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22 Jul 2002

Volume 81, Issue 4, pp. 571-782

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Sensitive imaging of an elastic nonlinear wave-scattering source in a solid

Vyacheslav V. Kazakov, Alexander Sutin, and Paul A. Johnson

Appl. Phys. Lett. 81, 646 (2002); http://dx.doi.org/10.1063/1.1495081 (3 pages) | Cited 29 times

Online Publication Date: 16 July 2002

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We have developed an imaging method for locating isolated nonlinear scattering source(s) in solids. It relies on extracting the nonlinear response of a solid by modulation of a high by a low-frequency wave, and employing moving-window, synchronous detection. The resulting image consists of nonlinear wave reflection profiles with remarkable sensitivity to an isolated elastic nonlinear source(s). In creating the image, we can distinguish between a nonlinear scattering source and other wave scatterers in the material. The method should work equally well for imaging the relative nonlinearity of different regions within a volume. © 2002 American Institute of Physics.
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46.40.Cd Mechanical wave propagation (including diffraction, scattering, and dispersion)
43.25.Dc Nonlinear acoustics of solids

Interband optical properties of higher manganese silicide thin films

M. Rebien, W. Henrion, H. Angermann, and S. Teichert

Appl. Phys. Lett. 81, 649 (2002); http://dx.doi.org/10.1063/1.1496135 (3 pages) | Cited 8 times

Online Publication Date: 16 July 2002

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Semiconducting MnSi1.7 has been investigated by ellipsometric as well as reflectance and transmittance measurements. The interband dielectric functions of epitaxial films on Si(001) and polycrystalline films have been determined. Below the lowest direct transition at 0.96 eV, an indirect gap of 0.40 eV is obtained. The optical properties of the native oxide of MnSi1.7 are found to closely resemble those of SiO2. © 2002 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)
78.66.Li Other semiconductors
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Exciton spectra of an AlN epitaxial film on (0001) sapphire substrate grown by low-pressure metalorganic vapor phase epitaxy

T. Onuma, S. F. Chichibu, T. Sota, K. Asai, S. Sumiya, T. Shibata, and M. Tanaka

Appl. Phys. Lett. 81, 652 (2002); http://dx.doi.org/10.1063/1.1493666 (3 pages) | Cited 29 times

Online Publication Date: 16 July 2002

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Exciton resonance energies in an AlN epilayer on (0001) sapphire substrate grown by low-pressure metalorganic vapor phase epitaxy were determined as a function of temperature by means of optical reflectance (OR) and cathodoluminescence measurements. The OR spectra exhibited distinct reflectance anomalies at the photon energies just above the multiple internal reflection fringes, and the spectral line shape was fitted considering A (Γ7vu→Γ7c) and BC (Γ9v,Γ7vl→Γ7c) exciton transitions. The fitting gave the values of them at 0 K to be 6.211 and 6.266 eV, giving the crystal- field splitting (Δcr) of approximately 55 meV. The AlN film exhibited an excitonic emission even at 300 K, which is due to the small Bohr radius of excitons and large longitudinal optical phonon energies. The Einstein characteristic temperature ΘE was estimated to be 580 K. © 2002 American Institute of Physics.
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78.66.Fd III-V semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.60.Hk Cathodoluminescence, ionoluminescence
63.20.kk Phonon interactions with other quasiparticles
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.70.Ch Crystal and ligand fields

Local environment surrounding magnetic impurity atoms in a structural phase transition of Co-doped TiO2 nanocrystal ferromagnetic semiconductors

Y. L. Soo, G. Kioseoglou, S. Kim, Y. H. Kao, P. Sujatha Devi, John Parise, R. J. Gambino, and P. I. Gouma

Appl. Phys. Lett. 81, 655 (2002); http://dx.doi.org/10.1063/1.1495544 (3 pages) | Cited 45 times

