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15 Sep 1998

Volume 84, Issue 6, pp. 2989-3428

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Bistable behavior of a medium-deep center related to EL5 and EL6 in n-type bulk GaAs

Hiroyuki Shiraki, Yutaka Tokuda, and Koichi Sassa

J. Appl. Phys. 84, 3167 (1998); http://dx.doi.org/10.1063/1.368514 (8 pages) | Cited 8 times

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We report characteristic behaviors of medium-deep electron traps (EL5, EL6, etc.) in n-type bulk GaAs crystals observed by isothermal constant-capacitance–voltage transient spectroscopy (CCVTS). Each CCVTS spectrum of EL5 and EL6 was broader than a theoretical one expected for a single level, and was found to consist of more than two trap components. Anomalous filling time dependence of CCVTS peak heights for these traps was observed when the filling pulse width was varied in a wide range, i.e., one component of EL6 decreased to about 50% of its maximum, while one component of EL5 increased and saturated. The decrement of the constituent of EL6 was nearly equal to the increment of that of EL5. These variations could be reversed by controlling electron occupation fractions of these traps by means of changing the interval time between two adjacent filling pulses in application of the isothermal “double-pulse CCVTS” method. Such interaction was commonly observed in n-type bulk GaAs irrespective of carrier concentration and growth method. These behaviors of medium-deep electron traps are interpreted well by a model of an electronically controlled bistable reaction. © 1998 American Institute of Physics.
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72.80.Ey III-V and II-VI semiconductors
71.55.Eq III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Effects of oxygen-related defects on the leakage current of silicon p/n junctions

Yoshio Murakami, Yuhki Satoh, Hisashi Furuya, and Takayuki Shingyouji

J. Appl. Phys. 84, 3175 (1998); http://dx.doi.org/10.1063/1.368470 (12 pages) | Cited 7 times

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The reverse-bias leakage characteristics of silicon pn junctions have been investigated with particular attention to the effects of various types of oxygen-related defects, such as oxygen precipitates, oxidation induced stacking fault, and grown-in defects. The effects of oxygen-related defects on the leakage current of pn junctions in intrinsic gettering wafers and precipitation annealed wafers have been investigated quantitatively, and the field oxidation temperature used to form pn junctions has been found to be an important factor in determining the pn junction leakage current because oxygen-related defects are formed during low temperature field oxidation. It has also been found that grown-in oxidation induced stacking faults degrade the leakage characteristics. Grown-in defects that are well known to degrade the oxide breakdown characteristics were found to have some effects on the increase of the leakage current. In addition, it is recognized that the leakage current of pn junctions formed in wafers that have a relatively high concentration of interstitial oxygen has a transient component, caused by oxygen-related hole traps, which might also be the origin of the 1/f noise observed in pn junctions. © 1998 American Institute of Physics.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.80.Cw Elemental semiconductors
81.05.Cy Elemental semiconductors
73.20.Hb Impurity and defect levels; energy states of adsorbed species
81.65.Mq Oxidation
61.72.Yx Interaction between different crystal defects; gettering effect
81.65.Tx Gettering
64.75.-g Phase equilibria
61.72.Cc Kinetics of defect formation and annealing
61.72.Nn Stacking faults and other planar or extended defects
71.55.Cn Elemental semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.70.+m Noise processes and phenomena
61.72.J- Point defects and defect clusters

Hall effect and resistivity of β-FeSi2 thin films and single crystals

S. Brehme, P. Lengsfeld, P. Stauss, H. Lange, and W. Fuhs

J. Appl. Phys. 84, 3187 (1998); http://dx.doi.org/10.1063/1.368471 (10 pages) | Cited 13 times

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Cr-doped and undoped β-FeSi2 thin films were deposited on (001) and (111) Si substrates by molecular beam epitaxy. Single crystals were grown by the chemical vapor transport technique. In thin films we found a significant substrate influence on the Hall voltage at room temperature which was strongly reduced at lower temperatures. In Cr-doped samples a transition between defect-band conduction and valence-band conduction was observed in the temperature range 50–100 K. The behavior of the mobility curves μ(T) suggests that defect-band conduction dominates up to near room temperature in nominally undoped thin films. Below a sample-dependent temperature, being not higher than 150 K, often a nonlinear dependence of the Hall effect on the magnetic field was found, sometimes accompanied by pronounced hysteresis behavior. It is shown that this behavior is rather related to microinhomogeneities than to a magnetic phase transition. © 1998 American Institute of Physics.
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72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.Le Other inorganic semiconductors
72.80.Ga Transition-metal compounds

