the measured Q factors. The numerical method involves the discretization of Maxwell’s equations on an axisymmetric space-time grid coupled to a discrete Fourier transform to determine the resonant frequency. © 1999 American Institute of Physics.
Show PACS
75.47.De Giant magnetoresistance
72.15.Gd Galvanomagnetic and other magnetotransport effects
77.22.Gm Dielectric loss and relaxation
77.65.Fs Electromechanical resonance; quartz resonators
75.47.Gk Colossal magnetoresistance
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