Online Publication Date: 16 July 2002

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The local environment surrounding magnetic impurity atoms and the host crystal structure of codoped TiO2 (TiO2:Co) nanocrystal ferromagnetic semiconductors have been investigated using the x-ray absorption fine structure and powder diffraction techniques. It has been found that the magnetic Co impurity atoms substitute for the Ti sites in an anataselike local environment through a structural phase transition when the material changes from an amorphous phase to a mixture of anatase and rutile crystal structures and then to a rutile structure as a result of increasing the anneal temperature. This result reveals an interesting feature that the local structure around magnetic impurity atoms can remain practically unchanged while the material undergoes drastic structural variations and a loss of room-temperature ferromagnetism. © 2002 American Institute of Physics.
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64.70.Nd Structural transitions in nanoscale materials
61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
75.30.Hx Magnetic impurity interactions
75.50.Tt Fine-particle systems; nanocrystalline materials
61.72.S- Impurities in crystals
64.70.K- Solid-solid transitions
61.43.-j Disordered solids
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
78.70.Dm X-ray absorption spectra
75.30.Et Exchange and superexchange interactions
81.40.Gh Other heat and thermomechanical treatments
81.40.Rs Electrical and magnetic properties related to treatment conditions
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Pt Schottky contacts to n-(Ga,Mn)N

Jihyun Kim, F. Ren, G. T. Thaler, M. E. Overberg, C. R. Abernathy, S. J. Pearton, and R. G. Wilson

Appl. Phys. Lett. 81, 658 (2002); http://dx.doi.org/10.1063/1.1496130 (3 pages) | Cited 2 times

Online Publication Date: 16 July 2002

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The Schottky barrier height of Pt contacts on n-(Ga,Mn)N (n ∼ 3.5×1017 cm−3) thin films was obtained from current–voltage measurements as a function of temperature. The resulting values ranged from 0.82±0.04 eV at 25 °C to 0.79±0.06 eV at 100 °C with saturation current densities of 4.28×10−8 A cm−2 (25 °C) to 8.42×10−5 A cm−2 (100 °C), respectively. The barrier height at room temperature obtained from an activation energy plot was 0.91±0.06 eV. The reverse current magnitude was larger than predicted by thermionic emission alone, just as in n-GaN grown in a similar fashion on Al2O3 substrates. The measured barrier height for Pt on n-(Ga,Mn)N is lower than for the value reported on n-GaN(1.08 eV). © 2002 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
75.50.Pp Magnetic semiconductors

Tailoring the electronic properties of GaAs/AlAs superlattices by InAs layer insertions

A. Patanè, D. Sherwood, L. Eaves, T. M. Fromhold, M. Henini, P. C. Main, and G. Hill

Appl. Phys. Lett. 81, 661 (2002); http://dx.doi.org/10.1063/1.1496140 (3 pages) | Cited 14 times

Online Publication Date: 16 July 2002

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We investigate the electrical and optical properties of GaAs/AlAs superlattices (SLs) in which a thin (⩽1.2 monolayers) InAs layer is inserted in the central plane of each GaAs quantum well. The InAs layer modifies the structure of the SL unit cell and provides an additional design parameter for tailoring the energy of the lowest miniband and the size of the minigap. We exploit this effect to enhance electron injection from a doped contact layer into the first miniband and to inhibit interminiband coupling. © 2002 American Institute of Physics.
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73.21.Cd Superlattices
73.21.Fg Quantum wells
78.67.De Quantum wells
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
68.65.Cd Superlattices
68.65.Fg Quantum wells
81.07.St Quantum wells
68.35.Ct Interface structure and roughness
73.63.Hs Quantum wells

Initial growth of GaN on α-Al2O3(0001) by molecular beam epitaxy

S. K. Davidsson, T. G. Andersson, and H. Zirath

Appl. Phys. Lett. 81, 664 (2002); http://dx.doi.org/10.1063/1.1495083 (3 pages) | Cited 5 times

Online Publication Date: 16 July 2002

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The sapphire surface, used for growth of GaN by molecular beam epitaxy, was studied by reflection high-energy electron diffraction during the in situ pretreatment and initial growth. We investigated the effect of Ga cleaning, nitridation, and growth of the AlN nucleation layer on the lattice constant. One Ga-cleaning cycle restored the surface with a higher diffraction density. Nitridation changed the lattice constant instantaneously. The lattice constant was restored if the nitridation was switched off. For the AlN nucleation layer, the first monolayer was strained, followed by first a rapid and then a slow relaxation. © 2002 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
81.65.Cf Surface cleaning, etching, patterning

Accurate modeling of direct tunneling hole current in p-metal–oxide–semiconductor devices

A. Haque and K. Alam

Appl. Phys. Lett. 81, 667 (2002); http://dx.doi.org/10.1063/1.1495084 (3 pages) | Cited 10 times

