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18 Oct 1999

Volume 75, Issue 16, pp. 2347-2507

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Improved ultraviolet quantum efficiency using a semitransparent recessed window AlGaN/GaN heterojunction p-i-n photodiode

T. Li, A. L. Beck, C. Collins, R. D. Dupuis, J. C. Campbell, J. C. Carrano, M. J. Schurman, and I. A. Ferguson

Appl. Phys. Lett. 75, 2421 (1999); http://dx.doi.org/10.1063/1.125034 (3 pages) | Cited 16 times

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We report on the improved quantum efficiency of GaN-based ultraviolet heterojunction photodiodes using a semitransparent recessed window device structure. At a reverse bias of −5 V the quantum efficiency was ∼57% at the band edge, and remained relatively flat down to ∼330 nm after which some absorption in the p-AlGaN layer became evident. The quantum efficiency only gradually declines after this point, remaining >20% at 280 nm. We attribute these results to avoidance of the optical dead space at the surface of GaN homojunction p-i-ns. The semitransparent p-AlGaN layer was comparatively resistive, causing an electric field crowding effect which resulted in a spatially nonuniform temporal behavior. © 1999 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors
81.05.Ea III-V semiconductors

The role of oxygen on the stability of gettering of metals to cavities in silicon

J. S. Williams, M. J. Conway, J. Wong-Leung, P. N. K. Deenapanray, M. Petravic, R. A. Brown, D. J. Eaglesham, and D. C. Jacobson

Appl. Phys. Lett. 75, 2424 (1999); http://dx.doi.org/10.1063/1.125035 (3 pages) | Cited 12 times

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The effect of oxygen implanted into epitaxial Si layers on the ability to getter Au to nanocavities, previously formed by H implantation and annealing, has been studied by Rutherford backscattering, transmission electron microscopy, and secondary ion mass spectrometry. We demonstrate that oxygen is gettered to cavities during extended annealing at 950 °C. Furthermore, the arrival of oxygen at cavities is not only shown to inhibit subsequent attempts to getter Au to cavities, but also to eject chemisorbed Au from the cavity walls. Similar behavior is observed in Czochralski Si, where the source of oxygen is within the Si itself. © 1999 American Institute of Physics.
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81.05.Cy Elemental semiconductors
61.72.Yx Interaction between different crystal defects; gettering effect
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
85.40.Ry Impurity doping, diffusion and ion implantation technology
61.72.Cc Kinetics of defect formation and annealing
61.72.uf Ge and Si
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
68.60.Dv Thermal stability; thermal effects
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Electron energy dependence of metal-oxide-semiconductor degradation

D. J. DiMaria

Appl. Phys. Lett. 75, 2427 (1999); http://dx.doi.org/10.1063/1.125036 (2 pages) | Cited 19 times

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Using a variety of electron injection techniques, defect generation and degradation in thin gate oxide devices are unequivocally shown to be related to the electron energy of the carriers impinging on the silicon contacts to the oxide layer and not due to the oxide electric field. Also, nonuniform channel-hot-electron degradation is shown to be due to the same fundamental mechanism as that observed under uniform degradation conditions using either direct tunneling, Fowler–Nordheim tunneling, or substrate-hot-electron injection. Additive defect generation from all three degradation modes is discussed in terms of realistic device operation. © 1999 American Institute of Physics.
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85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
66.35.+a Quantum tunneling of defects
72.20.Ht High-field and nonlinear effects
73.50.Fq High-field and nonlinear effects

Nanomachining of (110)-oriented silicon by scanning probe lithography and anisotropic wet etching

F. S.-S. Chien, C.-L. Wu, Y.-C. Chou, T. T. Chen, S. Gwo, and W.-F. Hsieh

Appl. Phys. Lett. 75, 2429 (1999); http://dx.doi.org/10.1063/1.125037 (3 pages) | Cited 44 times

