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15 Dec 2000

Volume 88, Issue 12, pp. 6973-7369

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Highly erbium-doped zinc–oxide thin film prepared by laser ablation and its 1.54 μm emission dynamics

Shuji Komuro, Tooru Katsumata, Takitaro Morikawa, Xinwei Zhao, Hideo Isshiki, and Yoshinobu Aoyagi

J. Appl. Phys. 88, 7129 (2000); http://dx.doi.org/10.1063/1.1326470 (8 pages) | Cited 42 times

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Erbium-doped ZnO (ZnO:Er) thin films were fabricated by the KrF excimer laser ablation technique, which is a useful and simple technique to dope Er atoms on the order of 1020 cm−3 into a host material. As-prepared ZnO:Er films showing strong c-axis orientation with a hexagonal crystalline structure indicate a low electrical resistivity of 6.4×10−3 Ω cm. The sharp and intense photoluminescence (PL) at 1.54 μm originating from the intra-4f transition in the Er3+ ions as well as PL in UV region from the ZnO host were observed even at room temperature. Significant distinction arising from the different Er emission centers responsible for the 1.54 μm emission cannot be found in the temperature dependence between the ZnO:Er and Si:Er film as a reference, except for the PL spectrum feature and main PL peak position. This result suggests the existence of Er emission centers in ZnO:Er and Si:Er films that are different from each other. The details of Er-related 1.54 μm emission dynamics of ZnO:Er films have been investigated for the different excitation conditions, where the Er3+ ions have been excited either through a carrier-mediated process in the ZnO host, or through direct pumping into the 4f energy level of the Er3+ ions. There is no change in the 1.54 μm PL spectrum feature in spite of the different excitation conditions, whereas a sensible change can be seen in the rise time of the 1.54 μm emission. The shorter rise time of the 1.54 μm emission observed for indirect excitation implies an excitation efficiency superior to the direct excitation of Er3+ ions. This result indicates that the ZnO:Er thin films are expected to be a promising infrared optoelectronic materials candidate for carrier injection devices because of the high electrical conductivity and high excitation efficiency of the Er3+ ions of an electron–hole-mediated process resulting from ZnO host excitation. © 2000 American Institute of Physics.
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78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
71.55.Gs II-VI semiconductors

Optical properties of substituted phthalocyanine rare-earth metal complexes

K. Yoshino, S. B. Lee, T. Sonoda, H. Kawagishi, R. Hidayat, K. Nakayama, M. Ozaki, K. Ban, K. Nishizawa, K. Ohta, and H. Shirai

J. Appl. Phys. 88, 7137 (2000); http://dx.doi.org/10.1063/1.1316050 (7 pages) | Cited 11 times

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Comparative study of optical properties of alkylthio-group-substituted phthalocyanine rare-earth metal sandwich complexes ([(CnS)8Pc]2M,M=Eu,Lu,Tb) is presented. Photoluminescence and photoconductivity of [(CnS)8Pc]2M complex is very weak. Two photoluminescence bands were observed at around 400–650 and 720–800 nm in chloroform solution corresponding to the Soret and Q bands in the absorption spectra, respectively. However, the emission from Eu3+ ion (as well as Tb3+) was not found compared with other Eu complexes because the 5d levels of the Eu3+ ion lie higher than the triplet level of the ligand. The significant enhancement of the photoconductivity of [(C16S)8Pc]2M after C60 doping is reported. The photoconductivity is positive at the low electric field in the ohmic regime while it becomes negative at the high electric field upon photoexcitation with strongly absorbed light. The negative photoconductivity is attributed to space-charge effects. The mechanism of photoluminescence and photoconductivity are discussed by taking the electronic energy schemes of phthalocyanine ligands and lanthanide ion and C60 into consideration. © 2000 American Institute of Physics.
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78.55.Kz Solid organic materials
72.40.+w Photoconduction and photovoltaic effects
77.22.Jp Dielectric breakdown and space-charge effects