Online Publication Date: 16 July 2002

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We critically examine a number of important issues related to modeling hole direct tunneling in p-metal–oxide–semiconductor devices with p+-polycrystalline silicon gate. By comparing our simulated direct tunneling hole current with experimental data, several observations are made. It is found that inelastic trap scattering of holes in the gate-oxide region increases the hole tunneling current significantly at lower gate voltages in devices with gate-oxide thickness greater than 2 nm. Appropriate spatial and gate bias dependence of the scattering rate needs to be considered for accurately predicting experimental current over the entire gate voltage range. Effective mass of holes in gate-oxide region is not a constant, rather, it increases with increasing gate bias voltage and we propose a relationship between the two. Bulk values for hole effective masses in silicon may be used to accurately model the hole tunneling current even in the presence of hole quantization. The contribution of split-off holes to direct tunneling current is not negligible in strong inversion. © 2002 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
73.20.At Surface states, band structure, electron density of states

Gain dynamics and ultrafast spectral hole burning in In(Ga)As self-organized quantum dots

K. Kim, J. Urayama, T. B. Norris, J. Singh, J. Phillips, and P. Bhattacharya

Appl. Phys. Lett. 81, 670 (2002); http://dx.doi.org/10.1063/1.1493665 (3 pages) | Cited 28 times

Online Publication Date: 16 July 2002

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Using a femtosecond three-pulse pump-probe technique, we investigated spectral hole-burning and gain recovery dynamics in self-organized In(Ga)As quantum dots. The spectral hole dynamics are qualitatively different from those observed in quantum wells, and allow us to distinguish unambiguously the gain recovery due to intradot relaxation and that due to carrier capture. The gain recovery due to carrier–carrier scattering-dominated intradot relaxation is very fast ( ∼ 130 fs), indicating that this is not the factor limiting the bandwidth of directly modulated quantum dot lasers. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
68.65.Hb Quantum dots (patterned in quantum wells)

Influence of exciton localization on the quantum efficiency of GaN/(In,Ga)N multiple quantum wells grown by molecular-beam epitaxy

S. Dhar, U. Jahn, O. Brandt, P. Waltereit, and K. H. Ploog

Appl. Phys. Lett. 81, 673 (2002); http://dx.doi.org/10.1063/1.1493237 (3 pages) | Cited 9 times

Online Publication Date: 16 July 2002

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Using cathodoluminescence spectroscopy, we investigate the dependence of the transition energy and quantum efficiency of a GaN/(In,Ga)N multiple quantum-well structure on both the temperature and excitation density. A coupled rate-equation model is introduced to explain the experimental results. Polarization field screening has been incorporated in a realistic manner by solving these coupled rate equations self-consistently along with the Schrödinger and Poisson equations. Our study suggests that exciton localization increases the internal quantum efficiency significantly. © 2002 American Institute of Physics.
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73.21.Fg Quantum wells
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.67.De Quantum wells
78.60.Hk Cathodoluminescence, ionoluminescence
73.20.Fz Weak or Anderson localization
71.35.Lk Collective effects (Bose effects, phase space filling, and excitonic phase transitions)

Electron energy-loss spectroscopy analysis of interface structure of yttrium oxide gate dielectrics on silicon

D. Niu, R. W. Ashcraft, Z. Chen, S. Stemmer, and G. N. Parsons

Appl. Phys. Lett. 81, 676 (2002); http://dx.doi.org/10.1063/1.1496138 (3 pages) | Cited 7 times

Online Publication Date: 16 July 2002

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Interface stability of high dielectric constant gate insulators on silicon is an important issue for advanced gate stack engineering. In this article, we analyze the silicon/dielectric interface structure for thin Y2O3 and Y silicate films deposited by chemical vapor deposition on clean and prenitrided Si(100) using high-resolution transmission electron microscopy, electron energy-loss spectroscopy, and x-ray photoelectron spectroscopy. The analysis shows the films to be stoichiometric Y2O3 on top and Y-silicate/SiO2 at the dielectric/Si interface. Prenitridation of the silicon surface impedes the reaction between the depositing film and the substrate, promoting a Si-free Y2O3 structure. Possible mechanisms leading to the observed Y2O3 and Y silicate structures are discussed. © 2002 American Institute of Physics.
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68.35.Ct Interface structure and roughness
81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.05.Cy Elemental semiconductors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
68.55.-a Thin film structure and morphology
79.20.Uv Electron energy loss spectroscopy
68.37.Lp Transmission electron microscopy (TEM)
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