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We have demonstrated that silicon nanostructures with high aspect ratios, having ∼ 400 nm structural height and ∼ 55 nm lateral dimension, may be fabricated by scanning probe lithography and aqueous KOH orientation-dependent etching on the H-passivated (110) Si wafer. The high spatial resolution of fabricated features is achieved by using the atomic force microscope based nano-oxidation process in ambient. Due to the large (110)/(111) anisotropic ratio of etch rate and the large Si/SiO2 etch selectivity at a relatively low etching temperature and an optimal KOH concentration, high-aspect-ratio gratings with (111)-oriented structural sidewalls as well as hexagonal etch pit structures determined by the terminal etch geometry can be obtained. © 1999 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.05.Cy Elemental semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
85.40.Hp Lithography, masks and pattern transfer
81.65.Mq Oxidation
82.20.Pm Rate constants, reaction cross sections, and activation energies
42.79.Dj Gratings
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Conduction mechanism under quasibreakdown of ultrathin gate oxide

Y. D. He, Hao Guan, M. F. Li, Byung Jin Cho, and Zhong Dong

Appl. Phys. Lett. 75, 2432 (1999); http://dx.doi.org/10.1063/1.125038 (3 pages) | Cited 4 times

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The conduction mechanism under quasibreakdown of ultrathin gate oxide has been studied systematically in both n and p metal–oxide–semiconductor field effect transistors (MOSFETs) with a 3.7 nm gate oxide. The carrier separation experiment is conducted to investigate the evolutions of gate, source/drain, and substrate currents before and after quasibreakdown. It is shown that after quasibreakdown, the substrate current and the source-drain current versus the gate voltage curves are surprisingly analogous to those curves observed in fresh MOSFET with a gate oxide of direct tunneling thickness. This strongly supports the quasibreakdown model based on the local physically damaged region by which the effective oxide thickness is reduced. When direct tunnelings of conduction band electrons, valence band electrons and holes through the effectively thinned gate oxide are taken into account, the major experimental observations in the quasibreakdown can be explained in a unified way. © 1999 American Institute of Physics.
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85.30.Tv Field effect devices
73.40.Gk Tunneling
85.30.De Semiconductor-device characterization, design, and modeling

Direct measurement of minority carriers diffusion length using Kelvin probe force microscopy

T. Meoded, R. Shikler, N. Fried, and Y. Rosenwaks

Appl. Phys. Lett. 75, 2435 (1999); http://dx.doi.org/10.1063/1.125039 (3 pages) | Cited 25 times

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We report on the use of Kelvin force microscopy as a method for measuring very short minority carrier diffusion length in semiconductors. The method is based on measuring the surface photovoltage between the tip of an atomic force microscope and the surface of an illuminated semiconductor junction. The photogenerated carriers diffuse to the junction, and change the contact potential difference between the tip and the sample as a function of the distance from the junction edge. The diffusion length L is then obtained by fitting the measured contact potential difference using the minority carrier continuity equation. The method is applied to measurements of electron diffusion lengths in GaP epilayers. © 1999 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Carrier pocket engineering applied to “strained” Si/Ge superlattices to design useful thermoelectric materials

T. Koga, X. Sun, S. B. Cronin, and M. S. Dresselhaus

Appl. Phys. Lett. 75, 2438 (1999); http://dx.doi.org/10.1063/1.125040 (3 pages) | Cited 22 times

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The concept of carrier pocket engineering is applied to strained Si/Ge superlattices to obtain a large thermoelectric figure of merit ZT. In this system, the effect of the lattice strain at the Si/Ge interfaces provides another degree of freedom to control the conduction band structure of the superlattice. We explore various geometries and structures to optimize ZT for the whole three-dimensional superlattice. The resultant ZT, calculated for a symmetrized Si(20 Å)/Ge(20 Å) superlattice grown on a (111) oriented Si0.5Ge0.5 substrate, is 0.96 at 300 K and is shown to increase significantly at elevated temperatures. Such a superlattice can be grown using molecular beam epitaxy. © 1999 American Institute of Physics.
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73.61.Cw Elemental semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
72.20.Pa Thermoelectric and thermomagnetic effects
73.50.Lw Thermoelectric effects

The influence of Mg doping on the formation of Ga vacancies and negative ions in GaN bulk crystals

K. Saarinen, J. Nissilä, P. Hautojärvi, J. Likonen, T. Suski, I. Grzegory, B. Lucznik, and S. Porowski

Appl. Phys. Lett. 75, 2441 (1999); http://dx.doi.org/10.1063/1.125041 (3 pages) | Cited 43 times

