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12 Mar 2001

Volume 78, Issue 11, pp. 1463-1639

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Effects of GaAlN barriers and of dimensionality on optical recombination processes in InGaN quantum wells and quantum boxes

P. Lefebvre, T. Taliercio, A. Morel, J. Allègre, M. Gallart, B. Gil, H. Mathieu, B. Damilano, N. Grandjean, and J. Massies

Appl. Phys. Lett. 78, 1538 (2001); http://dx.doi.org/10.1063/1.1352664 (3 pages) | Cited 34 times

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We compare several InGaN-based low-dimensional systems, by time-resolved photoluminescence (PL), versus temperature (8<T<280 K). We investigate the influence of growing or not an AlGaN barrier on top of the active layer. We address the differences between quantum wells and quantum boxes 5–10 nm in diameter and 2 nm in height. Our results are consistent with carrier localization on potential fluctuations with spatial extension much smaller than the size of the quantum boxes. Growing an AlGaN barrier reduces the carrier mobility between fluctuations, thus maintaining an effective PL dominated by localized carriers up to room temperature. © 2001 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
68.65.Fg Quantum wells
68.65.Hb Quantum dots (patterned in quantum wells)
78.47.-p Spectroscopy of solid state dynamics

High-resolution spectral hole burning in CdSe/ZnS core/shell nanocrystals

Phedon Palinginis and Hailin Wang

Appl. Phys. Lett. 78, 1541 (2001); http://dx.doi.org/10.1063/1.1355666 (3 pages) | Cited 27 times

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We report studies of the homogeneous linewidth in CdSe/ZnS core/shell nanocrystals by means of high-resolution spectral hole burning under low excitation levels. The hole burning spectrum reveals a sharp spectral hole as well as clearly resolved acoustic phonon sidebands. Homogeneous linewidths as narrow as 32 μeV were obtained. At low temperature, the temperature dependence of the homogeneous linewidth deviates from the usual linear dependence, reflecting the effects of phonon quantization. © 2001 American Institute of Physics.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
42.50.Hz Strong-field excitation of optical transitions in quantum systems; multiphoton processes; dynamic Stark shift
61.46.-w Structure of nanoscale materials

Origins of threading dislocations in GaN epitaxial layers grown on sapphire by metalorganic chemical vapor deposition

V. Narayanan, K. Lorenz, Wook Kim, and S. Mahajan

Appl. Phys. Lett. 78, 1544 (2001); http://dx.doi.org/10.1063/1.1352699 (3 pages) | Cited 37 times

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The origins of threading dislocations (TDs) in GaN epitaxial layers grown on (0001) sapphire have been investigated by examining different stages of high-temperature (HT) GaN growth on low-temperature GaN nucleation layers (NLs) by transmission electron microscopy. Results indicate that after 20 s of HT growth, GaN islands were free of TDs. After 75 and 120 s of growth, most of the islands contained pure screw (c type) and pure edge (a type) TDs with an interspersion of mixed (c+a type) TDs. Most of the TDs originated from faulted regions located within NLs. TDs move toward the island top surface (c type) or curve toward island side facets (a, c+a type). Coalescence of HT GaN islands did not give rise to either a, c, or c+a type TDs. After 240 s of growth, most TDs were predominantly of a type and could result from climb and glide of basal plane (BP) dislocations that form by the dissociation of Shockley partials located within the faulted regions. BP dislocations are also observed attached to the side facets of islands away from the faulted regions and their possible origins are discussed. c and c+a type TDs form primarily by the coalescence of Frank partials near the GaN/sapphire interface. © 2001 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.05.Ea III-V semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Lk Linear defects: dislocations, disclinations
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.-a Thin film structure and morphology
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Electrophoresis deposition of carbon nanotubes for triode-type field emission display

W. B. Choi, Y. W. Jin, H. Y. Kim, S. J. Lee, M. J. Yun, J. H. Kang, Y. S. Choi, N. S. Park, N. S. Lee, and J. M. Kim

Appl. Phys. Lett. 78, 1547 (2001); http://dx.doi.org/10.1063/1.1349870 (3 pages) | Cited 103 times