Donor–acceptor pair recombination in gallium sulfide

A. Aydinli, N. M. Gasanly, and K. Gökşen

J. Appl. Phys. 88, 7144 (2000); http://dx.doi.org/10.1063/1.1323515 (6 pages) | Cited 20 times

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Low temperature photoluminescence of GaS single crystals shows three broad emission bands below 2.4 eV. Temperature and excitation light intensity dependencies of these bands reveal that all of them originate from close donor–acceptor pair recombination processes. Temperature dependence of the peak energies of two of these bands in the visible range follow, as expected, the band gap energy shift of GaS. However, the temperature dependence of the peak energy of the third band in the near infrared shows complex behavior by blueshifting at low temperatures followed by a redshift at intermediate temperatures and a second blueshift close to room temperature, which could only be explained via a configuration coordinate model. A simple model calculation indicates that the recombination centers are most likely located at the nearest neighbor lattice or interstitial sites. © 2000 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
61.72.J- Point defects and defect clusters

Asymmetric peak line shape of infrared dielectric function spectra for thermally grown silicon dioxide films

Kenji Ishikawa, Kunihiro Suzuki, and Shigeru Okamura

J. Appl. Phys. 88, 7150 (2000); http://dx.doi.org/10.1063/1.1325377 (7 pages) | Cited 8 times

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Measured infrared dielectric function spectra ranging from 300 to 1400 cm−1 for thermally grown silicon dioxide films were studied. The dielectric function spectra were calculated by requiring the calculated spectra to fit to the actual spectra. The peak line shape of the dielectric function can be described by a Gaussian distribution, but not by a Lorentzian line shape. In detail, frequencies of half height for the imaginary part of the dielectric function of high- and low-frequency edges are not actually symmetrical. According to interpretations based on a central and noncentral force network model, the asymmetric distribution of the dielectric function arises from the symmetrical distribution of the bond angles of a random network of the SiO4 tetrahedra. For that reason, we developed a dielectric function model which can describe an asymmetrical Gaussian line shape. This asymmetric Gaussian model minimizes the number of parameters needed, which are the one center position and low- and high-Gaussian distribution widths, compared with the assignment method for multiple purely Gaussian peaks. © 2000 American Institute of Physics.
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78.30.Hv Other nonmetallic inorganics
78.66.Nk Insulators
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
77.22.Ch Permittivity (dielectric function)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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Band gap and lattice constant of GaxIn1−xAsySb1−y

Kyurhee Shim, Herschel Rabitz, and Partha Dutta

J. Appl. Phys. 88, 7157 (2000); http://dx.doi.org/10.1063/1.1323520 (5 pages) | Cited 10 times

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The energy band gap and lattice constant of the quaternary alloy GaxIn1−xAsySb1−y were determined over the entire composition space (x,y) using a correlated function expansion (CFE) technique to interpolate from observed ternary compound data. Considerable anomalous band gap behavior (i.e., deep bowing) was found, which produced band gap minima as a function of composition. This deep bowing effect was experimentally observed in a quasibinary alloy (GaSb)1−z(InAs)z at low values of z. In addition, the CFE lattice matching relations of the alloy grown on GaSb and InAs were obtained as a function of composition, and the corresponding band gaps were estimated. The CFE estimates were in good agreement with existing experimental data. © 2000 American Institute of Physics.
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71.20.Nr Semiconductor compounds
61.66.Fn Inorganic compounds

Carrier transfer in self-assembled coupled InAs/GaAs quantum dots

G. G. Tarasov, Yu. I. Mazur, Z. Ya. Zhuchenko, A. Maaßdorf, D. Nickel, J. W. Tomm, H. Kissel, C. Walther, and W. T. Masselink

J. Appl. Phys. 88, 7162 (2000); http://dx.doi.org/10.1063/1.1323516 (9 pages) | Cited 35 times

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Photoluminescence (PL) spectra and time-resolved PL data from AlGaAs/GaAs superlattice structures containing thin InAs layers of about 1–3 monolayer grown on semi-insulating (001)-oriented GaAs substrates at lowered temperatures are studied. The size distribution of InAs quantum dots (QDs) among different families (modes) is controlled by variation of growth temperature and/or growth interruption. We demonstrate the stabilization of the PL magnitude caused by strong coupling between different modes and the full width at half maximum of “large size” QD modes within a certain temperature interval (50–150 K) due to feeding of the radiative transitions from nonradiative decay and carrier transfer arising from decaying excitonic states of the small size QD modes. Strong competition between different channels of ground state relaxation leads to an oscillating dependence of the PL transient for the small size QD mode. Efficient inter- and intramode tunneling rules out “bottleneck restrictions” for the PL. The parameters of intra- and intermode tunneling are determined from time-resolved PL. © 2000 American Institute of Physics.
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73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.47.-p Spectroscopy of solid state dynamics
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.35.-y Excitons and related phenomena