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Gallium vacancies and negative ions are observed in GaN bulk crystals by applying positron lifetime spectroscopy. The concentration of Ga vacancies decreases with increasing Mg doping, as expected from the behavior of the VGa formation energy as a function of the Fermi level. The concentration of negative ions correlates with that of Mg impurities determined by secondary ion mass spectrometry. We thus attribute the negative ions to MgGa−. The negative charge of Mg suggests that Mg doping converts n-type GaN to semi-insulating mainly due to the electrical compensation of ON+ donors by MgGa− acceptors. © 1999 American Institute of Physics.
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61.72.J- Point defects and defect clusters
78.70.Bj Positron annihilation
61.72.S- Impurities in crystals
71.55.Eq III-V semiconductors
81.05.Ea III-V semiconductors

Polarization-enhanced Mg doping of AlGaN/GaN superlattices

Peter Kozodoy, Yulia P. Smorchkova, Monica Hansen, Huili Xing, Steven P. DenBaars, Umesh K. Mishra, A. W. Saxler, R. Perrin, and W. C. Mitchel

Appl. Phys. Lett. 75, 2444 (1999); http://dx.doi.org/10.1063/1.125042 (3 pages) | Cited 51 times

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The hole-transport properties of Mg-doped AlGaN/GaN superlattices are carefully examined. Variable-temperature Hall-effect measurements indicate that the use of such superlattices enhances the average hole concentration at a temperature of 120 K by over five orders of magnitude compared to a bulk GaN film (the enhancement at room temperature is a factor of 9). An unusual modulation-doping scheme, which has been realized using molecular-beam epitaxy, has yielded high-hole-mobility superlattices and conclusively demonstrated the pivotal role of piezoelectric and spontaneous polarization in determining the band structure of the superlattices. © 1999 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
77.65.-j Piezoelectricity and electromechanical effects
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.22.Ej Polarization and depolarization
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Controlled Li doping of Si nanowires by electrochemical insertion method

G. W. Zhou, H. Li, H. P. Sun, D. P. Yu, Y. Q. Wang, X. J. Huang, L. Q. Chen, and Z. Zhang

Appl. Phys. Lett. 75, 2447 (1999); http://dx.doi.org/10.1063/1.125043 (3 pages) | Cited 30 times

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Si nanowires (NWs) were doped with large amounts of Li+ ions by an electrochemical insertion method at room temperature. Si NWs with different doping levels were obtained by controlling the discharging/charging of Li/Si NWs cell. The microstructures of Si NWs with different doses of Li+ ions were investigated by high-resolution electron microscopy. The crystalline structure of the Si NWs was destroyed gradually with the increasing of Li+ ion dose. When the Li+ ions were extracted from the amorphous Li-doped Si NWs by the same electrochemical method, local ordering of atoms occurred and recrystallization was observed. The photoluminescence peak and intensity of Li+-doped Si NWs are closely related to the doping dose. © 1999 American Institute of Physics.
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61.72.uf Ge and Si
78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
82.45.-h Electrochemistry and electrophoresis
82.30.Nr Association, addition, insertion, cluster formation

Stress measurements using ultraviolet micro-Raman spectroscopy

K. F. Dombrowski, I. De Wolf, and B. Dietrich

Appl. Phys. Lett. 75, 2450 (1999); http://dx.doi.org/10.1063/1.125044 (2 pages) | Cited 14 times

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We present measurements of mechanical stress in silicon device structures by ultraviolet (UV) micro-Raman spectroscopy. The shorter wavelength of the UV light (364 nm) is the basis for two major improvements over conventionally used blue light (458 nm): The smaller penetration depth of only 15 nm (vs 300 nm for blue light) probes the stress very close to the surface, and a smaller laser spot on the sample (0.7 μm vs 0.9 μm) results in higher spatial resolution. A comparison of stress patterns obtained in the same sample with 364 nm (UV) and 458 nm (blue) light demonstrates that areas of high stress, which are averaged out by longer wavelength light, can be detected with UV light. © 1999 American Institute of Physics.
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46.80.+j Measurement methods and techniques in continuum mechanics of solids
81.70.Fy Nondestructive testing: optical methods
78.30.-j Infrared and Raman spectra