Transient carrier velocities in bulk GaAs: Quantitative comparison between terahertz data and ensemble Monte Carlo calculations

M. Abe, S. Madhavi, Y. Shimada, Y. Otsuka, K. Hirakawa, and K. Tomizawa

Appl. Phys. Lett. 81, 679 (2002); http://dx.doi.org/10.1063/1.1495540 (3 pages) | Cited 14 times

Online Publication Date: 16 July 2002

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Transient carrier velocities determined from terahertz radiation emitted from photoexcited bulk GaAs have been compared with ensemble Monte Carlo calculations. It is found that, if actual experimental conditions (sample geometry, photoexcitation condition, etc.) are properly taken into account, Monte Carlo calculations give a very good description of the transient carrier velocities determined from THz measurements. Although the THz signal is dominated by electron transport, contribution of holes becomes appreciable when the electric field is higher than 20 kV/cm. © 2002 American Institute of Physics.
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72.20.Ht High-field and nonlinear effects
72.80.Ey III-V and II-VI semiconductors
81.05.Ea III-V semiconductors
72.40.+w Photoconduction and photovoltaic effects
78.55.Cr III-V semiconductors
72.20.Dp General theory, scattering mechanisms
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Switch using d-wave symmetry of YBa2Cu3O7−δ Josephson junction

Youichi Enomoto, Tomohiro Nishihara, Hiroaki Myouren, and Susumu Takada

Appl. Phys. Lett. 81, 682 (2002); http://dx.doi.org/10.1063/1.1494108 (3 pages)

Online Publication Date: 16 July 2002

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Switching functions using a parallel connection of conventional-type and π-type junctions have been investigated. Both junctions consist of Nb/Au/YBa2Cu3O7−δ Josephson junctions on YBa2Cu3O7−δ edges, whose faces are (110) and (100). The modulation patterns of critical currents in low magnetic fields indicate that the d-wave component is dominant: the (100) junctions exhibit the conventional type, but the (110) junctions the π type. Superconducting current path is alternated between the conventional junction and the π junction by applied magnetic fields using these anisotropic magnetic field dependences of the critical current. © 2002 American Institute of Physics.
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74.50.+r Tunneling phenomena; Josephson effects
85.25.Cp Josephson devices
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.72.-h Cuprate superconductors
74.25.Sv Critical currents

Interfacial structure of epitaxial MgB2 thin films grown on (0001) sapphire

W. Tian, X. Q. Pan, S. D. Bu, D. M. Kim, J. H. Choi, S. Patnaik, and C. B. Eom

Appl. Phys. Lett. 81, 685 (2002); http://dx.doi.org/10.1063/1.1489101 (3 pages) | Cited 15 times

Online Publication Date: 16 July 2002

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The microstructure and interfacial atomic structure of MgB2 thin films fabricated on the (0001) Al2O3 substrate were characterized by transmission electron microscopy. It was found that the MgB2 films grow epitaxially on the substrate with an orientation relationship with respect to the substrate as: (0001)MgB2∥(0001)Al2O3 and [11math0]MgB2∥[10math0]Al2O3. At the film/substrate interface, both MgO and MgAl2O4 phases were observed, which also grow epitaxially on the (0001) Al2O3 substrate. The formation of these intermediate phases is ascribed to the existence of oxygen during the annealing. © 2002 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
68.35.Ct Interface structure and roughness
68.37.Lp Transmission electron microscopy (TEM)
68.55.A- Nucleation and growth

Transmission electron microscopy evidence for phase transformation from Bi2Sr2CuO6 to Bi2Sr2Ca2Cu3O10

W. M. Chen, G. Li, S. S. Jiang, H. Y. Ling, P. Yao, M. J. Qin, H. K. Liu, and S. X. Dou

Appl. Phys. Lett. 81, 688 (2002); http://dx.doi.org/10.1063/1.1492856 (3 pages) | Cited 4 times