Molecular dynamics Monte Carlo simulations of grain boundary electron transport in n-silicon

R. P. Joshi and R. F. Wood

J. Appl. Phys. 84, 3197 (1998); http://dx.doi.org/10.1063/1.368472 (10 pages) | Cited 3 times

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Electron transport in Si low-angle bicrystals is analyzed by a novel Monte Carlo molecular dynamics simulation scheme. The effect of discrete charges at the grain boundaries is studied and compared to results from one-dimensional treatments. The average grain boundary charge density strongly influences transport, and a field-dependent threshold effect is predicted. Details of the internal charge arrangement are shown to be quite important at low fields and/or high grain boundary charge densities. Substantial increases in current conduction are predicted at lower temperatures over the thermionic emission model. Finally, analyses of interacting grain boundaries indicate site-correlation effects and a strong dependence of conductivity on the separation distance. © 1998 American Institute of Physics.
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72.80.Cw Elemental semiconductors
81.05.Cy Elemental semiconductors
61.72.Mm Grain and twin boundaries
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Polymer/metal interfaces and the performance of polymer light-emitting diodes

Jayesh M. Bharathan and Yang Yang

J. Appl. Phys. 84, 3207 (1998); http://dx.doi.org/10.1063/1.368473 (5 pages) | Cited 51 times

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Conjugated polymers are often treated as semiconductors with low doping concentrations. Unlike the traditional semiconductors which have a high density of surface states (mainly due to the dangling bonds), the nature of the metal/polymer interface, including barrier height and charge injection efficiency, is quite sensitive to the work function of the contact metal. In this article, we present evidence to show that the pinning of the surface Fermi level effect commonly observed at the silicon/metal interface can also be observed at the metal/polymer interface. It is achieved by controlling the doping level at the metal/polymer [poly(2-methoxy-5(2′-ethyl-hexyloxy)-1,4-phenylene vinylene) or MEH-PPV] interface. ITO/MEH-PPV/Al devices doped with 2 Å of calcium on the cathode side of the interfacial layer have the same device performance as the ITO/MEH-PPV/Ca devices. The heavily n-doped region pins the surface energy level, hence the polymer interface at the cathode side is no longer sensitive to the work function of the overcoated metal. It is believed that either the midgap bipolaron energy states created by the dopants or the sharp band bending at the interface is responsible for facilitating the electron injection. On the other hand, a p-doped region at the anode side, obtained by using a thin layer of an acid at the interface, pins the surface energy level and makes the contact insensitive to the work function of the anode. Therefore, an efficient polymer light-emitting diode with the p-i-n structure has been demonstrated without the matching of the work function of the metal electrodes. © 1998 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
73.40.Cg Contact resistance, contact potential
73.40.Ns Metal-nonmetal contacts
85.60.Jb Light-emitting devices
73.61.Ph Polymers; organic compounds

Noise in Al single electron transistors of stacked design

V. A. Krupenin, D. E. Presnov, M. N. Savvateev, H. Scherer, A. B. Zorin, and J. Niemeyer

J. Appl. Phys. 84, 3212 (1998); http://dx.doi.org/10.1063/1.368474 (4 pages) | Cited 29 times

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We have fabricated and examined several Al single electron transistors whose small islands were positioned on top of a counterelectrode and hence did not come into contact with a dielectric substrate. The equivalent charge noise figure of all transistors turned out to be surprisingly low, (2.5–7)×10−5e/math at f = 10 Hz. Although the lowest detected noise originates mostly from fluctuations of background charge, the noise contribution of the tunnel junction conductances was, on occasion, found to be dominant. © 1998 American Institute of Physics.
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85.35.Gv Single electron devices
72.70.+m Noise processes and phenomena

