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23 Apr 2001

Volume 78, Issue 17, pp. 2417-2603

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Cooperative nucleation and evolution in InGaAs quantum dots in multiply stacked structures

Qianghua Xie, J. L. Brown, and J. E. Van Nostrand

Appl. Phys. Lett. 78, 2491 (2001); http://dx.doi.org/10.1063/1.1365102 (3 pages) | Cited 6 times

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We report a type of vertical self-organization of In0.6Ga0.4As quantum dots (QDs) wherein the dot density for the top layer (NT) doubles that of the seed layer (NS). The experimental observation fits well with a scheme of QD vertical self-organization accompanied by additional cooperative dot nucleation at the face centers of an approximate two-dimensional array defined by the embedded seed dots. The dots in the top layer undergo a shape transition from {023} to {011} and a simultaneous shape stabilization and size equalization. © 2001 American Institute of Physics.
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81.05.Ea III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots

Spinodal decomposition in the BxGayIn1−x−yAs alloys

R. Asomoza, V. A. Elyukhin, and R. Peña-Sierra

Appl. Phys. Lett. 78, 2494 (2001); http://dx.doi.org/10.1063/1.1368193 (3 pages) | Cited 3 times

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Spinodal decomposition of the BxGayIn1−x−yAs quaternary alloys lattice-matched to the GaAs as the result of the internal deformation and coherency strain energies is described. The alloys are represented in the strictly regular approximation. The internal deformation energy is considered by the valence-force field model. The estimated bond-stretching and bond-bending elastic constants of BAs are αBAs = 6.69×10−2 N/m and βBAs = 1.81×10−2 N/m, respectively. Ranges of spinodal decomposition of the BxGayIn1−x−yAs quaternary alloys up to x ⩽ 0.1 with and without coherency strain energy are demonstrated. © 2001 American Institute of Physics.
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81.05.Ea III-V semiconductors
64.75.-g Phase equilibria
62.20.D- Elasticity
61.50.Lt Crystal binding; cohesive energy

Investigation of inversion domains in GaN by electric-force microscopy

K. M. Jones, P. Visconti, F. Yun, A. A. Baski, and H. Morkoç

Appl. Phys. Lett. 78, 2497 (2001); http://dx.doi.org/10.1063/1.1358359 (3 pages) | Cited 29 times

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Inversion domains in III-nitride semiconductors degrade the performance of devices fabricated in them. Consequently, it is imperative that we understand their electrostatic manifestation, the growth conditions under which such domains form, and an effective means of their identification. In what is nominally referred to as Ga-polarity samples, N-polarity domains have a polarization that is reversed with respect to the remainder of the surface, and therefore, have a different potential under strain. We have used surface-potential electric-force microscopy (SP-EFM) to image the electrostatic surface potential of GaN grown on sapphire, which is strained due to the thermal mismatch between the substrate and GaN. Employing a control sample with side-by-side Ga- and N-polarity regions, we have established the EFM mode necessary to identify inversion domains on GaN samples grown by molecular-beam epitaxy. This method is not sensitive to topology and has a spatial resolution of under 100 nm. The measured surface potentials for Ga-face and N-face regions are +25±10 and −30±10 mV, respectively, with respect to the sapphire substrate, where the sign is consistent with Ga- and N-polarity GaN under compressive strain due to thermal mismatch with the sapphire substrate. © 2001 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.40.Cg Contact resistance, contact potential
68.37.Ps Atomic force microscopy (AFM)
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What determines the emission peak energy of the blue luminescence in highly Mg-doped p-GaN?

J. S. Colton and P. Y. Yu

Appl. Phys. Lett. 78, 2500 (2001); http://dx.doi.org/10.1063/1.1367904 (3 pages) | Cited 8 times

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We report a study of the 2.8 eV blue luminescence (BL) in heavily Mg-doped p-GaN via resonant excitation with a tunable blue dye laser. The dependence of the BL on the excitation photon energy (Eex) is unlike that of the yellow luminescence found in n-type GaN. An Urbach-type band tail, with Urbach parameter of 33 meV is observed in the vicinity of the BL energy. We propose that the peak energy of the BL marks the transition from localized states to delocalized states within this band tail. © 2001 American Institute of Physics.
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71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors
71.20.Nr Semiconductor compounds