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A triode-type field emission display has been fabricated using carbon nanotube emitters. Purified single walled carbon nanotubes were selectively deposited onto a cathode electrode in a triode-type structure by an electrophoresis. Emission current was modulated with gate potentials of 100–300 V. A high brightness of 1000 cd/m2 with uniform emission was obtained at 900 V at the anode and 200 V at the gate. The fluctuation of emission current was found to be less than 5% in a fully sealed field emission display. Selective deposition of carbon nanotubes by electrophoresis shows high feasibility for triode-type field emission displays. © 2001 American Institute of Physics.
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81.07.De Nanotubes
85.35.Kt Nanotube devices
85.45.Fd Field emission displays (FEDs)
61.46.-w Structure of nanoscale materials
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
81.05.ub Fullerenes and related materials
82.45.Qr Electrodeposition and electrodissolution

Limits on the Curie temperature of (III,Mn)V ferromagnetic semiconductors

John Schliemann, Jürgen König, Hsiu-Hau Lin, and Allan H. MacDonald

Appl. Phys. Lett. 78, 1550 (2001); http://dx.doi.org/10.1063/1.1355300 (3 pages) | Cited 57 times

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Mean-field-theory predicts that the Curie temperature Tc of a (III,Mn)V ferromagnet will be proportional to the valence band density-of-states of its host (III,V) semiconductor, suggesting a route toward room-temperature ferromagnetism in this materials class. In this letter, we use theoretical estimates of spin-wave energies and Monte Carlo simulations to demonstrate that long-wavelength collective fluctuations, neglected by mean-field theory, will limit the critical temperature in large density-of-states materials. We discuss implications for high Tc searches. © 2001 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Dd Nonmetallic ferromagnetic materials
75.40.Mg Numerical simulation studies
75.30.Ds Spin waves
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
71.20.Nr Semiconductor compounds
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Et Exchange and superexchange interactions

Photovoltaic effects on pinch-off voltage and open-circuit voltage in high-electron-mobility-transistor and Schottky-diode configurations

D. M. Kim

Appl. Phys. Lett. 78, 1553 (2001); http://dx.doi.org/10.1063/1.1355295 (3 pages)

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Photovoltaic effects on the pinch-off voltage (VP) in the high-electron-mobility-transistor (HEMT) and the open-circuit photovoltage (Vopt,OC) in the Schottky-diode configurations are characterized as a function of the optical input (Popt). The open-circuit photovoltage (Vopt,OC) in a Schottky-diode configuration, which has only a vertical field and every photogenerated excess minority carrier contributes to the photovoltage, can be described by Vopt,OC = nVth ln(Popt/Pref). However, the photovoltage (Vopt,FET ≡ ∣VP-VPO∣) in HEMT configuration, which has a lateral field as well as a vertical field to drift excess minority carriers to the source contact and results in reduced photovoltage development, can be modeled as Vopt,FET = V0(Popt/Prefo)γ. © 2001 American Institute of Physics.
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85.30.Tv Field effect devices
85.60.Bt Optoelectronic device characterization, design, and modeling
85.30.Kk Junction diodes
73.50.Pz Photoconduction and photovoltaic effects
85.30.De Semiconductor-device characterization, design, and modeling

Polarization-dependent discharge in fibers of a semiconducting ladder-type polymer

N. Kumar and K. S. Narayan

Appl. Phys. Lett. 78, 1556 (2001); http://dx.doi.org/10.1063/1.1354159 (3 pages) | Cited 4 times

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We report results on polarization-dependent photoinduced discharge in oriented fibers and films of ladder-type, electron-transporting polymer poly(benzimidazobenzophenanthroline). The photocarrier generation efficiency (ϕ) in the fiber, which is indicated by the rate of discharge, is found to be distinctly higher for light polarized parallel to the fiber axis (P∥) compared to the radially perpendicular direction (P⊥). Similar results, with ϕ anisotropy ∼ 10, are obtained for oriented films. These observations are different from previously obtained results on polyparaphenylenevinylene. The results are compared with polarization-dependent steady-state photoconductivity measurements. We interpret these results on the basis of molecular and macroscopic features of the material. © 2001 American Institute of Physics.
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72.40.+w Photoconduction and photovoltaic effects
61.41.+e Polymers, elastomers, and plastics
78.60.Fi Electroluminescence
73.61.Ph Polymers; organic compounds
73.50.Pz Photoconduction and photovoltaic effects
78.66.Qn Polymers; organic compounds