Space-charge influenced-injection model for conduction in Pb(ZrxTi1−x)O3 thin films

I. Stolichnov and A. Tagantsev

J. Appl. Phys. 84, 3216 (1998); http://dx.doi.org/10.1063/1.368888 (10 pages) | Cited 72 times

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A comprehensive study of leakage conduction in Pb(ZrxTi1−x)O3films with Pt electrodes is carried out. The conduction properties of films prepared in different ways (sol–gel coating, metalorganic chemical vapor deposition, sputtering) were studied by using different experimental techniques including variation of the applied voltage profile, photoassisted measurements, measurements at elevated temperatures, and variation of the prehistory of the samples. Based on the collective data, it is concluded that two different regimes of carrier injection (with the critical electric field of the crossover between these regimes being independent of the measuring technique) are responsible for true leakage conduction in Pt–Pb(ZrxTi1−x)O3–Pt films. A space-charge influenced-injection model is proposed for the interpretation of the experimental results obtained. This model describes well the main features of the observed current–voltage characteristics and provides a reasonable fit for the current–voltage curves measured at elevated temperatures, the values of the fitting parameters being in good agreement with the results of other studies. The true leakage current in the Pt–Pb(ZrxTi1−x)O3–Pt system is shown to be time dependent because of the influence of the injected charge entrapment during measurement. According to the present results, an activation energy of about 0.9 eV describes the temperature dependence of conduction in the range of 70–200 °C. It is shown that a possible origin of the crossover in the activation energy at the temperature range 120–140 °C widely reported in the literature can be a consequence of the measuring procedure. © 1998 American Institute of Physics.
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73.61.Ng Insulators
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
73.50.Fq High-field and nonlinear effects
77.80.-e Ferroelectricity and antiferroelectricity
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Ballistic electron emission microscopy study of barrier height inhomogeneities introduced in Au/n-Si Schottky contacts by a HF pretreatment

C. Detavernier, R. L. Van Meirhaeghe, R. Donaton, K. Maex, and F. Cardon

J. Appl. Phys. 84, 3226 (1998); http://dx.doi.org/10.1063/1.368475 (6 pages) | Cited 40 times

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The distribution of Schottky barrier heights over the contact area in Au/n-Si diodes was determined by ballistic electron emission microscopy. For samples on which an aqueous HF pretreatment of the Si substrate was applied, the histogram contains several high barrier Gaussian distribution components. After a short rinse, in de-ionized water or methanol, it was mainly the most important lower Gaussian component which was left. Using additional x-ray photoemission spectroscopy and atomic force microscopy measurements allowed us to propose a model, wherein negatively charged species containing F at the interface, are thought to be responsible for the high barrier Gaussian components. © 1998 American Institute of Physics.
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73.30.+y Surface double layers, Schottky barriers, and work functions
81.05.Cy Elemental semiconductors
81.65.-b Surface treatments
68.37.Vj Field emission and field-ion microscopy
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.60.Jv Interfaces; heterostructures; nanostructures
73.40.Ns Metal-nonmetal contacts
73.20.Hb Impurity and defect levels; energy states of adsorbed species
68.35.Ct Interface structure and roughness

Transport mechanisms in porous silicon

A. K. Ray, M. F. Mabrook, A. V. Nabok, and S. Brown

J. Appl. Phys. 84, 3232 (1998); http://dx.doi.org/10.1063/1.368476 (4 pages) | Cited 3 times

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The current transport mechanism through porous silicon (PS) films fabricated from 8 to 12 Ω cm p-type silicon (p-Si) substrates has been investigated using current–voltage I(V) measurements on metal/PS/p-Si/metal devices in the temperature range of 77–300 K. The characteristics for all devices show a rectifying behavior with ideality factor very close to unity. A value of 0.7 eV is obtained for the barrier height at the interface between PS and bulk p-Si at room temperature and the barrier height is found to increase with rising temperature. A band model is proposed in order to explain the observed characteristics. © 1998 American Institute of Physics.
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73.61.Cw Elemental semiconductors
73.40.Sx Metal-semiconductor-metal structures
73.40.Ei Rectification
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Energy-level alignment at interfaces between metals and the organic semiconductor 4,4′-N,N′-dicarbazolyl-biphenyl