Electron affinity of AlxGa1−xN(0001) surfaces

S. P. Grabowski, M. Schneider, H. Nienhaus, W. Mönch, R. Dimitrov, O. Ambacher, and M. Stutzmann

Appl. Phys. Lett. 78, 2503 (2001); http://dx.doi.org/10.1063/1.1367275 (3 pages) | Cited 46 times

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The electronic properties and the electron affinities of AlxGa1−xN(0001) surfaces were investigated by ultraviolet photoemission spectroscopy (UPS) over the whole composition range. The samples were prepared by N-ion sputtering and annealing. Surface cleanliness and stoichiometry were monitored with x-ray photoemission spectroscopy. Samples with high aluminum content showed traces of oxygen which could not be removed by further cleaning cycles. However, we have evidence that the oxygen is located in the bulk and not at the surface. From the UP spectra the ionization energies and electron affinities as a function of composition x were determined. A decrease in electron affinity with increasing aluminum content was found, but the electron affinity remains positive for all x. Thus, earlier predictions of negative electron affinity for high aluminum content were not confirmed. © 2001 American Institute of Physics.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
81.05.Ea III-V semiconductors
68.35.Dv Composition, segregation; defects and impurities
79.60.Bm Clean metal, semiconductor, and insulator surfaces
81.40.Gh Other heat and thermomechanical treatments
81.65.Cf Surface cleaning, etching, patterning

Metastability of defects in p-GaAs grown from a Ga-rich melt

Z.-Q. Fang, J. W. Kim, and P. W. Yu

Appl. Phys. Lett. 78, 2506 (2001); http://dx.doi.org/10.1063/1.1365100 (3 pages) | Cited 1 time

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We report the observation of metastability for defects in Si-doped p-GaAs grown from a Ga-rich melt. A configuration change occurs suddenly at a critical temperature (near 120 K) during cooldown scans, giving rise to discontinuous deep-level transient spectra. A similar phenomenon was observed on electron-irradiated float-zone-refined Si and explained in terms of entropy variations in the configurational space. We believe that the metastability found in the p-GaAs sample is also due to a barrierless transformation of defect configuration, driven by variations in both entropy and the charge state of GaAs. © 2001 American Institute of Physics.
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71.55.Eq III-V semiconductors
81.05.Ea III-V semiconductors
81.10.Fq Growth from melts; zone melting and refining

Gap states of hydrogenated amorphous silicon near and above the threshold of microcrystallinity with subtle boron compensation

Shuran Sheng, Xianbo Liao, and Guanglin Kong

Appl. Phys. Lett. 78, 2509 (2001); http://dx.doi.org/10.1063/1.1368185 (3 pages) | Cited 11 times

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The effects of hydrogen dilution, subtle boron compensation, and light-soaking on the gap states of hydrogenated amorphous silicon films (a-Si:H) near and above the threshold of microcrystallinity have been investigated in detail by the constant photocurrent method and the improved phase-shift analysis of modulated photocurrent technique. It is shown that high hydrogen dilution near the threshold of microcrystallinity leads to a more ordered network structure and to the redistribution of gap states; it gives rise to a small peak at about 0.55 eV and a shoulder at about 1.2 eV below the conduction band edge, which are associated with the formation of microcrystallites embedded in the amorphous silicon host matrix. A concurrent subtle boron compensation is demonstrated to prevent excessive formation of microcrystallinity, and to help promote the growth of the ordered regions and reduce the density of gap defect states, particularly those associated with microcrystallites. Hydrogen-diluted and appropriately boron-compensated a-Si:H films deposited near the threshold of microcrystallinity show the lowest density of the defects in both the annealed and light-soaked states, and hence, the highest performance and stability. © 2001 American Institute of Physics.
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71.55.Cn Elemental semiconductors
72.80.Cw Elemental semiconductors
81.05.Cy Elemental semiconductors
72.80.Ng Disordered solids
73.61.Jc Amorphous semiconductors; glasses
81.05.Gc Amorphous semiconductors
68.55.-a Thin film structure and morphology
73.50.Pz Photoconduction and photovoltaic effects
72.40.+w Photoconduction and photovoltaic effects
71.55.Jv Disordered structures; amorphous and glassy solids
73.61.Cw Elemental semiconductors
71.23.Cq Amorphous semiconductors, metallic glasses, glasses