Online Publication Date: 16 July 2002

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The growth mechanism of the Bi-2223 phase was studied using multifilamentary Ag/Bi-2223 tapes manufactured by the powder-in-tube method. X-ray powder diffraction was performed to analyze the developments of Bi-2201, Bi-2212, and Bi-2223 phases during sintering periods at high temperatures. Transmission electron microscopy (TEM) was used to investigate the growth mechanism of the 2223 phase. TEM images indicated that 2201 and Ca2CuO3 crystals come together to form platelets of 2223. The structural phase transformation established a structural frame of the 2223 crystal. There were some vacant defects retaining in the established 2223 crystal cells at copper and oxygen sites after the phase transformation, and the Cu/O compound at high temperatures would diffuse into 2223 cells and occupy the corresponding vacancies to complete the 2223 crystal structure. The present work provides an evidence for growing the 2223 phase from the 2201 phase and Ca2CuO3 in the samples studied. © 2002 American Institute of Physics.
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74.72.-h Cuprate superconductors
84.71.Mn Superconducting wires, fibers, and tapes
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
64.70.K- Solid-solid transitions
64.75.-g Phase equilibria
66.30.J- Diffusion of impurities
61.72.J- Point defects and defect clusters

Strong wave-vector filtering and nearly 100% spin polarization through resonant tunneling antisymmetrical magnetic structure

H. Z. Xu and Z. Shi

Appl. Phys. Lett. 81, 691 (2002); http://dx.doi.org/10.1063/1.1495541 (3 pages) | Cited 31 times

Online Publication Date: 16 July 2002

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Strong spin- and wave-vector dependent upon electron resonant tunneling through antisymmetrical double-barrier magnetic structures are revealed. The electron transmission probability and the polarization of transmitted beams as a function of incident electron energy for different structures have been calculated. It is shown that the antisymmetric magnetic structure possesses the strongest spin polarization and well-pronounced wave-vector filtering properties. Surprisingly, a polarization of nearly 100% can be achieved by spin-dependent resonant tunneling in these structures, although the average magnetic field of the structures is zero. © 2002 American Institute of Physics.
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72.25.Mk Spin transport through interfaces
73.23.Hk Coulomb blockade; single-electron tunneling
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.40.Gk Tunneling
85.75.Mm Spin polarized resonant tunnel junctions
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Spin-polarized light-emitting diode using metal/insulator/semiconductor structures

T. Manago and H. Akinaga

Appl. Phys. Lett. 81, 694 (2002); http://dx.doi.org/10.1063/1.1496493 (3 pages) | Cited 51 times

Online Publication Date: 16 July 2002

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We have succeeded in growing ferromagnetic metals (Co,Fe,andNiFe)/Al2O3/AlGaAs heterostructures with homogeneous flat interfaces. The electroluminescence from a light-emitting diode with a metal/insulator/semiconductor (MIS) structure depends on the magnetization direction of the ferromagnetic electrode. This fact shows that a spin injection from the ferromagnetic metal to the semiconductor is achieved. The spin-injection efficiency is estimated to be the order of 1% at room temperature. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
72.25.Hg Electrical injection of spin polarized carriers
72.25.Mk Spin transport through interfaces
78.60.Fi Electroluminescence
81.05.Ea III-V semiconductors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.30.Tv Field effect devices
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Mechanism of low temperature hydrogen-annealing-induced degradation in Pb(Zr0.4Ti0.6)O3 capacitors

Sunae Seo, Jong-Gul Yoon, T. K. Song, B. S. Kang, T. W. Noh, Y. K. Lee, Ch. J. Kim, and Y. S. Park

Appl. Phys. Lett. 81, 697 (2002); http://dx.doi.org/10.1063/1.1492006 (3 pages) | Cited 11 times

Online Publication Date: 16 July 2002

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Changes in the polarization–field hysteresis loop were systematically investigated for Pb(Zr0.4Ti0.6)O3 capacitors after forming gas annealing at 200 °C. Voltage shift in hysteresis was strongly dependent on the polarization states and ascribed to an asymmetric distribution of defect charges and pinned defect dipoles. Field recovery of the imprinted capacitors and increase in coercive field after the recovery were discussed in conjunction with reversible defect dipoles. From the relaxation of the voltage shift with an activation energy of 0.21 eV, it is inferred that charge trapping may be the main cause of the voltage shift and the subsequent degradation of the capacitors by pinning the polarization and defect dipoles. © 2002 American Institute of Physics.
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84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
61.72.Cc Kinetics of defect formation and annealing
77.80.Dj Domain structure; hysteresis

Effect of Li diffusion on the domain inversion of LiNbO3 prepared by vapor transport equilibration