In-plane gate single-electron transistor in Ga[Al]As fabricated by scanning probe lithography

S. Lüscher, A. Fuhrer, R. Held, T. Heinzel, K. Ensslin, and W. Wegscheider

Appl. Phys. Lett. 75, 2452 (1999); http://dx.doi.org/10.1063/1.125045 (3 pages) | Cited 22 times

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A single-electron transistor has been realized in a Ga[Al]As heterostructure by oxidizing lines in the GaAs cap layer with an atomic force microscope. The oxide lines define the boundaries of the quantum dot, the in-plane gate electrodes, and the contacts of the dot to source and drain. Both the number of electrons in the dot as well as its coupling to the leads can be tuned with an additional, homogeneous top gate electrode. Pronounced Coulomb blockade oscillations are observed as a function of voltages applied to different gates. We find that, for positive top-gate voltages, the lithographic pattern is transferred with high accuracy to the electron gas. Furthermore, the dot shape does not change significantly when in-plane voltages are tuned. © 1999 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.23.Hk Coulomb blockade; single-electron tunneling
85.35.Ds Quantum interference devices
85.40.Hp Lithography, masks and pattern transfer
07.79.Lh Atomic force microscopes

Large-scale synthesis of single crystalline gallium nitride nanowires

G. S. Cheng, L. D. Zhang, Y. Zhu, G. T. Fei, L. Li, C. M. Mo, and Y. Q. Mao

Appl. Phys. Lett. 75, 2455 (1999); http://dx.doi.org/10.1063/1.125046 (3 pages) | Cited 136 times

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Large-scale synthesis of single crystalline GaN nanowires in anodic alumina membrane was achieved through a gas reaction of Ga2O vapor with a constant flowing ammonia atmosphere at 1273 K. X-ray diffraction, Raman backscattering spectroscopy, scanning electron microscopy, and transmission electron microscopy indicated that those GaN nanowires with hexagonal wurtzite structure were about 14 nm in diameter and up to several hundreds of micrometers in length. The growth mechanism of the single crystalline GaN nanowires is discussed. © 1999 American Institute of Physics.
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81.05.Ea III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Surface micro-roughness and transport properties of Si delta-doped GaAs/InxGa1−xAs/GaAs (0.1 ⩽ × ⩽ 0.25) quantum wells grown by molecular-beam epitaxy on GaAs (001) and GaAs (111)B

M. Zervos, M. Elliott, and D. I. Westwood

Appl. Phys. Lett. 75, 2458 (1999); http://dx.doi.org/10.1063/1.125047 (3 pages) | Cited 1 time

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We investigated the surface quality and electron transport properties of 200 Å GaAs/InxGa1−xAs/GaAs, 0.1 ⩽ x ⩽ 0.25, quantum well structures grown by molecular-beam epitaxy on GaAs (001) and (111)B, center delta-doped with Si to 1×1013 cm−2. For GaAs barriers grown above 600 °C, room temperature atomic force microscopy of the (111)B samples showed a surface micro roughness below 2 Å for x ⩽ 0.15 but reaching 60 Å for x = 0.25. In addition, analysis of Shubnikov–de Haas and Hall effects at 4.2 K showed a strong deterioration of the electrical properties. In contrast, the (001) structures had surface micro roughness below 2 Å and superior transport properties even at x = 0.25. At lower growth temperatures the surface morphology roughened, but without a commensurate deterioration of the electrical properties. For the (001) layers self-consistent Poisson–Schrödinger calculations give quantum well subband densities in good agreement with those measured, assuming full incorporation of Si substitutional donors. However, a 20% loss of carriers was observed in the (111) layers, and the excited state subband densities were a smaller fraction of the ground subband occupancy compared to the (001). Amphoteric (Si-on-As sites) behavior is believed responsible for this behavior. © 1999 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.61.Ey III-V semiconductors
81.05.Ea III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Ct Interface structure and roughness
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Observation of carrier depletion and emission effects on capacitance dispersion in relaxed In0.2Ga0.8As/GaAs quantum wells