On the nature of the D1-defect center in SiC: A photoluminescence study of layers grown by solid-source molecular-beam epitaxy

A. Fissel, W. Richter, J. Furthmüller, and F. Bechstedt

Appl. Phys. Lett. 78, 2512 (2001); http://dx.doi.org/10.1063/1.1367883 (3 pages) | Cited 15 times

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Undoped and boron-doped SiC layers are grown on hexagonal SiC(0001) substrates by means of solid-source molecular-beam epitaxy. Hexagonal 4H– and 6H–SiC layers are grown homoepitaxially via step-controlled epitaxy, whereas the cubic 3C–SiC is grown pseudomorphically via nucleation and subsequent step flow. The low-temperature photoluminescence spectra only show the well-known emission lines of the so-called D1 center. The line positions are compared with results of first-principles calculations. The growth conditions, the line shape, and the line shift with the polytype support an interpretation as bound-exciton recombination at a native-defect complex that contains a Si vacancy. © 2001 American Institute of Physics.
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71.55.Ht Other nonmetals
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Hd Other semiconductors
78.66.Li Other semiconductors
68.55.A- Nucleation and growth
78.55.Hx Other solid inorganic materials
61.72.J- Point defects and defect clusters

Thermal-annealing dependence of C-related atomic configuration in Si1−x−yGexCy crystals grown by ultra-high-vacuum chemical-vapor deposition

Y. Kanzawa, T. Saitoh, and M. Kubo

Appl. Phys. Lett. 78, 2515 (2001); http://dx.doi.org/10.1063/1.1367294 (3 pages) | Cited 5 times

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Si1−x−yGexCy crystals were grown by ultra-high-vacuum chemical-vapor deposition and their thermal-annealing behaviors were studied by infrared (IR) absorption measurements. The present samples exhibited absorption peaks originating from local vibrational modes of substitutional C atoms with two different atomic configurations; one is a C atom with four Si neighbors (Si4 configuration) and the other is with one Ge and three Si neighbors (Si3Ge1 configuration). As the annealing temperature was increased from 700 to 950 °C, the absorption peak of the C atoms with Si3Ge1 configuration increased in intensity. This clearly demonstrated that thermal annealing leads to the formation of Ge–C bonds. Moreover, the composition dependence of the IR spectra suggested that Ge–C bonds are formed to reduce the strain energy of the Si1−x−yGexCy crystals. © 2001 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.40.Gh Other heat and thermomechanical treatments
78.66.Li Other semiconductors
78.30.Hv Other nonmetallic inorganics
63.20.Pw Localized modes
61.50.Lt Crystal binding; cohesive energy

Low-frequency photocurrent noise in semiconductors: Effect of nonlinear current–voltage characteristics

Anna Carbone, Piero Mazzetti, and Fausto Rossi

Appl. Phys. Lett. 78, 2518 (2001); http://dx.doi.org/10.1063/1.1368188 (3 pages) | Cited 3 times

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A current noise model for planar metal–semiconductor–metal photodetectors is proposed, which allows one to account for the low-frequency excess-noise behavior measured in several semiconductor devices. According to the proposed model—based on a multiplicative noise mechanism—the photocurrent noise power can be directly related to the carrier density and to the photogeneration level. Moreover, in the absence of potential-barrier fluctuations, the standard 1/n behavior of the simple g–r noise model is recovered. © 2001 American Institute of Physics.
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73.50.Pz Photoconduction and photovoltaic effects
85.60.Gz Photodetectors (including infrared and CCD detectors)
73.40.Sx Metal-semiconductor-metal structures
73.50.Td Noise processes and phenomena

Switching behavior of semiconducting carbon nanotubes under an external electric field

Alain Rochefort, Massimiliano Di Ventra, and Phaedon Avouris

Appl. Phys. Lett. 78, 2521 (2001); http://dx.doi.org/10.1063/1.1367295 (3 pages) | Cited 23 times

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We investigate theoretically the switching characteristics of semiconducting carbon nanotubes connected to gold electrodes under an external (gate) electric field. We find that the external introduction of holes is necessary to account for the experimental observations. We identify metal-induced gap states (MIGS) at the contacts and find that the MIGS of an undoped tube would not significantly affect the switching behavior, even for very short tube lengths. We also explore the miniaturization limits of nanotube transistors, and, on the basis of their switching ratio, we conclude that transistors with channels as short as 50 Å would have adequate switching characteristics. © 2001 American Institute of Physics.
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73.63.Fg Nanotubes