Yunlin Chen, Jingjun Xu, Yongfa Kong, Shaolin Chen, Guangyin Zhang, and Jianping Wen

Appl. Phys. Lett. 81, 700 (2002); http://dx.doi.org/10.1063/1.1494852 (3 pages) | Cited 4 times

Online Publication Date: 16 July 2002

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LiNbO3 crystals with a composition close to stoichiometry were prepared by using a vapor transport equilibration (VTE) technique. The influence of the intrinsic defect density in the electric field periodic poling LiNbO3 crystal is studied. The switching field is found to decrease with the intrinsic defects. The reduction of intrinsic defects is mainly due to a change in the Li/Nb ratio in the LiNbO3 crystal, as a result of lithium diffusion during the VTE process. The switching field of ∼ 2 kV/mm in stoichiometric LiNbO3 is about one fourth of the previously published results obtained with near-stoichiometric crystals, and is approximately one tenth of the conventional congruent field. Periodic poling of thicker stoichiometric substrates was successfully performed by means of an electric field poling process at room temperature. © 2002 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization
66.30.H- Self-diffusion and ionic conduction in nonmetals
77.80.Fm Switching phenomena
61.72.J- Point defects and defect clusters

Exploring grain size as a cause for “dead-layer” effects in thin film capacitors

L. J. Sinnamon, M. M. Saad, R. M. Bowman, and J. M. Gregg

Appl. Phys. Lett. 81, 703 (2002); http://dx.doi.org/10.1063/1.1494837 (3 pages) | Cited 55 times

Online Publication Date: 16 July 2002

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Pulsed laser deposition was used to make a series of Au/Ba0.5Sr0.5TiO3 (BST)/SrRuO3/MgO thin film capacitors with dielectric thickness ranging from ∼15 nm to ∼1 μm. Surface grain size of the dielectric was monitored as a function of thickness using both atomic force microscopy and transmission electron microscopy. Grain size data were considered in conjunction with low field dielectric constant measurements. It was observed that the grain size decreased with decreasing thickness in a manner similar to the dielectric constant. Simple models were developed in which a functionally inferior layer at the grain boundary was considered as responsible for the observed dielectric behavior. If a purely columnar microstructure was assumed, then constant thickness grain-boundary dead layers could indeed reproduce the series capacitor dielectric response observed, even though such layers would contribute electrically in parallel with unaffected bulk-like BST. Best fits indicated that the dead layers would have a relative dielectric constant ∼40, and thickness of the order of tens of nanometers. For microstructures that were not purely columnar, models did not reproduce the observed dielectric behavior well. However, cross-sectional transmission electron microscopy indicated columnar microstructure, suggesting that grain boundary dead layers should be considered seriously in the overall dead-layer debate. © 2002 American Institute of Physics.
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84.32.Tt Capacitors
81.15.Fg Pulsed laser ablation deposition

Random exchange-type electro-optic behavior of Pb0.865La0.09(Zr0.65Ti0.35)O3 relaxor ferroelectrics

Dal-Young Kim, Jong-Jin Choi, and Hyoun-Ee Kim

Appl. Phys. Lett. 81, 706 (2002); http://dx.doi.org/10.1063/1.1496132 (3 pages) | Cited 5 times

Online Publication Date: 16 July 2002

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Random exchange nature of Pb0.865La0.09(Zr0.65Ti0.35)O3 relaxor ferroelectrics was revealed by electro-optic study. Time decay behavior of birefringence was measured after switching off the external bias field, and showed random exchange-type behavior. Specific heat behavior was also obtained from the temperature derivatives of birefringence, and its critical exponent was α = −0.09 as predicted by the random exchange Ising model. We think the random exchange interaction is induced by nonpolar La ions and vacancies. © 2002 American Institute of Physics.
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78.20.Jq Electro-optical effects
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
77.80.-e Ferroelectricity and antiferroelectricity
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
71.70.Gm Exchange interactions
77.22.Ej Polarization and depolarization
65.40.Ba Heat capacity
78.20.Fm Birefringence

Model for interface defect and positive charge generation in ultrathin SiO2/ZrO2 gate dielectric stacks

M. Houssa, J. L. Autran, A. Stesmans, and M. M. Heyns

Appl. Phys. Lett. 81, 709 (2002); http://dx.doi.org/10.1063/1.1496146 (3 pages) | Cited 26 times