I. G. Hill, A. Rajagopal, and A. Kahn

J. Appl. Phys. 84, 3236 (1998); http://dx.doi.org/10.1063/1.368477 (6 pages) | Cited 57 times

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We have used ultraviolet photoemission spectroscopy to study the formation of interfaces between the organic semiconductor, 4,4′-N,N′-dicarbazolyl-biphenyl (CBP), and the metals Au, Ag, and Mg. Each interface was studied by depositing the organic on the metal, and by depositing the metal on the organic. The two methods produced inequivalent interfaces, except in the case of Au/CBP. The position of the highest occupied molecular orbital relative to the Fermi level and the magnitude of the interface dipole were measured for each interface. The barrier to electron injection from each metal was estimated using the magnitude of the measured optical gap. An interface dipole, of magnitude nearly independent of the metal work function, was formed when CBP was deposited on a metal surface. The position of the Fermi level within the CBP gap was found to vary strongly with the metal work function. © 1998 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
79.60.Jv Interfaces; heterostructures; nanostructures
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Finite-element analysis of quantum wires with arbitrary cross sections

M. Ogawa, T. Kunimasa, T. Ito, and T. Miyoshi

J. Appl. Phys. 84, 3242 (1998); http://dx.doi.org/10.1063/1.368478 (8 pages) | Cited 9 times

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A finite-element method is developed for the analysis of eigenstates in the valence band of quantum wires which have arbitrary potential profiles. Our method is basically based on the Galerkin procedure and triangle linear elements are used as finite elements. In our formulation the effect of the band mixing in the valence band is duly taken into account. Boundary conditions at heterointerfaces are also taken into account in the multiband envelope function space. Numerical examples are presented for circular, square, rectangular, and triangular quantum wire structures. The relation is clarified between the degeneracy in the E-ky dispersion curve and the symmetricity of the confinement potential. © 1998 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
02.10.Ud Linear algebra
02.10.Xm Multilinear algebra
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
02.70.Dh Finite-element and Galerkin methods

The approximate analytic expressions for field dependence of surface impedance of high-Tc superconducting thin film in low- and intermediate-field region

B. B. Jin and R. X. Wu

J. Appl. Phys. 84, 3250 (1998); http://dx.doi.org/10.1063/1.368479 (4 pages) | Cited 4 times

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Assuming that a high-Tc superconducting thin film is composed of a network of superconducting grains connected by grain-boundary weak links, the equation describing its response under microwave current irf is solved using a perturbation method to the third order of irf. Based on the obtained results, analytic expressions for film’s microwave surface impedance are derived, revealing its dependence on a rf magnetic field in low and intermediate field limit. Good qualitative agreement with experiments is observed. © 1998 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.50.+r Tunneling phenomena; Josephson effects
61.72.Mm Grain and twin boundaries
74.25.F- Transport properties

Grain size dependence of the current–voltage characteristics and critical current density in the self-field approximation

A. Kiliç, K. Kiliç, and S. Senoussi

J. Appl. Phys. 84, 3254 (1998); http://dx.doi.org/10.1063/1.368480 (9 pages) | Cited 16 times

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In the self-field approximation, the influence of the grain radius on the current–voltage characteristics and associated critical current density Jc are investigated by considering the conventional flux flow motion of vortices. It is shown that the direct summation theory of Campbell et al. could be adopted to the granular systems [A. M. Campbell, J. E. Evetts, and D. Dew-Hughes, Philos. Mag. 10, 333 (1964)]. We found that Jc is enhanced as the size of the grains is decreased. The case of the critical current density being greater for smaller grains, which is consistent with both transport and low-field magnetization measurements is discussed by the weak links between the superconducting grains and also with the percolation model. © 1998 American Institute of Physics.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.20.De Phenomenological theories (two-fluid, Ginzburg-Landau, etc.)
74.25.Sv Critical currents