Photoluminescence modulation by high-frequency lateral electric fields in quantum wells

S. K. Zhang, P. V. Santos, and R. Hey

Appl. Phys. Lett. 78, 1559 (2001); http://dx.doi.org/10.1063/1.1355292 (3 pages) | Cited 3 times

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We investigate the modulation of the excitonic photoluminescence (PL) of GaAs quantum wells by high-frequency (frf) lateral electric fields. Under these fields, the PL becomes modulated in the form of pulses with repetition frequency of 2 frf. The periodic PL modulation is attributed to the time-dependent ionization of photogenerated excitons under the lateral electric field. The exciton ionization mechanism is proposed to be the impact ionization with electrons accelerated by the electric fields with a threshold field for ionization of about 15 V/cm. The different transport properties of electrons and holes are found to play a role in the exciton ionization process. © 2001 American Institute of Physics.
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78.67.De Quantum wells
73.21.Fg Quantum wells
78.20.Jq Electro-optical effects
78.55.Cr III-V semiconductors
73.63.Hs Quantum wells
73.50.Mx High-frequency effects; plasma effects
71.35.Gg Exciton-mediated interactions
78.47.-p Spectroscopy of solid state dynamics

On the origin of carrier localization in Ga1−xInxNyAs1−y/GaAs quantum wells

M.-A. Pinault and E. Tournié

Appl. Phys. Lett. 78, 1562 (2001); http://dx.doi.org/10.1063/1.1354153 (3 pages) | Cited 72 times

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We have investigated by temperature-dependent photoluminescence (PL) spectroscopy as-grown GaInNAs, InGaAs, and GaAsN quantum wells (QWs) embedded in a GaAs matrix. The evolution of the PL peak position and of the PL linewidth shows evidence of a strong carrier localization for the GaInNAs QWs only. The high delocalization temperature, in the 150 K range, indicates the presence of a high density of possibly deep-localizing potential wells. In addition, a higher density of nonradiative recombination centers appears to result in stronger carrier localization. Transmission electron microscopy reveals well defined, flat interfaces, in these comparatively high N-content (yN ∼ 0.04–0.05) QWs. Our results thus demonstrate that the origin of localization in GaInNAs QWs is the concomitant presence of both In and N, which may result in strain and/or composition fluctuations. © 2001 American Institute of Physics.
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73.21.Fg Quantum wells
68.65.Fg Quantum wells
78.67.De Quantum wells
78.55.Cr III-V semiconductors
73.20.Jc Delocalization processes

Large-scale local-density-approximation band gap-corrected GaAsN calculations

Lin-Wang Wang

Appl. Phys. Lett. 78, 1565 (2001); http://dx.doi.org/10.1063/1.1354162 (3 pages) | Cited 38 times

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The electronic structure of a GaAsN alloy is calculated using a 4096 atom supercell, with a 70 Ry plane wave basis cutoff and Ga atom 3d electrons as valence electrons. The charge density of this supercell is generated by patching the charge density of a small unit cell with the charge density of bulk GaAs. The local-density-approximation band gap error is corrected by modifying the nonlocal pseudopotentials. A localized nitrogen state [a1(N)] is obtained,and it plays an important role in the band gap reduction of GaAsN. © 2001 American Institute of Physics.
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71.20.Nr Semiconductor compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)

Auger recombination in long-wavelength infrared InNxSb1−x alloys

B. N. Murdin, M. Kamal-Saadi, A. Lindsay, E. P. O’Reilly, A. R. Adams, G. J. Nott, J. G. Crowder, C. R. Pidgeon, I. V. Bradley, J.-P. R. Wells, T. Burke, A. D. Johnson, and T. Ashley

Appl. Phys. Lett. 78, 1568 (2001); http://dx.doi.org/10.1063/1.1355301 (3 pages) | Cited 26 times