Online Publication Date: 16 July 2002

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The generation of interface defects and positive charge during the injection of electrons in p-Si/SiO2/ZrO2/TiN structures is investigated. The kinetics of generation of both type of defects are found to be very similar. A model is proposed to explain the interface defect generation, based on the depassivation of trivalent silicon dangling bonds (Si3�SiH→Si3�Si⋅) at the (100)Si/SiO2 interface by the injected electrons. A Gaussian spread for the activation energy Ed related to the dissociation of the Si–H bond is included in this model. Comparison with experimental results reveals that the mean value of the activation energy Edi decreases linearly with the electric field Eox across the SiO2 layer. This behavior is attributed to the alignment of the Si–H dipole moment with respect to Eox, which favors dissociation of the Si–H bond. The hint of a correlation between the interface defect and positive charge generation suggests that the positively charged centers might be hydrogen-induced overcoordinated oxygen centers. © 2002 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Reactions of Y2O3 films with (001) Si substrates and with polycrystalline Si capping layers

Susanne Stemmer, Dmitri O. Klenov, Zhiqiang Chen, Dong Niu, Robert W. Ashcraft, and Gregory N. Parsons

Appl. Phys. Lett. 81, 712 (2002); http://dx.doi.org/10.1063/1.1496500 (3 pages) | Cited 12 times

Online Publication Date: 16 July 2002

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We use electron energy-loss spectroscopy in scanning transmission electron microscopy to investigate interfacial reactions of chemical vapor deposited Y2O3 films with the Si substrate and with in situ polycrystalline Si (“poly-Si”) capping layers after postdeposition annealing. We find that in situ capping layers significantly reduce the formation of SiO2 at the interface with the substrate, but silicates form at the substrate and the capping layer interfaces. Predeposition nitridation of the Si surface can impede the reaction at the substrate interface, resulting in crystallization of Y2O3 in the film interior. Possible mechanisms of the silicate formation are discussed. © 2002 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
79.20.Uv Electron energy loss spectroscopy
68.37.Lp Transmission electron microscopy (TEM)
61.72.Cc Kinetics of defect formation and annealing

Study of domain stability on (Pb0.76Ca0.24)TiO3 thin films using piezoresponse microscopy

H. Y. Guo, J. B. Xu, I. H. Wilson, Z. Xie, E. Z. Luo, Seungbum Hong, and H. Yan

Appl. Phys. Lett. 81, 715 (2002); http://dx.doi.org/10.1063/1.1494122 (3 pages) | Cited 21 times

Online Publication Date: 16 July 2002

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We introduce a method to investigate the domain stability issue based on piezoresponse microscopy. The switching and back-switching processes of sol–gel derived (Pb0.76Ca0.24)TiO3 thin films were investigated by comparing the local piezoelectric hysteresis loops in continuous mode and pulse mode. It was found that the local hysteresis loops acquired by the pulse mode in shorter pulse width were dominated by the back-switching process while the continuous mode piezoelectric hysteresis loop provides information on the domain switching process. © 2002 American Institute of Physics.
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77.80.Dj Domain structure; hysteresis
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Fm Switching phenomena
77.55.-g Dielectric thin films
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
77.65.-j Piezoelectricity and electromechanical effects

Microwave frequency tuning and harmonic generation in ferroelectric thin film transmission lines

James C. Booth, R. H. Ono, Ichiro Takeuchi, and Kao-Shuo Chang

Appl. Phys. Lett. 81, 718 (2002); http://dx.doi.org/10.1063/1.1494854 (3 pages) | Cited 10 times

Online Publication Date: 16 July 2002

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We evaluate dielectric tuning on nanosecond time scales in ferroelectric Ba0.3Sr0.7TiO3 thin films by measuring nonlinear harmonic generation at a fundamental frequency of 3 GHz. We compare the form of the distributed nonlinear capacitance per unit length C(Vrf) extracted from a simple model of harmonic generation in coplanar waveguide transmission line structures with the nonlinear capacitance C(Vdc) measured using a dc bias voltage, and obtain excellent agreement for temperatures in the range 235–295 K. This demonstrated agreement implies that full dielectric tuning can be expected in these ferroelectric thin films on nanosecond time scales, and also demonstrates that detrimental high-frequency nonlinear effects in device structures can be accurately predicted based on dc biased measurements. © 2002 American Institute of Physics.
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84.40.Az Waveguides, transmission lines, striplines
77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
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