Propagation characteristics of a thin-film superconducting parallel-plate transmission line in the mixed state

Chien-Jang Wu

J. Appl. Phys. 84, 3263 (1998); http://dx.doi.org/10.1063/1.368481 (4 pages) | Cited 4 times

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The microwave propagation properties of a high Tc superconducting transmission line in the mixed state are theoretically investigated by using the electrodynamic field equations for a type-II superconductor developed by Coffey [J. Low Temp. Phys. 108, 331 (1997)]. We have numerically examined the attenuation constant and phase velocity as a function of temperature, frequency, and static magnetic field. The role played by the vortices in the superconducting transmission line is illustrated and discussed. © 1998 American Institute of Physics.
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85.25.-j Superconducting devices
84.40.Az Waveguides, transmission lines, striplines
74.78.-w Superconducting films and low-dimensional structures
74.25.Op Mixed states, critical fields, and surface sheaths
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)

Magnetic-domain structure of Nd2Fe14B permanent magnets

Yimei Zhu and M. R. McCartney

J. Appl. Phys. 84, 3267 (1998); http://dx.doi.org/10.1063/1.368515 (6 pages) | Cited 8 times

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We report our studies of magnetic-domain structure in Nd2Fe14B permanent magnets using advanced transmission and scanning electron microscopy, including Lorentz imaging and electron holography. Domain-wall spacing D was measured as a function of thickness t for thin crystals, and also wall width of 90° and 180° domains; the domain-wall energies were calculated. Orientation and field dependence of the domain configuration and domain-wall behavior were examined in situ under different temperatures and applied fields. Characteristic magnetic structural features unique to corresponding bulk samples, such as reversed spike-domains and undulating domain boundaries, were also investigated. © 1998 American Institute of Physics.
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75.50.Bb Fe and its alloys
75.50.Ww Permanent magnets
75.60.Ch Domain walls and domain structure

Effect of [111] texture on the perpendicular magnetic anisotropy of Co/Ni multilayers

V. M. Naik, S. Hameed, R. Naik, L. Pust, L. E. Wenger, G. L. Dunifer, and G. W. Auner

J. Appl. Phys. 84, 3273 (1998); http://dx.doi.org/10.1063/1.368482 (5 pages) | Cited 5 times

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[111]fcc oriented [Co(2 Å)/Ni(7 Å)]20 multilayers were prepared by molecular beam epitaxy at room temperature on epitaxial Au/Ag buffer layers grown on chemically etched Si(111) surfaces. NH4F etching of Si(111) leads to a smaller spread in the 〈111〉 orientation of the Au/Ag buffer layers and the Co/Ni multilayers as compared to a similar sample prepared on HF-etched Si(111). This results in a stronger perpendicular magnetic anisotropy as determined from the magnetic hysteresis loops. Cross-sectional transmission electron microscopy studies show that the magnetic multilayer film is not flat but has significant waviness at both top and bottom surfaces. The observed waviness originates in part from the waviness already present on the surface of the Au buffer layer and appears to be further enhanced by the difference in the surface free energies of Au and the magnetic elements. A flatter Au/Ag buffer layer is essential to further improve the [111] texture of the [Co/Ni] multilayers. © 1998 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
68.35.Ct Interface structure and roughness
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Cc Other ferromagnetic metals and alloys

Magnetization of a trilayer structure with alternate in-plane and out-of-plane anisotropies

Takehiko Yorozu and Xiao Hu

J. Appl. Phys. 84, 3278 (1998); http://dx.doi.org/10.1063/1.368483 (27 pages) | Cited 1 time

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Both analytical and numerical calculations are carried out in order to determine the equilibrium magnetization configuration in trilayer magnetic materials having an in-plane anisotropy defect sandwiched in between perpendicular anisotropy layers. By varying the applied fields, the configuration follows the state where the sum of anisotropy, exchange, and Zeeman energy becomes minimum. The magnetization reversal occurs abruptly at increased field which either corresponds to nucleation or pinning coercivity. It is also shown that these coercivity values depend on the thickness of the in-plane layer. An explicit analytical solution can be derived for the extreme case in the upper and lower bounds of in-plane defect layer thickness, i.e., in the case for null and infinitive in-plane layer thickness. The results are compared with the previous data reported for systems having a perpendicular anisotropy defect layer. © 1998 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy

Effect of silicon substitution on the magnetic properties of Tb2Fe17 single crystals

J. Du, G. H. Wu, C. C. Tang, Y. X. Li, and W. S. Zhan

J. Appl. Phys. 84, 3305 (1998); http://dx.doi.org/10.1063/1.368484 (6 pages) | Cited 3 times

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The growth of single crystals Tb2Fe17−xSix (x = 0, 1, 2, 3, and 3.3) by the Czochralski method is performed. The crystal structure and magnetic properties are investigated. The substitution of silicon for iron leads to the reduction of the lattice parameters, and the significant increase of the Curie temperature from 413 to 526 K. The mean field analysis shows that the Fe–Fe exchange interaction is much strengthened while the Tb–Fe one is slightly weakened by the introduction of silicon. The anisotropy constants up to the sixth order are calculated by fitting the magnetization process of the samples at 1.5 K under the field up to 65 kOe. In addition, a narrow domain wall pinning-dominated process caused by the substitution of Si for Fe is confirmed and analyzed. © 1998 American Institute of Physics.
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75.50.Bb Fe and its alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.66.Dk Alloys
75.30.Gw Magnetic anisotropy
71.70.Gm Exchange interactions
75.30.Et Exchange and superexchange interactions
61.50.Lt Crystal binding; cohesive energy
81.10.Fq Growth from melts; zone melting and refining

Structural and magnetic properties of the Ti/Fe multilayers

A. Fnidiki, J. Juraszek, J. Teillet, N. H. Duc, T. M. Danh, M. Kaabouchi, and C. Sella

J. Appl. Phys. 84, 3311 (1998); http://dx.doi.org/10.1063/1.368485 (6 pages) | Cited 5 times

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The structure and magnetic properties of the rf-sputtered Fe/Ti multilayers with the fixed Ti-layer thicknesses (series 1: tTi = 1 nm and series 2: tTi = 2 nm) and the variable Fe-layer thicknesses (1 nm ⩽ tFe ⩽ 6 nm) have been studied by the high-angle x-ray diffraction, transmission electron microscopy, conversion electron Mössbauer spectrometry and vibrating sample magnetometer. The results show that Fe layers with thicknesses less than 1 nm are alloyed forming an amorphous TiFe2 phase. As the Fe-layer thickness increases, the iron-rich crystalline Fe–Ti alloy is formed at the interface and, finally, the pure crystalline α-Fe and Ti layers appear in the center of the individual subsystems. The spin orientation in Fe layers is then strongly aligned in the film plane. However, in the interfacial region, perpendicular spin orientation is evidenced. This perpendicular magnetic anisotropy is associated to the Fe-rich alloy at the interface and is discussed in terms of reduced symmetry effects on the band structure of the 3d(Fe)-itinerant electrons. © 1998 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
76.80.+y Mössbauer effect; other γ-ray spectroscopy
75.30.Gw Magnetic anisotropy
81.15.Cd Deposition by sputtering
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
75.10.Lp Band and itinerant models

Magnetic properties and microstructure of amorphous Co100−xTbx thin films

P. C. Kuo and Chih-Ming Kuo

J. Appl. Phys. 84, 3317 (1998); http://dx.doi.org/10.1063/1.368486 (5 pages) | Cited 6 times

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Amorphous Co100−xTbx alloy thin films with the composition of x = 7–60 at. % were prepared by dc magnetron sputtering at various powers and argon pressures then annealing in vacuum. Effects of the composition, sputtering power, argon pressure, and annealing temperature on the parallel and normal to the film plane magnetic properties have been investigated. The analysis of transmission electron microscopy diffraction patterns and magnetic measurement data indicate that an amorphous film with isotropic magnetic properties can be produced after low temperature annealing. The maximum observed perpendicular coercivity was as high as 6000 Oe for the as-deposited Co–Tb amorphous films. A nearly magnetically isotropic amorphous Co–Tb film with in-plane coercivity of about 2080 Oe was obtained after annealing. © 1998 American Institute of Physics.  
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75.50.Gg Ferrimagnetics
75.50.Ss Magnetic recording materials
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
81.05.Bx Metals, semimetals, and alloys
61.43.Dq Amorphous semiconductors, metals, and alloys
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Temperature dependence of conventional and effective pyroelectric coefficients for compositionally graded BaxSr1−xTiO3 films