J. F. Chen, P. Y. Wang, C. Y. Tsai, J. S. Wang, and N. C. Chen

Appl. Phys. Lett. 75, 2461 (1999); http://dx.doi.org/10.1063/1.125048 (3 pages) | Cited 1 time

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Strong changes in capacitance over frequency are found for highly relaxed In0.2Ga0.8As/GaAs quantum well. The high-frequency dispersion is explained by a resistance–capacitance time constant effect due to the existence of a high resistive layer while the low-frequency dispersion is due to carrier emission from traps. The high-resistance layer is created by carrier depletion when InGaAs thickness increases beyond the critical thickness. Excellent agreement is found between the data from capacitance–frequency spectra and deep-level transient spectroscopy, permitting us to conclude that both the carrier depletion and emission effects observed in capacitance–frequency spectra are due to the existence of an acceptor trap at 0.33 eV. This trap is generated when the InGaAs thickness is beyond its critical thickness and is due to defect states associated with misfit dislocations. © 1999 American Institute of Physics.
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73.61.Ey III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
71.55.Eq III-V semiconductors
72.80.Ey III-V and II-VI semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Controlled agglomeration of Tb-doped Y2O3 nanocrystals studied by x-ray absorption fine structure, x-ray excited luminescence, and photoluminescence

Y. L. Soo, S. W. Huang, Y. H. Kao, V. Chhabra, B. Kulkarni, J. V. D. Veliadis, and R. N. Bhargava

Appl. Phys. Lett. 75, 2464 (1999); http://dx.doi.org/10.1063/1.125049 (3 pages) | Cited 20 times

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Local environment surrounding Y atoms in Y2O3:Tb nanocrystals under various heat treatment conditions has been investigated by using the extended x-ray absorption fine structure (EXAFS) technique. X-ray excited luminescence (XEL) with the incident x-ray energy near Y K edge and Tb L edges has also been measured to investigate the mechanisms of x-ray-to-visible down conversion in these doped nanoparticles. The observed changes in EXAFS, XEL, and photoluminescent data can be explained on the basis of increased average size of the nanoparticles as confirmed by transmission electron microscopy studies. Our results thus demonstrate that the doped nanoparticles can agglomerate to a controllable degree by varying the heat treatment temperature. At higher temperatures, the local environment surrounding Y atoms in the nanoparticles is found to become similar to that in bulk Y2O3 while the XEL output still shows the characteristics of nanocrystals. These results indicate that appropriate heat treatment can afford an effective means to control the intensity and signal-to-background ratio of green luminescence output of these doped nanocrystal phosphors, potentially useful for some device applications. © 1999 American Institute of Physics.
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78.70.Dm X-ray absorption spectra
78.55.Hx Other solid inorganic materials

Energy spectrum of surface states of lattice-matched In0.52Al0.48As surface intrinsic-n+ structure

J. S. Hwang, W. C. Hwang, Z. P. Yang, G. S. Chang, J. I. Chyi, and N. T. Yeh

Appl. Phys. Lett. 75, 2467 (1999); http://dx.doi.org/10.1063/1.125050 (3 pages) | Cited 8 times

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This work uses photoreflectance to investigate the band gap, built-in electric field, and surface Fermi level of a series of lattice-matched In0.52Al0.48As surface intrinsic-n+ structures having different undoped layer thickness. Experimental results indicate that the surface Fermi level is weakly pinned. By converting the dependence of the built-in electric field on undoped layer thickness into the dependence of surface state density on the surface Fermi level, this study defines the energy spectrum of the surface state density of InAlAs surface using a Gaussian distribution function. © 1999 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
78.20.-e Optical properties of bulk materials and thin films
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
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Atomic structure and composition of the barrier in the modified interface high-Tc Josephson junction studied by transmission electron microscopy

J. G. Wen, N. Koshizuka, S. Tanaka, T. Satoh, M. Hidaka, and S. Tahara

Appl. Phys. Lett. 75, 2470 (1999); http://dx.doi.org/10.1063/1.125051 (3 pages) | Cited 21 times