Quantum-confined Stark effects of InAs/GaAs self-assembled quantum dot

Shu-Shen Li and Jian-Bai Xia

J. Appl. Phys. 88, 7171 (2000); http://dx.doi.org/10.1063/1.1329354 (4 pages) | Cited 16 times

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Quantum-confined Stark effects in InAs/GaAs self-assembled quantum dots are investigated theoretically in the framework of effective-mass envelope function theory. The electron and hole energy levels and optical transition energies are calculated in the presence of perpendicular and parallel electric field. In our calculation, the effect of finite offset, valence band mixing, and strain are all taken into account. The results show that the perpendicular electric field weakly affects the electron ground state and hole energy levels. The energy levels are affected strongly by the parallel electric field. For the electron, the energy difference between the ground state and the first excited state decreases as electric field increases. The optical transition energies have clear redshifts in electric field. The theoretical results agree well with the available experimental data. Our calculated results are useful for the application of quantum dots to photoelectric devices. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.20.Jq Electro-optical effects
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Deep-level impurities in CdTe/CdS thin-film solar cells

A. Balcioglu, R. K. Ahrenkiel, and F. Hasoon

J. Appl. Phys. 88, 7175 (2000); http://dx.doi.org/10.1063/1.1326465 (4 pages) | Cited 13 times

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We have studied deep-level impurities in CdTe/CdS thin-film solar cells by capacitance–voltage (C–V), deep-level transient spectroscopy (DLTS), and optical DLTS (ODLTS). CdTe devices were grown by close-spaced sublimation. Using DLTS, a dominant electron trap and two hole traps were observed. These traps are designated as E1 at EC−0.28 eV, H1 at EV+0.34 eV, and H2 at EV+0.45 eV. The presence of the E1 and H1 trap levels was confirmed by ODLTS. The H1 trap level is due to Cu-induced substitutional defects. The E1 trap level is believed to be a deep donor and is attributed to the doubly ionized interstitial Cu or a Cu complex. The E1 trap is an effective recombination center and is a lifetime killer. © 2000 American Institute of Physics.
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73.61.Ga II-VI semiconductors
81.05.Dz II-VI semiconductors
84.60.Jt Photoelectric conversion
73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Diffusing species in the proton generation process in Si/SiO2/Si structures

V. Girault

J. Appl. Phys. 88, 7179 (2000); http://dx.doi.org/10.1063/1.1287413 (8 pages)

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In this article, a study of the proton generation in Si/separation by implantation of oxygen (SIMOX) SiO2/Si structures is reported. The interest was focused on the ability to create mobile charges in SIMOX oxides following a forming gas anneal composed of 92% of N2 and 8% of H2 at 700 °C. The kinetics of the charge generation at 700 °C are presented for two SIMOX oxide thicknesses. A study of the influence of the forming gas pressure is also reported. From both types of experiments, it was concluded that the charge generation mechanism is an interface controlled reaction and that molecular hydrogen H2 or atomic hydrogen H are not the limiting diffusing species in the charge generation. By varying the pressure of the forming gas atmosphere, it was shown that the charge generation is dependent on the square root of the forming gas pressure. From these results and other authors’ work, a model is proposed in which the proton generation is a two-step process. © 2000 American Institute of Physics.
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73.40.Ty Semiconductor-insulator-semiconductor structures
81.05.Cy Elemental semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.72.uf Ge and Si
85.40.Ry Impurity doping, diffusion and ion implantation technology
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Energy level alignment in organic-based three-layer structures studied by photoelectron spectroscopy