Spectrum dynamics of negative-effective-mass oscillators under terahertz radiation

J. C. Cao, X. L. Lei, A. Z. Li, and H. C. Liu

Appl. Phys. Lett. 78, 2524 (2001); http://dx.doi.org/10.1063/1.1364661 (3 pages) | Cited 13 times

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We report on a theoretical investigation of power spectrum dynamics in negative-effective-mass (NEM) p+pp+ oscillators under the influence of terahertz (THz) electromagnetic radiation. Possible types of transport states (periodic or chaotic) and transitions between them are examined with the intensity and frequency of the radiation as controlling parameters. When the driving frequency is fixed to the self-oscillating frequency times the inverse Golden ratio, the resulting power spectrum pattern displays a very complex mosaic scenario with a self-similar emergence of high-order mixing frequencies. © 2001 American Institute of Physics.
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84.30.Ng Oscillators, pulse generators, and function generators
05.45.Xt Synchronization; coupled oscillators
85.30.Kk Junction diodes
07.57.Hm Infrared, submillimeter wave, microwave, and radiowave sources
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Possible giant magnetoelectric effect of ferromagnetic rare-earth–iron-alloys-filled ferroelectric polymers

Ce Wen Nan, Ming Li, Xiqiao Feng, and Shouwen Yu

Appl. Phys. Lett. 78, 2527 (2001); http://dx.doi.org/10.1063/1.1367293 (3 pages) | Cited 46 times

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Coupled magnetic–mechanical–electric effects in a composite with ferromagnetic rare-earth–iron alloys (e.g., Tb1−xDyxFe2) filled in ferroelectric polymers [e.g, poly(vinylidene-fluoride–trifluoroethylene) copolymer] are studied by using the Green’s function technique. Numerical results suggest a possible giant linear magnetoelectric effect in the ferroic polymer–matrix composite, which is markedly larger than that in the best-known magnetoelectric materials. In addition, the mechanically flexible composite exhibits large magnetostriction. The present results may stimulate further interest in the area of magnetoelectric materials for technological applications. © 2001 American Institute of Physics.
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75.50.Bb Fe and its alloys
75.80.+q Magnetomechanical effects, magnetostriction
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Jd Polymers; organic compounds

Intrinsic exchange biasing in MnAs epilayers grown on (001) GaAs

S. H. Chun, S. J. Potashnik, K. C. Ku, J. J. Berry, P. Schiffer, and N. Samarth

Appl. Phys. Lett. 78, 2530 (2001); http://dx.doi.org/10.1063/1.1367306 (3 pages) | Cited 19 times

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We have studied the magnetic properties of MnAs epilayers grown in two preferred orientations on (001) GaAs by molecular-beam epitaxy. Samples with the (math100) MnAs parallel to (001) GaAs (“type A”) show asymmetric hysteresis loops and an anomalous temperature dependence of the coercive field. We attribute these anomalies to intrinsic exchange biasing effects arising from the presence of a strain-induced antiferromagnetic β-MnAs phase that coexists with the ferromagnetic α-MnAs phase. These unusual effects vanish with decreasing sample thickness, suggesting a strategy for suppressing the antiferromagnetic β-MnAs phase. © 2001 American Institute of Physics.
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75.50.Cc Other ferromagnetic metals and alloys
75.50.Ee Antiferromagnetics
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.70.Ak Magnetic properties of monolayers and thin films
64.70.K- Solid-solid transitions
68.55.-a Thin film structure and morphology
75.30.Et Exchange and superexchange interactions

Inelastic magnon and phonon excitations in Al1−xCox/Al1−xCox-oxide/Al tunnel junctions

Xiu-Feng Han, Junichirou Murai, Yasuo Ando, Hitoshi Kubota, and Terunobu Miyazaki

Appl. Phys. Lett. 78, 2533 (2001); http://dx.doi.org/10.1063/1.1367882 (3 pages) | Cited 12 times