Majed S. Mohammed, Gregory W. Auner, Ratna Naik, Joseph V. Mantese, Norman W. Schubring, Adolph L. Micheli, and Antonio B. Catalan

J. Appl. Phys. 84, 3322 (1998); http://dx.doi.org/10.1063/1.368516 (4 pages) | Cited 67 times

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Ferroelectric thin films (∼1.2 μm) of BaxSr1−xTiO3 with gradients in composition normal to the growth surface were formed on platinum substrates by metalorganic decomposition. Effective (pseudo) pyroelectric coefficients as large as 0.06 μC/cm2 K have been obtained from these active ferroelectric devices under the application of an ac field (charge pumping). In contrast, a value of only −0.003 μC/cm2 K has been measured for the conventional pyroelectric coefficient. © 1998 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
77.70.+a Pyroelectric and electrocaloric effects
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Nonlinear behavior of thin film SrTiO3 capacitors at microwave frequencies

A. B. Kozyrev, T. B. Samoilova, A. A. Golovkov, E. K. Hollmann, D. A. Kalinikos, V. E. Loginov, A. M. Prudan, O. I. Soldatenkov, D. Galt, C. H. Mueller, T. V. Rivkin, and G. A. Koepf

J. Appl. Phys. 84, 3326 (1998); http://dx.doi.org/10.1063/1.368487 (7 pages) | Cited 53 times

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The voltage-dependent dielectric constant (ϵ) of SrTiO3 (STO) thin films is the basis for developing cryogenic capacitors for tunable microwave applications. In this study, the effect of microwave signal level on nonlinear response at 1.7–1.9 GHz was examined by measuring the level of the third order intermodulation distortion (IMD) signal relative to the input signal level. Small signal dielectric properties such as capacitance, tuning, and loss (tan δ) were also measured at 1 MHz, 3 GHz, and 10 GHz, at temperatures from 4.2 to 300 K. Planar capacitors were comprised of highly (100)-oriented, 1 μm thick STO films deposited via magnetron sputtering onto CeO2-buffered (1102)-oriented sapphire substrates, with 10 μm gaps between the electrodes. Deviations from the anticipated cubic dependence of the third order IMD product on incident power, for incident power ranges from −10 to 22 dBm, were attributed to conductivity nonlinearity. At incident power levels of 22 dBm and with no dc bias applied to the capacitor, the level of the third order IMD product was 21 dB below the fundamental signal level. Application of a 107 V/m dc electric field bias across the capacitor suppressed the third order IMD by an additional 10 dB. The nonlinear properties of thin film STO capacitors as a function of microwave voltage were determined by comparing the experimental and theoretical dependencies of the IMD products. © 1998 American Institute of Physics.
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84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation
84.40.Az Waveguides, transmission lines, striplines
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Changes in the photoelectrical properties and generation of photoinduced defects under light/air exposure of C60 thin films