G. Greczynski, Th. Kugler, and W. R. Salaneck

J. Appl. Phys. 88, 7187 (2000); http://dx.doi.org/10.1063/1.1328059 (5 pages) | Cited 14 times

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The alignment of energy band edges at interfaces in three-layer structures, important in polymer-based electroluminescent devices, have been studied using photoelectron spectroscopy. Careful choice of the materials allows investigation of the role of the substrate work function. These results are in agreement with the energy level diagram commonly assumed for the metal/polymer/metal structure, with the potential drop over the polymer layer being equal to the difference between the work functions of the metal contacts. Direct indication of the alignment of the electrochemical potential across the three-layer structure has been observed by photoelectron spectroscopy. © 2000 American Institute of Physics.
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79.60.Fr Polymers; organic compounds
79.60.Jv Interfaces; heterostructures; nanostructures
73.40.Cg Contact resistance, contact potential
73.20.At Surface states, band structure, electron density of states
85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.66.Qn Polymers; organic compounds

Characterization of magnetron sputtering deposited thin films of TiN for use as a metal electrode on TiN/SiO2/Si metal–oxide–semiconductor devices

E. K. Evangelou, N. Konofaos, X. A. Aslanoglou, C. A. Dimitriadis, P. Patsalas, S. Logothetidis, M. Kokkoris, E. Kossionides, R. Vlastou, and R. Groetschel

J. Appl. Phys. 88, 7192 (2000); http://dx.doi.org/10.1063/1.1322068 (5 pages) | Cited 6 times

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Titanium nitride (TiN) thin films were deposited by dc magnetron sputtering on SiO2/n-Si substrates in order to study their use as gate electrodes in metal–oxide–semiconductor (MOS) devices. Rutherford backscattering spectroscopy was used to determine the composition of the films and the results were correlated to those obtained by electrical measurements of the constructed MOS devices. Oxygen contamination of the TiN layers was observed, with percentage and spatial variations depending on the various deposition parameters such as the deposition temperature and the substrate bias. The best electrical performance was achieved for devices where the exposed TiN surface had low oxygen contamination. From these samples, the TiNx–Si barrier height was calculated to be equal to 0.52 eV. © 2000 American Institute of Physics.
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81.15.Cd Deposition by sputtering
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
73.40.Ns Metal-nonmetal contacts

X-ray induced modification of electronic properties of boron nitride thin films

V. Ageev, M. Ugarov, V. Frolov, A. Karabutov, E. Loubnin, N. Badi, and A. Bensaoula

J. Appl. Phys. 88, 7197 (2000); http://dx.doi.org/10.1063/1.1312837 (4 pages)

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X-ray induced modification of the electronic properties of nanocrystalline boron nitride (BN) films with different compositions and carbon impurity contents is reported. The related changes of the surface composition and valence band structures of the irradiated films are discussed. X-ray irradiation of nanocrystalline BN films is shown to widen areas with intermediate values of electroconductivity (associated with areas of high emission density) and to increase the average value of electroconductivity by redistributing surface potentials and electron emission sites. Improvement of the field emission is observed with both increasing electron current and diminishing thresholds. Longer x-ray irradiation times yield greater improvement. © 2000 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
73.61.Ey III-V semiconductors
73.25.+i Surface conductivity and carrier phenomena
61.80.Cb X-ray effects
61.82.Fk Semiconductors
61.82.Rx Nanocrystalline materials
68.35.Dv Composition, segregation; defects and impurities
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
71.20.Nr Semiconductor compounds

Electrical conduction in epitaxial BeSeTe/Si

Kevin Clark, Eduardo Maldonado, Pedro Barrios, Gregory F. Spencer, Robert T. Bate, and Wiley P. Kirk