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Dilute nitrogen alloys of InSb exhibit strong band gap bowing with increasing nitrogen composition, shifting the absorption edge to longer wavelengths. The conduction band dispersion also has an enhanced nonparabolicity, which suppresses Auger recombination. We have measured Auger lifetimes in alloys with 11 and 15 μm absorption edges using a time-resolved pump-probe technique. We find the lifetimes to be longer at room temperature than equivalent band gap Hg1−yCdyTe alloys at the same quasi-Fermi level separation. The results are explained using a modified k⋅p Hamiltonian which explicitly includes interactions between the conduction band and a higher lying nitrogen-related resonant band. © 2001 American Institute of Physics.
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78.30.Fs III-V and II-VI semiconductors
78.47.-p Spectroscopy of solid state dynamics
71.20.Nr Semiconductor compounds

Hydrogen passivation and activation of oxygen complexes in silicon

S. N. Rashkeev, M. Di Ventra, and S. T. Pantelides

Appl. Phys. Lett. 78, 1571 (2001); http://dx.doi.org/10.1063/1.1355297 (3 pages) | Cited 10 times

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We report first-principles calculations in terms of which we describe the role of hydrogen in passivating or activating oxygen complexes in Si. In particular we find that attaching H to a pre-existing oxygen cluster can change the electric activity of the cluster. Furthermore, the addition of a hydrogen atom in the core structure of thermal donors can account for the NL10 electron-paramagnetic-resonance signal. The interaction of H with the thermal-donor-like defects at the Si–SiO2 is also discussed. © 2001 American Institute of Physics.
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71.55.Cn Elemental semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
76.30.Mi Color centers and other defects
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Band discontinuities in ZnMgSe/ZnCdSe(001) lattice-matched heterostructures

E. Pelucchi, S. Rubini, B. Bonanni, A. Franciosi, and M. Peressi

Appl. Phys. Lett. 78, 1574 (2001); http://dx.doi.org/10.1063/1.1350968 (3 pages) | Cited 2 times

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We present experimental and theoretical studies of lattice-matched interfaces between Zn1−yMgySe and Zn1−xCdxSe wide-band gap semiconductors. Ab initio pseudopotential calculations predict lattice matching for y/x∼1.6 and a valence band contribution to the band gap difference Qv decreasing gradually from 0.34 to 0.27 with increasing x and y. Experimental x-ray diffraction and photoemission spectroscopy results are mostly consistent with such predictions, although non-negligible deviations of the band offsets from commutativity were observed for selected alloy compositions. © 2001 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
79.60.Jv Interfaces; heterostructures; nanostructures
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)

n- and p-type dopants for cubic silicon nitride

Fumiyasu Oba, Kazuyoshi Tatsumi, Hirohiko Adachi, and Isao Tanaka

Appl. Phys. Lett. 78, 1577 (2001); http://dx.doi.org/10.1063/1.1354667 (3 pages) | Cited 8 times

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The formation and ionization energies of impurities in cubic silicon nitride are investigated through first-principles calculations. Among the elements in the groups III to VI, P and O are preferable for n-type doping, while Al is favorable for p-type doping in terms of the formation and ionization energies. The compensation of doped carriers associated with the incorporation of these impurities into anti and interstitial sites can be suppressed if appropriate growth conditions are chosen. © 2001 American Institute of Physics.
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61.72.up Other materials
71.15.Nc Total energy and cohesive energy calculations
71.55.Ht Other nonmetals
61.72.J- Point defects and defect clusters

SiGeC/Si superlattice microcoolers

Xiaofeng Fan, Gehong Zeng, Chris LaBounty, John E. Bowers, Edward Croke, Channing C. Ahn, Scott Huxtable, Arun Majumdar, and Ali Shakouri

Appl. Phys. Lett. 78, 1580 (2001); http://dx.doi.org/10.1063/1.1356455 (3 pages) | Cited 81 times

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Monolithically integrated active cooling is an attractive way for thermal management and temperature stabilization of microelectronic and optoelectronic devices. SiGeC can be lattice matched to Si and is a promising material for integrated coolers. SiGeC/Si superlattice structures were grown on Si substrates by molecular beam epitaxy. Thermal conductivity was measured by the 3ω method. SiGeC/Si superlattice microcoolers with dimensions as small as 40×40 μm2 were fabricated and characterized. Cooling by as much as 2.8 and 6.9 K was measured at 25 °C and 100 °C, respectively, corresponding to maximum spot cooling power densities on the order of 1000 W/cm2. © 2001 American Institute of Physics.
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07.20.-n Thermal instruments and apparatus
68.65.Cd Superlattices
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
85.80.Fi Thermoelectric devices
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
68.60.Dv Thermal stability; thermal effects
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.07.-b Nanoscale materials and structures: fabrication and characterization