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The atomic structure and composition of modified interface junctions which showed reproducible critical current Ic (Ic1σ<8% for 100 junctions) are investigated by transmission electron microscopy. Transmission electron microscopic observations show the existence of a thin barrier (1–2 nm) homogeneously covering the ion milled edge of the base YBa2Cu3Oy film although there is no barrier deposition and annealing process. High-resolution electron microscopy images and energy dispersive x-ray analysis with a spot size of 1 nm indicates that the barrier is a Ba-based perovskite-like structure, (Y1−xCux)BaOy with x<0.5. A thin amorphous layer whose composition deviates from YBa2Cu3Oy is formed due to the preferential sputtering of Cu. The amorphous layer recrystallizes into the nonequilibrium phase (Y1−xCux)BaOy after heating up to the deposition temperature. © 1999 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
74.50.+r Tunneling phenomena; Josephson effects
68.35.Ct Interface structure and roughness
85.25.Cp Josephson devices
74.25.Sv Critical currents
68.35.Fx Diffusion; interface formation
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition

Domain structure of magnetic layers deposited on patterned silicon

S. Landis, B. Rodmacq, B. Dieny, B. Dal’Zotto, S. Tedesco, and M. Heitzmann

Appl. Phys. Lett. 75, 2473 (1999); http://dx.doi.org/10.1063/1.125052 (3 pages) | Cited 25 times

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Arrays of Si square dots down to 200 nm in size were patterned on silicon substrates, and thin films of different magnetic materials were sputter deposited on these patterned substrates. The magnetic film covers the top of the dots, the bottom of the grooves and to much less extent the sidewalls of the dots. Single domain magnetic dots were obtained for Co/NiO bilayers and Co/Pt multilayers, without significant direct coupling mediated by the magnetic deposit on the sidewalls of the dots. Our results indicate that, in these arrays, the magnetic pinning forces are stronger than the estimated value of the largest demagnetizing magnetostatic field on each individual dot. As a result, any magnetic configuration could in principle be stored in such arrays. This approach seems therefore very promising for the preparation of magnetic storage media with ultrahigh density. © 1999 American Institute of Physics.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)

Switching of vertical giant magnetoresistance devices by current through the device

K. Bussmann, G. A. Prinz, S.-F. Cheng, and D. Wang

Appl. Phys. Lett. 75, 2476 (1999); http://dx.doi.org/10.1063/1.125053 (3 pages) | Cited 69 times

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Experiments are reported that demonstrate current-perpendicular-to-the-plane giant magnetoresistance devices can be switched repeatably between the high- and low-resistance states by passing current vertically through the structure. The lithographically patterned devices, having diameters in the range of 0.3–0.7 μm, operate at room temperature and exhibit distinctly separate switching of the soft and hard layers. Designs for magnetoelectronic random access memory can utilize this scheme for storing and reading information. © 1999 American Institute of Physics.
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75.47.De Giant magnetoresistance
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
84.30.Sk Pulse and digital circuits

LaNiO3 buffer layers for high critical current density YBa2Cu3O7−δ and Tl2Ba2CaCu2O8−δ films

C. M. Carlson, P. A. Parilla, M. P. Siegal, D. S. Ginley, Y.-T. Wang, R. D. Blaugher, J. C. Price, D. L. Overmyer, and E. L. Venturini

Appl. Phys. Lett. 75, 2479 (1999); http://dx.doi.org/10.1063/1.125054 (3 pages) | Cited 1 time

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We demonstrate high critical current density superconducting films of YBa2Cu3O7−δ (YBCO) and Tl2Ba2CaCu2O8−δ (Tl-2212) using LaNiO3 (LNO) buffer layers. YBCO films grown on an LNO buffer layer have only a slightly lower Jc (5 K, H = 0) than films grown directly on a bare LaAlO3 substrate. YBCO films grown on LNO buffer layers exhibit minor microstructural disorder and enhanced flux pinning. LNO-buffered Tl-2212 samples show large reductions in Jc at all temperatures and fields compared to those grown on bare LaAlO3, correlating to both a-axis grain and nonsuperconducting phase formation. LNO could be a promising buffer layer for both YBCO and Tl-based superconducting films in coated conductor applications. © 1999 American Institute of Physics.
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74.25.Sv Critical currents
74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
68.55.-a Thin film structure and morphology
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In situ video observation of 180° domain kinetics in congruent LiNbO3 crystals