J. Appl. Phys. 88, 7201 (2000); http://dx.doi.org/10.1063/1.1322598 (4 pages) | Cited 4 times

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Epitaxial wide-band gap II–VI beryllium chalcogenide semiconductor films BeTe, BeSe, and BeSeTe were grown on arsenic-terminated silicon substrates. Electrical characteristics of Schottky contacts to the films were measured. Current-temperature measurements at elevated temperatures showed conduction band offsets of 1.2 eV for the BeSe0.41Te0.59/As/Si and 1.3 eV for the BeSe/As/Si heterostructures. At room temperature, the current density through BeSe/Si and BeSe0.41Te0.59/Si films was mid-10−9 A/cm2 at 0.1 MV/cm, similar to previously reported values for ZnS/Si, while BeTe/Si films had orders of magnitude higher current density possibly due to interfacial recombination. © 2000 American Institute of Physics.
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73.61.Ga II-VI semiconductors
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.20.At Surface states, band structure, electron density of states
73.30.+y Surface double layers, Schottky barriers, and work functions

Resistance and tunneling spectra of aligned multiwalled carbon nanotube arrays

D. N. Davydov, J. Li, K. B. Shelimov, T. L. Haslett, M. Moskovits, and B. W. Statt

J. Appl. Phys. 88, 7205 (2000); http://dx.doi.org/10.1063/1.1318392 (4 pages) | Cited 18 times

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The resistance and tunneling spectra of samples formed by depositing silver electrodes at the two ends of aligned, template-grown, carbon nanotube arrays were measured in the temperature range 0.67–440 K. Two types of samples were fabricated, one with small oxide tunnel junctions separating the carbon nanotubes from the metal electrodes, the other with a significant Al2O3 tunnel barrier. The measurements indicate the presence of three regimes for dI/dV(V). For T>220 K, dI/dV(V) and the zero-bias conductivity show a broad minimum and an activation temperature dependence suggesting semiconductor behavior. In the temperature range 10<T<140 K, the zero-bias conductivity shows a square-root temperature dependence. For T<2 K, a very steep rise in the zero-bias tunneling resistance is observed with a strong simultaneous suppression of the tunneling conductivity near the Fermi energy. Coulomb blockade is suggested as a plausible explanation of the observed behavior. © 2000 American Institute of Physics.
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73.23.Hk Coulomb blockade; single-electron tunneling
73.61.Wp Fullerenes and related materials
73.61.Cw Elemental semiconductors
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Magnetic properties of Co–P powders produced by chemical reduction

T. Saito, M. Igarashi, and M. Kobayashi

J. Appl. Phys. 88, 7209 (2000); http://dx.doi.org/10.1063/1.1327290 (4 pages) | Cited 8 times

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Co–P powders were produced by chemical reduction. The powders had a spherical shape with an average diameter of about 1 μm. X-ray diffraction and differential scanning calorimetry studies confirmed that the powders were amorphous. The amorphous powders showed higher saturation magnetization than the crystalline counterparts. Heat treatment of the powders above the crystallization temperature resulted in the formation of fcc Co, hcp Co, and Co2P phases. The saturation magnetization of the annealed powders monotonically decreased as the annealing temperature increased. On the other hand, the coercivity of the annealed powders rapidly increased with increasing annealing temperature. The powders annealed at 600 °C had a saturation magnetization of 100 emu/g with a coercivity of 500 Oe. © 2000 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
82.30.-b Specific chemical reactions; reaction mechanisms
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Gh Other heat and thermomechanical treatments
81.40.Rs Electrical and magnetic properties related to treatment conditions

Magnetostrictive properties of a new type of Tb–Dy–Fe–Zn Laves phase compound

Hideaki Ono, Munekatsu Shimada, and Hideo Toma

J. Appl. Phys. 88, 7213 (2000); http://dx.doi.org/10.1063/1.1325003 (4 pages) | Cited 1 time

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The magnetostriction of (Tb–Dy)Fe2 Laves phase compounds, which are generally used under compressive prestress, is strongly dependent on prestress in an application range of 0–40 MPa. Magnetostriction shows an especially pronounced decline with increasing prestress in a range of 20–40 MPa. On the other hand, this tendency for magnetostriction to decrease with increasing prestress is suppressed in Tb–Dy–Fe–Zn Laves phase compounds in which Fe has been partially substituted by Zn. Under an applied magnetic field of 80 kA/m, which is the practical operating condition of actuators, magnetorestriction displays a tendency to increase under prestress of 40 MPa compared with that of nonsubstitution compounds. Additionally, the basic properties of this newly found type of Tb–Dy–Fe–Zn Laves phase magnetostrictive compound have also been identified. © 2000 American Institute of Physics.
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75.80.+q Magnetomechanical effects, magnetostriction
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
81.30.Fb Solidification