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Magnetoelectric properties of the tunnel junctions, Al(50 nm)/Al2O3(1.2nm)/Al(50nm)(x = 0), Al(55 nm)/Al2O3(1.0nm)/Co(55nm) (x = 0 and top electrode is Co), and Al1−xCox(55 nm)/Al1−xCox-oxide(d nm)/Al(55 nm) (x = 0.25, 0.50, 0.75, and 1.0), were investigated. Oxides of Al1−xCox (x = 0, 0.25, 0.50, 0.75, and 1.0) were chosen as barrier materials in order to modulate the magnon and phonon excitations in the barrier layer and the interfaces. It was shown that the magnon and phonon excitations were the main sources of inelastic scattering in the tunneling processes for the conduction electrons in these tunnel junctions at nonzero bias voltages. The magnon effects were enhanced in the Co-rich barrier junctions. The Al–O–Co phonon energy decreased with increasing Co composition between the Al–O and Co–O phonon energies based on an Al–O–Co stretching mode in the Al1−xCox-oxide barrier as vibrational frequency of crystal lattice decreased with increasing Co composition. © 2001 American Institute of Physics.
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73.40.Rw Metal-insulator-metal structures
75.30.Ds Spin waves
71.38.-k Polarons and electron-phonon interactions
72.10.Di Scattering by phonons, magnons, and other nonlocalized excitations
73.40.Gk Tunneling

Ferroelectricity and ferrimagnetism in iron-doped BaTiO3

R. Maier, J. L. Cohn, J. J. Neumeier, and L. A. Bendersky

Appl. Phys. Lett. 78, 2536 (2001); http://dx.doi.org/10.1063/1.1367311 (3 pages) | Cited 28 times

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The structural and physical properties of pseudocubic thin-film BaTi1−xFexO3(0.5 ⩽ x ⩽ 0.75) grown by pulsed-laser deposition are reported. This material is of interest because the corresponding bulk compounds have hexagonal structure for comparable x, and because the films are both ferroelectric and ferrimagnetic well above room temperature. A substantial increase of the ferroelectric transition temperature relative to that of bulk BaTiO3 is attributed to lattice expansion induced by Fe doping. © 2001 American Institute of Physics.
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77.80.B- Phase transitions and Curie point
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
75.50.Gg Ferrimagnetics
77.55.-g Dielectric thin films
75.70.Ak Magnetic properties of monolayers and thin films
68.55.-a Thin film structure and morphology

Growth of single-domain (Sm0.5Eu0.5)Ba2Cu3O7−δ with high Tc and Jc by employing a thermal gradient

A. Hu, N. Sakai, and M. Murakami

Appl. Phys. Lett. 78, 2539 (2001); http://dx.doi.org/10.1063/1.1367305 (3 pages) | Cited 25 times

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Bulk (Sm0.5Eu0.5)Ba2Cu3O7−δ superconductors were grown isothermally and with a vertical thermal gradient of −5 °C/cm in air. The crystals grown at a large growth rate under the thermal gradient exhibited a high-Tc value of 95 K and a plateau in the Jc–B curve at 1–4 T at 77 K with postannealing in Ar. We found that the substitution of Ba by rare-earth (RE) elements could be suppressed with a large growth rate. The narrow range of RE–Ba solid solution was attributed to the fast crystallization rate of RE1+xBa2−xCu3O7−δ with low-x values. © 2001 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.10.+v Occurrence, potential candidates
74.25.Sv Critical currents
81.10.Fq Growth from melts; zone melting and refining
81.40.Gh Other heat and thermomechanical treatments
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Dielectric properties of strained (Ba, Sr)TiO3 thin films epitaxially grown on Si with thin yttria-stabilized zirconia buffer layer

Sungjin Jun, Young Sung Kim, Jaichan Lee, and Young Woon Kim

Appl. Phys. Lett. 78, 2542 (2001); http://dx.doi.org/10.1063/1.1367309 (3 pages) | Cited 27 times

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We have grown epitaxial (Ba0.5, Sr0.5)TiO3 (BST) thin films on Si with very thin yttria-stabilized zirconia (YSZ) buffer layer. The thin YSZ buffer layer affects the stress state of the epitaxial BST layer as well as the growth behavior of the BST layer, i.e., the degree of epitaxy. The epitaxial BST films grown on Si are in two-dimensional tensile stress. We have found that the dielectric constant of the BST films increased with decreasing the lattice distortion in the state of tensile stress. The dielectric constant of the BST films reaches 1300 when the lattice distortion (surface normal lattice constant/in-plane lattice constant) is 0.993. © 2001 American Institute of Physics.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.-e Ferroelectricity and antiferroelectricity
77.22.Ch Permittivity (dielectric function)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology

Dielectric properties of La3Ga5SiO14 at microwave frequencies between 10 and 400 K

Vincent Giordano, Yann Kersalé, and Jean-Jacques Boy

Appl. Phys. Lett. 78, 2545 (2001); http://dx.doi.org/10.1063/1.1365415 (3 pages) | Cited 2 times

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We report measurements of dielectric permittivity and dielectric losses at microwave frequencies of lanthanum gallium silicate as a function of temperature. The dielectric rod resonator method was used to evaluate the two relative permittivity tensor components ϵt and ϵz of this uniaxial dielectric crystal. Between 10 and 400 K, ϵt varies from 18.92 to 19.65 whereas ϵz ranges from 60.81 to 46.66. Around 300 K, the temperature coefficients of ϵt and ϵz have opposite signs and are equal to 130 and −720 ppm/K, respectively. This characteristic enables one to design a self-compensated microwave resonator presenting a low frequency temperature sensitivity. For the measured dielectric sample the dielectric losses range from 1×10−4 to 5×10−6 between 300 and 20 K and are actually limited by the crystal quality. © 2001 American Institute of Physics.
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77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation
84.30.Ng Oscillators, pulse generators, and function generators
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Changes in the interface capacitance for fatigued lead–zirconate–titanate capacitors

X. J. Meng, J. L. Sun, J. Yu, L. X. Bo, C. P. Jiang, Q. Sun, S. L. Guo, and J. H. Chu

Appl. Phys. Lett. 78, 2548 (2001); http://dx.doi.org/10.1063/1.1367301 (3 pages) | Cited 7 times

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From the capacitance–voltage dependence of Pt/PbZr0.5Ti0.5O3/Pt capacitors, we mathematically separated the capacitance into two parts corresponding to two regions of the samples, the uniform electric-field region and the nonuniform region. They are correlated with the bulk ferroelectric film region and the Pt/PbZr0.5Ti0.5O3 Schottky barrier interface region, respectively. The calculations based on the in-series capacitor model show a slight decrease of dielectric permitivity for the fatigued bulk films. By assuming a much smaller dielectric permitivity of the interface region than that of bulk films, it was found that the interface capacitance decreased remarkably compared with that of the bulk ferroelectric film after fatigue. This decrease was attributed to the lowering of ferroelectricity in the interface layer, which suggests that the fatigue is mainly an interface state controlled process. The asymmetricity in the interface capacitance–voltage curve is attributed to the different defect concentration levels in the top and bottom interface regions. © 2001 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
77.55.-g Dielectric thin films
84.32.Tt Capacitors
77.22.Ch Permittivity (dielectric function)

Piezoelectric properties of 〈001〉 textured Pb(Mg1/3Nb2/3)O3–PbTiO3 ceramics

E. M. Sabolsky, A. R. James, S. Kwon, S. Trolier-McKinstry, and G. L. Messing

Appl. Phys. Lett. 78, 2551 (2001); http://dx.doi.org/10.1063/1.1367291 (3 pages) | Cited 79 times

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The piezoelectric properties of (1−x) Pb(Mg1/3Nb2/3)O3–xPbTiO3 (x = 0.3–0.35), ceramics with a high degree of 〈001〉 fiber texture were investigated for possible actuator applications. Piezoelectric coefficients (d33) in excess of 1200 pC/N associated with strain levels up to >0.3% were observed in samples prepared by a reactive templated grain growth process. No excess PbO was used in the starting composition. A high degree of fiber texture was achieved using 〈001〉 oriented BaTiO3 template particles in a fine-grained precursor for the PMN–32PT matrix. High densities together with texture resulted in a significant increase in strain levels and d33 values compared to their polycrystalline counterparts. Peak dielectric constants on the order of 22 000 with losses of ∼2% and well-saturated hysteresis loops with a Pr ∼ 27 μC/cm2 were recorded on the textured samples. These domain engineered, textured ceramics have tremendous potential for high-performance actuators. © 2001 American Institute of Physics.
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77.65.Bn Piezoelectric and electrostrictive constants
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation
77.80.Dj Domain structure; hysteresis
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Liquid-crystal display of stress fields in ferroelectrics