Venkatraman Gopalan, Q. X. Jia, and T. E. Mitchell

Appl. Phys. Lett. 75, 2482 (1999); http://dx.doi.org/10.1063/1.125055 (3 pages) | Cited 42 times

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We report in situ observation of the nucleation and growth of ferroelectric 180° domains in congruent LiNbO3 crystals. The domains nucleate and grow as six-sided polygons. The wall velocity measured at a constant field shows a spike-like behavior with time, suggesting a strong pinning–depinning type of growth mechanism. This behavior is similar to the corresponding transient current measurement which also shows current spikes during domain reversal. © 1999 American Institute of Physics.
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77.80.Dj Domain structure; hysteresis

Dielectric properties of metal-organic chemical vapor deposited highly textured Pb(ScTa)1−xTixO3 (x = 0–0.3) relaxor ferroelectric thin films on LaNiO3 electrode buffered Si

C. H. Lin, S. W. Lee, Haydn Chen, and T. B. Wu

Appl. Phys. Lett. 75, 2485 (1999); http://dx.doi.org/10.1063/1.125056 (3 pages) | Cited 7 times

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Highly (100) textured Pb(ScTa)1−xTixO3 (x = 0–0.3) thin films were grown on LaNiO3/Pt/Ti electrode-coated Si substrate using metal-organic chemical vapor deposition at 685 °C. Ti addition was introduced to modify the dielectric properties. Diffuse phase transition, typical of relaxor ferroelectrics was noticed. As Ti content increased from 0% to 30%, the phase transition temperature (Tmax) gradually shifted from −10 to 120 °C with the dielectric constant at Tmax increased from 1397 to 1992 (1 kHz). Loss tangent values are generally below 0.025. © 1999 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology
77.80.B- Phase transitions and Curie point
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation

High-displacement spiral piezoelectric actuators

F. Mohammadi, A. L. Kholkin, B. Jadidian, and A. Safari

Appl. Phys. Lett. 75, 2488 (1999); http://dx.doi.org/10.1063/1.125057 (3 pages) | Cited 15 times

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A high-displacement piezoelectric actuator, employing spiral geometry of a curved piezoelectric strip is described. The monolithic actuators are fabricated using a layered manufacturing technique, fused deposition of ceramics, which is capable of prototyping electroceramic components with complex shapes. The spiral actuators (2–3 cm in diameter) consisted of 4–5 turns of a lead zirconate titanate ceramic strip with an effective length up to 28 cm. The width was varied from 0.9 to 1.75 mm with a height of 3 mm. When driven by the electric field applied across the width of the spiral wall, the tip of the actuator was found to displace in both radial and tangential directions. The tangential displacement of the tip was about 210 μm under the field of 5 kV/cm. Both the displacement and resonant frequency of the spirals could be tailored by changing the effective length and wall width. The blocking force of the actuator in tangential direction was about 1 N under the field of 5 kV/cm. These properties are advantageous for high-displacement low-force applications where bimorph or monomorph actuators are currently employed. © 1999 American Institute of Physics.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
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)
77.65.-j Piezoelectricity and electromechanical effects
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Possible cooling by resonant Fowler-Nordheim emission

Alexander N. Korotkov and Konstantin K. Likharev

Appl. Phys. Lett. 75, 2491 (1999); http://dx.doi.org/10.1063/1.125058 (3 pages) | Cited 26 times

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A method of electronic refrigeration based on resonant Fowler-Nordheim emission is analyzed. In this method, a bulk emitter is covered with a-few-nm-thick film of a widegap semiconductor, creating an intermediate step between electron energies in the emitter and in vacuum. An external electric field tilts this potential profile, forming a quantum well at the semiconductor-vacuum boundary. Alignment of its lowest two-dimensional subband with the energy of the hottest electrons of the emitter (a few kBT above the Fermi level) leads to a resonant, selective emission of these electrons, providing emitter cooling. Calculations show that cooling power of at least 30 W/cm2, and temperatures down to 10 K may be achieved using this effect. © 1999 American Institute of Physics.
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07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
79.40.+z Thermionic emission
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.61.-r Electrical properties of specific thin films
73.23.-b Electronic transport in mesoscopic systems
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