On the gradual character of the first-order spin reorientation transition in DyFe11Ti

M. D. Kuz’min

J. Appl. Phys. 88, 7217 (2000); http://dx.doi.org/10.1063/1.1327605 (6 pages) | Cited 9 times

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Proceeding from recently published crystal field parameters, I demonstrate that the first-order spin reorientation transition point in DyFe12−xTix depends strongly on the value of titanium content x. This leads, due to inevitable small spatial variation of composition, to significant broadening of the first-order transition, giving it an appearance of a continuous process. Yet it can be unmistakably identified as a first-order phase transition, thanks to the characteristic shape of the temperature dependence of the spin orientation angle θ. What makes first- and second-order spin reorientation transitions clearly distinct is the shape, rather than width, of the “step” in the θ(T) dependence. Small differences of composition are also found to account for the outstanding discrepancies between the experimental studies carried out on different single crystals of DyFe11Ti, thus bringing the decade-long controversy to an end. © 2000 American Institute of Physics.
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75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
71.70.Ch Crystal and ligand fields

Photoexcited spin-glass state in (Mg, Fe){Mg,Fe,Ti}O4 spinel ferrite films

Yuji Muraoka, Hitoshi Tabata, and Tomoji Kawai

J. Appl. Phys. 88, 7223 (2000); http://dx.doi.org/10.1063/1.1327601 (7 pages) | Cited 6 times

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Spin-glass states above room temperature have been found in (Mg, Fe){Mg,Fe,Ti}2O4 spinel ferrite thin films formed on Al2O3 (0001) and SrTiO3 (111) substrates. The films show a long-time relaxation of the magnetization in zero-field-cooled operation and a frequency dependence of the cusp temperature in ac susceptibility measurement, both of which are typical characteristics of a spin glass. This high-temperature spin-glass state has been achieved by the fine tuning of spin states through the control of composition, random oxygen deficiencies, and the stress induced by the film/substrate lattice mismatch, all of which give rise to effects that enhance the exchange interaction of spins in the ferrite films. We have demonstrated the change of magnetic state by means of light irradiation from spin glass to a ferrimagnet over a wide range of temperatures below 290 K. The direct photoexcitation of spins with photon energy in the visible-light region (1.7–3.2 eV), which corresponds to the spin excitation energy of crystal field for Fe ions located in both tetrahedral and octahedral sites, is effective for realizing photoinduced magnetization. © 2000 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Gg Ferrimagnetics
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Lk Spin glasses and other random magnets
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Et Exchange and superexchange interactions

The properties and magnetically softened grain boundaries of Nd10Fe84−xB6Inx (x=0,1,2) exchange coupling magnets

Q. G. Ji, B. X. Gu, and Y. W. Du

J. Appl. Phys. 88, 7230 (2000); http://dx.doi.org/10.1063/1.1323530 (4 pages) | Cited 1 time

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The magnetic behavior of Nd10Fe84−xB6Inx (x=0,1,2) nanocomposites was investigated. It was found that a certain amount of indium (x=1) added to Nd10Fe84B6 magnets enhances the hard magnetic properties. The optimum coercivity and remanence ratio was increased from 5.0 kOe and 0.71 to 5.8 kOe and 0.83, respectively. The squareness of the hysteresis loop is improved greatly. The maximum magnetic energy product (BH)max increases remarkably from 12 to 18 MGOe. The origin for those enhancements is mainly attributed to the magnetically softened grain boundaries and enhanced crystallographical coherency by indium addition. The magnetic annealing is found to be helpful to enhance the coherency and coupling between hard and soft phases. © 2000 American Institute of Physics.
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75.50.Ww Permanent magnets
61.72.Mm Grain and twin boundaries
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.30.Et Exchange and superexchange interactions
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
75.60.Nt Magnetic annealing and temperature-hysteresis effects