Doru C. Lupascu, Sergio L. dos Santos e Lucato, Jürgen Rödel, Markus Kreuzer, and Christopher S. Lynch

Appl. Phys. Lett. 78, 2554 (2001); http://dx.doi.org/10.1063/1.1365417 (3 pages) | Cited 4 times

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Direct optical images of local surface potentials generated by the process zone of a crack are shown for a thickness-poled ferroelectric ceramic using liquid crystals. The observed potentials can be mapped to stresses within the material revealing the complex shape and time development of the process zone so far not accessible using other techniques. © 2001 American Institute of Physics.
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77.80.-e Ferroelectricity and antiferroelectricity
77.22.Ej Polarization and depolarization
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Direct patterning of photosensitive low-dielectric-constant films using electron-beam lithography

Takamaro Kikkawa, Tatsuro Nagahara, and Hideki Matsuo

Appl. Phys. Lett. 78, 2557 (2001); http://dx.doi.org/10.1063/1.1360777 (3 pages) | Cited 4 times

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A direct patterning technique of interlayer dielectric films was developed for multilevel interconnections. A photosensitive methylsilazane film with a dielectric constant of 2.7 was synthesized. A methylsilazane precursor consists of a photoacid generator, a sensitizer, and a base polymer. The photosensitive methylsilazane film could be patterned by use of electron-beam lithography or ultraviolet lithography. It was demonstrated that the smallest feature size of 50 nm for damascene lines and via holes could be directly patterned in these films by electron-beam lithography. © 2001 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
77.55.-g Dielectric thin films
77.84.Jd Polymers; organic compounds
85.40.Hp Lithography, masks and pattern transfer
77.22.Ch Permittivity (dielectric function)

Characterization of electrical conduction in silicon nanowire by scanning Maxwell-stress microscopy

Hideo Fujii, Takashi Matsukawa, Seigo Kanemaru, Hiroshi Yokoyama, and Junji Itoh

Appl. Phys. Lett. 78, 2560 (2001); http://dx.doi.org/10.1063/1.1365416 (3 pages) | Cited 15 times

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An experimental approach to investigate anomalous electrical conduction in a 100 nm width silicon wire by scanning Maxwell-stress microscopy (SMM) has been reported. The silicon wire exhibited negative resistance and hysteresis characteristics by sweeping the applied voltage up to 50 V. Potential profile along the wire obtained from the SMM images exhibited that lateral electric field significantly increased at the ground-side end of the wire after the hysteresis characteristics emerged. The field increase is interpreted as the conductivity decrease. The origin of the conductance decrease is considered to be generation and trapping of hot holes at the ground-side end. © 2001 American Institute of Physics.
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73.61.Cw Elemental semiconductors
73.50.Fq High-field and nonlinear effects
73.63.Nm Quantum wires

Local structure of Ge nanoislands on Si(111) surfaces with a SiO2 coverage

Alexander V. Kolobov, Alexander A. Shklyaev, Hiroyuki Oyanagi, Paul Fons, Satoshi Yamasaki, and Masakazu Ichikawa

Appl. Phys. Lett. 78, 2563 (2001); http://dx.doi.org/10.1063/1.1367287 (3 pages) | Cited 23 times

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We have investigated the local structure and photoluminescence properties of ultrasmall Ge islands grown on Si(111) covered with SiO2. Scanning electron microscopy and transmission electron microscopy measurements show that the islands have a hemispherical shape, and depending on the growth temperature, can be either epitaxial or nonepitaxial. X-ray absorption near-edge structure measurements demonstrate that the nonepitaxial islands have the local structure of bulk diamond Ge and are very stable towards oxidation. The epitaxial islands are found to be partly oxidized, but no alloying with the Si substrate is observed. The nonepitaxial islands exhibit a photoluminescence peaked at 2.3 eV, which is typical of Ge nanocrystals embedded in SiO2. Possible mechanisms for the stability of the nonepitaxial Ge islands towards oxidation are discussed. © 2001 American Institute of Physics.
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68.55.-a Thin film structure and morphology
78.55.Ap Elemental semiconductors
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
61.46.-w Structure of nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.07.Bc Nanocrystalline materials
78.70.Dm X-ray absorption spectra
81.65.Mq Oxidation
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