E. A. Katz, D. Faiman, B. Mishori, Yoram Shapira, A. I. Shames, S. Shtutina, and S. Goren

J. Appl. Phys. 84, 3333 (1998); http://dx.doi.org/10.1063/1.368488 (5 pages) | Cited 13 times

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We report on the time development of surface photovoltage (SPV) and electron paramagnetic resonance (EPR) spectra for C60 films irradiated by room light in air. Such exposure is shown to result in the progressive reduction of the SPV signal at 0.9–1.1 eV and in an increase in the signal at approximately 1.3 eV, as well as in the reduction of the signals at about 1.6 and 2.3 eV. A decrease in the dark contact potential difference signal as a result of surface band-bending reduction is also observed after exposure. These results are explained assuming that gap states at Ec−(0.9–1.1) eV in our samples are attributed to nonbonded intercalated O2 in the C60 lattice while other states at Ev+1.3 eV are related to oxygen chemically bonded to the C60 molecules. EPR measurements reveal that light/air exposure causes an increase in the number of C60+ paramagnetic defects. A hypothesis has been suggested that the recombination centers at Ev+1.3 eV and the C60+ paramagnetic centers have the same origin and are attributable to carbon dangling bonds. © 1998 American Institute of Physics.
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73.61.Wp Fullerenes and related materials
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.50.Pz Photoconduction and photovoltaic effects
73.40.Cg Contact resistance, contact potential
76.30.Mi Color centers and other defects
71.20.Tx Fullerenes and related materials; intercalation compounds

Negative peaks in photocurrent spectra of thick barrier GaAs/AlAs multiple quantum wells

K. Kawasaki, M. Imazawa, K. Kawashima, K. Fujiwara, M. Hosoda, and K. Tominaga

J. Appl. Phys. 84, 3338 (1998); http://dx.doi.org/10.1063/1.368489 (4 pages)

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We have experimentally studied photocurrent (PC) spectral features of a relatively thick barrier multiple quantum well (MQW) p-i-n diode at 18 and 80 K as a function of axial electric field. It is found that PC spectra do not always reflect the photoabsorption spectral line shape under the low field condition and show negative peaks at the exciton resonance wavelengths. These PC dips are qualitatively explained by considering the distribution of photogenerated carriers within the intrinsic region and competition between carrier transit and recombination times. Furthermore, the dominance of electron-tunneling transport for the low temperature PC mechanism explains enhanced negative peaks in the PC spectra at 80 K when the tunneling assisted drift is reduced. © 1998 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors
73.61.Ey III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.35.-y Excitons and related phenomena
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Self-assembled InAs/GaAs quantum dots studied with excitation dependent cathodoluminescence

Y. Tang, D. H. Rich, I. Mukhametzhanov, P. Chen, and A. Madhukar

J. Appl. Phys. 84, 3342 (1998); http://dx.doi.org/10.1063/1.368490 (7 pages) | Cited 21 times

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We have examined the optical properties of self-assembled InAs quantum dots (QDs) with polarization sensitive and time-resolved cathodoluminescence (CL) techniques. The InAs QDs were formed via self-assembly during molecular beam epitaxial growth of InAs on unpatterned GaAs(001). CL spectra exhibited a two-component line shape whose linewidth, intensity, and peak positions were found to be temperature and excitation dependent. The two components are found to be consistent with state filling of the QDs, resulting in emission involving ground state and excited state excitonic transitions. The luminescence intensities and lineshapes of the QD and wetting layer (WL) excitonic transitions were analyzed with constant excitation and time-resolved CL for various temperatures and excitation levels to study the thermal activation, re-emission, and recombination kinetics of carriers. Thermal quenching of the QD ground state and excited state components in the 105–175 K range is correlated with a rise in the WL emission, showing that the WL carrier distribution is fed partially by thermal reemission of carriers from the QDs. A more rapid thermal quenching of the QD and WL excitonic emissions in the 185–300 K range is consistent with thermal reemission of carriers into the GaAs matrix. Time delayed CL spectra show that carriers in the excited states rapidly feed the ground state during the decay phase of the luminescence, further confirming that the two components are derived from the same QD. The CL decay time for the QD luminescence was found to be wavelength and temperature dependent, owing to thermal reemission into the WL. The CL decay times ranged from 0.1 to 2.0 ns. A polarization anisotropy was found in CL spectroscopy, revealing the importance of the stress anisotropy in both the formation of QDs and their subsequent optical emission. © 1998 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.60.Hk Cathodoluminescence, ionoluminescence
78.66.Fd III-V semiconductors
71.35.-y Excitons and related phenomena
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.47.-p Spectroscopy of solid state dynamics
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