Magnetic and structural properties of hexagonal-close-packed-CoCrPt–C granular media for high areal density recording

Yingfan Xu, Jian Ping Wang, Z. S. Shan, Hua Jiang, and Chong Tow Chong

J. Appl. Phys. 88, 7234 (2000); http://dx.doi.org/10.1063/1.1329147 (8 pages) | Cited 5 times

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Magnetic and structural properties of hexagonal-close-packed-(CoCrPt)100−xCx thin films for potential applications in magnetic recording media have been investigated. CrTi and Cr underlayers were used to improve the in-plane preferred orientation. High coercivity of 4.4 kOe and anisotropy of 3.6×106 erg/cm3 have been achieved in films with a CrTi underlayer after postdeposition annealing. The addition of Ti to the Cr underlayer results in lower annealing temperature and shorter annealing time, while retaining higher coercivity. Vibrating sample magnetometer measurements showed that the magnetic moment lies fairly well in the film plane under proper preparation conditions; while x-ray diffraction measurements showed that the CrTi underlayer promoted Co (10.0) in-plane preferred orientation. Grain isolation in the magnetic layer was improved by the segregated C and further enhanced by postdeposition annealing. The peak value of δM curves decreased upon annealing and changed to a negative value when higher annealing temperatures were applied, indicating that strong exchange coupling in as-deposited film decreased and changed to dipolar interaction dominance upon annealing. © 2000 American Institute of Physics.
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75.50.Ss Magnetic recording materials
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Cr Saturation moments and magnetic susceptibilities
61.72.Cc Kinetics of defect formation and annealing
75.50.Vv High coercivity materials
75.30.Gw Magnetic anisotropy
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Effects of postannealing on the electrical properties of Ta2O5 thin films deposited on TiN/T

Chich-Shang Chang, Tzu-Ping Liu, and Tai-Bor Wu

J. Appl. Phys. 88, 7242 (2000); http://dx.doi.org/10.1063/1.1326464 (7 pages) | Cited 7 times

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The effects of postannealing on the structural and leakage current characteristics of Ta2O5 thin films deposited on a TiN/Ti bottom electrode by chemical-vapor deposition at 350 °C were investigated. The Ta2O5 film of 50 nm thickness shows an amorphous phase and smooth surface morphology after annealing in N2O plasma at 350 °C, but the film treated with rapid thermal annealing in nitrogen (RTN) at 750 °C prior to N2O plasma annealing at 350 °C has an orthorhombic structure and rugged surface morphology. In addition, the TiSi phase also appears in the specimen of RTN-treated Ta2O5 film. Moreover, the residual carbon can be effectively eliminated and the oxygen deficiency can be well compensated by the N2O plasma annealing for both amorphous and crystalline Ta2O5 films. The I–V relation of the amorphous Ta2O5 films is asymmetric with respect to the biasing polarity, which indicates that the leakage current is primarily dominated by the Schottky emission. On the other hand, the crystalline Ta2O5 film has a symmetrical I–V relation, suggesting that the non-Ohmic leakage in the crystalline Ta2O5 film is related to the Poole–Frenkel effect. The barrier heights φB for the non-Ohmic leakage in the amorphous and crystalline Ta2O5 films, as evaluated from the temperature dependence of the I–V relation, are 0.52 and 0.82 eV, respectively. © 2000 American Institute of Physics.
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61.72.Cc Kinetics of defect formation and annealing
73.61.Ng Insulators
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.50.Fq High-field and nonlinear effects

Effect of composition and temperature on field-induced properties in the lead strontium zirconate titanate system

Yongjian Yu and Raj N. Singh

J. Appl. Phys. 88, 7249 (2000); http://dx.doi.org/10.1063/1.1325380 (9 pages) | Cited 16 times

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The electric field-induced antiferroelectric (AFE) to ferroelectric (FE) phase transition in lead strontium zirconate titanate (PSZT) ceramics was studied by means of dielectric, polarization, and strain hysteresis measurements. PSZT compositions with varying strontium and Zr/Ti ratio, located in the ferroelectric, antiferroelectric phase regions, and near the AFE/FE phase boundary were prepared. Dielectric properties were measured as a function of temperature for different compositions. The electric field required for AFE–FE phase transition and hysteresis were affected by the temperature and composition. The entropy change during phase transition and the field-induced strain were also measured and discussed. © 2000 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
77.80.Dj Domain structure; hysteresis
77.80.B- Phase transitions and Curie point