Bipolarity in electrical conduction of transparent oxide semiconductor CuInO2 with delafossite structure

Hiroshi Yanagi, Tomomi Hase, Shuntaro Ibuki, Kazushige Ueda, and Hideo Hosono

Appl. Phys. Lett. 78, 1583 (2001); http://dx.doi.org/10.1063/1.1355673 (3 pages) | Cited 105 times

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A transparent oxide semiconductor with delafossite structure, CuInO2, was found to exhibit both p-type and n-type conduction by doping of an appropriate impurity and tuning of proper film-deposition conditions. Thin films of Ca-doped or Sn-doped CuInO2 (optical band gap = ∼ 3.9 eV) were prepared on α-Al2O3(001) single crystal substrates by pulsed laser deposition method. The films were deposited at 723 K in O2 atmosphere of 1.0 Pa for the Ca-doped films or 1.5 Pa for the Sn-doped films. The positive sign of the Seebeck coefficient demonstrated p-type conduction in the Ca-doped films, while the Seebeck coefficient of the Sn-doped films was negative indicating n-type conductivity. The electrical conductivities of Ca-doped and Sn-doped CuInO2 thin films were 2.8×10−3 S cm−1 and 3.8×10−3 S cm−1, respectively, at 300 K. © 2001 American Institute of Physics.
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73.61.Le Other inorganic semiconductors
73.50.Lw Thermoelectric effects
68.55.-a Thin film structure and morphology
81.15.Fg Pulsed laser ablation deposition
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Scanning Hall probe microscopy of flux penetration into a superconducting YBa2Cu3O7−δ thin film strip

A. N. Grigorenko, S. J. Bending, J. K. Gregory, and R. G. Humphreys

Appl. Phys. Lett. 78, 1586 (2001); http://dx.doi.org/10.1063/1.1352041 (3 pages) | Cited 9 times

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A high-resolution scanning Hall probe microscope has been used to measure flux profiles across one “wire” of a long YBa2Cu3O7−δ thin-film meander line as a function of both transport current density and applied magnetic field. Flux bundle penetration due to an applied current or magnetic field is demonstrated to occur at the same regions at the edge of the strip. A correlation between the surface topography of the meander line edges and the regions of penetration has been established. Penetrating flux profiles at low temperatures are in qualitative agreement with theories of dynamical instability of the order parameter. © 2001 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
68.35.B- Structure of clean surfaces (and surface reconstruction)
74.25.F- Transport properties

Patterning ferromagnetism in Ni80Fe20 films via Ga+ ion irradiation

W. M. Kaminsky, G. A. C. Jones, N. K. Patel, W. E. Booij, M. G. Blamire, S. M. Gardiner, Y. B. Xu, and J. A. C. Bland

Appl. Phys. Lett. 78, 1589 (2001); http://dx.doi.org/10.1063/1.1351519 (3 pages) | Cited 40 times

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We demonstrate that focused Ga+ ion irradiation can comprehensively modify the ferromagnetic properties of Ni80Fe20 thin films. Magneto-optic Kerr effect measurements at room temperature and magnetoresistance measurements at temperatures between 1.5 and 270 K characterized the irradiation effects. Irradiation steadily reduced the films’ room temperature coercivity, and a dose of 1.0×1016 ions/cm2 at 30 keV was found sufficient to cause a loss of ferromagnetism at room temperature in films of thickness up to 15.5 nm. In situ end-point detection and postirradiation atomic force microscopy confirmed that the sputtering which accompanied doses up to 1.0×1016 ions/cm2 did not compromise the protective caps on these Ni80Fe20 films. We therefore conclude that the modification of ferromagnetic properties occurred primarily because of direct Ga+ ion implantation. From these results, we speculate that focused Ga+ ion irradiation could be a convenient tool for the nanoscale patterning of magnetic properties in 3d transition metal thin films. © 2001 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Bb Fe and its alloys
61.80.Jh Ion radiation effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.82.Bg Metals and alloys
78.20.Ls Magneto-optical effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Array of nickel nanowires enveloped in polyaniline nanotubules and its magnetic behavior