Microstructure, structural defects, and piezoelectric response of Bi4Ti3O12 modified by Bi3TiNbO9

Laurent Sagalowicz, Fan Chu, Pedro Duran Martin, and Dragan Damjanovic

J. Appl. Phys. 88, 7258 (2000); http://dx.doi.org/10.1063/1.1327285 (6 pages) | Cited 18 times

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Microstructure, structural defects, and piezoelectric response of bismuth titanate (Bi4Ti3O12)1−x and bismuth titanium niobate (Bi3TiNbO9)x solid solution with x=0.05 and 0.2 were investigated. Depending on x and on the sintering temperature different microstructures and piezoelectric responses were observed. For a low content in Bi3TiNbO9 (x=0.05) and a high sintering temperature (1130 °C), a coarse grain size is present, the number of structural defects within the grain is small, and there is a strong dependence of d33 on the ac pressure. For higher Bi3TiNbO9 (x=0.2) content or for lower sintering temperature (1080 °C) and x=0.05, the grain size is finer and a large number of structural defects is present within the grains. In particular, for x=0.2, high resolution transmission electron microscopy shows a high concentration of intergrowth defects which consist of Bi3TiNbO9 layers inserted in the Bi4Ti3O12 matrix in a more or less random way. In these samples, there is a very small dependence of d33 on the ac pressure and the piezoelectric hysteresis is likewise very small. The relation between microstructure and piezoelectric properties is discussed and it is shown that there is a good correlation between the dependence of the piezoelectric response on the ac pressure and the defect density. The piezoelectric response may be related to the structural defects present within the grain. © 2000 American Institute of Physics.
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77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.65.Bn Piezoelectric and electrostrictive constants
61.72.-y Defects and impurities in crystals; microstructure

Equivalent pyroelectric coefficient of a pyroelectric bimorph structure

L. Pintilie, I. Pintilie, and I. Matei

J. Appl. Phys. 88, 7264 (2000); http://dx.doi.org/10.1063/1.1327284 (8 pages) | Cited 5 times

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A detailed formula for the equivalent pyroelectric coefficient of a bimorph structure acting as a pyroelectric detector was deduced. It is shown that electric fields occur in the structure when it is subjected to a temperature variation, due to the unequal charges generated by the two components. The field dependence of the ferroelectric polarization has to be considered in this case and the (∂P/∂E) derivative appears explicitly in the deduced formula. The effect is that the equivalent pyroelectric coefficient has different values for heating and cooling. This could lead to a redressing effect on the pyroelectric signal if the temperature difference varies periodically. The equivalent pyroelectric coefficient is, also, thickness dependent. This fact offers the possibility of designing structures with high values of pyroelectric coefficient compared with the values of the component phases. © 2000 American Institute of Physics.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
07.20.-n Thermal instruments and apparatus
77.80.-e Ferroelectricity and antiferroelectricity
77.22.Ej Polarization and depolarization

Fatigue anisotropy in single crystal Pb(Zn1/3Nb2/3)O3–PbTiO3

Koichi Takemura, Metin Ozgul, Veronique Bornand, Susan Trolier-McKinstry, and Clive A. Randall

J. Appl. Phys. 88, 7272 (2000); http://dx.doi.org/10.1063/1.1314325 (6 pages) | Cited 33 times

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Fatigue rates in the Pb(Zn1/3Nb2/3)O3–PbTiO3 perovskite solid solution were investigated for different compositions in the rhombohedral and tetragonal phases in a variety of directions, at various field levels. It was found that the fatigue rates depend on both the ferroelectric phase and crystallographic orientation. In the rhombohedral phase when the field is applied along the [001]C direction (where the direction is given in terms of the cubic prototype), excellent fatigue resistance was obtained. © 2000 American Institute of Physics.
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77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization
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