Huaqiang Cao, Chenyang Tie, Zheng Xu, Jianming Hong, and Hai Sang

Appl. Phys. Lett. 78, 1592 (2001); http://dx.doi.org/10.1063/1.1354156 (3 pages) | Cited 27 times

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An array of nickel nanowires enveloped in polyaniline nanotubules was prepared by the “second-order-template” method. As the first step, an array of the polyaniline nanotubules was synthesized in the pores of an alumina membrane, then nickel nanowires were fabricated by electrochemical deposition of the nickel into the polyaniline nanotubules. The composite nanostructure was characterized by x-ray powder diffraction, and scanning electron micrography. Its magnetic properties were measured by a vibrating sample magnetometer. The coercivity and remanence are of high anisotropy with a maximum at θ=90° (parallel to the nanowires). © 2001 American Institute of Physics.
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81.07.Pr Organic-inorganic hybrid nanostructures
75.50.Tt Fine-particle systems; nanocrystalline materials
61.46.-w Structure of nanoscale materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.07.De Nanotubes
82.35.Np Nanoparticles in polymers
81.15.Pq Electrodeposition, electroplating
75.50.Cc Other ferromagnetic metals and alloys
75.30.Gw Magnetic anisotropy
81.05.Qk Reinforced polymers and polymer-based composites

Anomalous temperature dependence of coercivity and reversal mechanism in bulk-hardened rare earth-cobalt magnets

A. M. Gabay, W. Tang, Y. Zhang, and G. C. Hadjipanayis

Appl. Phys. Lett. 78, 1595 (2001); http://dx.doi.org/10.1063/1.1354670 (3 pages) | Cited 20 times

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The “anomalous” nonmonotonic temperature dependence of coercivity, reported in Sm–Zr–Co–Cu magnets, has also been observed in bulk-hardened Y–Zr–Co–Fe–Cu alloys with a similar microstructure. The phenomenon appears to be universal for all R–Co magnets (R=rare earth) having a microstructure consisting of R2Co17 cells surrounded by the RCo5 phase. The effect of R and Cu on the temperature dependence of coercivity cannot be simply explained by traditional domain-wall pinning model based on the difference in a domain wall energy. Possibility that the coercivity is controlled by nucleation of reversed domains in magnetically isolated R2Co17 cells is discussed. © 2001 American Institute of Physics.
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75.50.Vv High coercivity materials
75.60.Jk Magnetization reversal mechanisms
75.60.Ch Domain walls and domain structure

Enhanced metal–insulator transition and magnetoresistance in melt-processed La0.67Ca0.33MnO3 and Ho-doped manganites

A. K. Pradhan, B. K. Roul, Y. Feng, Y. Wu, S. Mohanty, D. R. Sahu, and P. Dutta

Appl. Phys. Lett. 78, 1598 (2001); http://dx.doi.org/10.1063/1.1354659 (3 pages) | Cited 15 times

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We report significant enhancement of magnetoresistance (MR) in melt-processed La0.67Ca0.33MnO3 (LCM) and in Ho-doped LCM samples. The LCM system exhibits surprising enhancement of metal–insulator transition (TIM) that coincides with the Curie transition temperature (Tc), TIM ≈ Tc, illustrating the enhanced percolative transport and spin-polarization through grain boundaries. Surprisingly, 1 mol % of addition of Ho enhances Tc of ∼ 70 K with remarkable colossal MR. The nanoscale Ho distribution is consistent with the magnetic inhomogeneity-induced MR due to phase segregation in Ho-doped sample whereas charge-segregation picture is valid for undoped LCM. © 2001 American Institute of Physics.
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75.47.Gk Colossal magnetoresistance
72.60.+g Mixed conductivity and conductivity transitions
75.50.Dd Nonmetallic ferromagnetic materials
72.25.Ba Spin polarized transport in metals
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.72.Mm Grain and twin boundaries
64.75.-g Phase equilibria
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.40.Rs Electrical and magnetic properties related to treatment conditions

Ballistic electron microscopy study of ultrathin oxidized aluminum barriers for magnetic tunnel junctions

W. H. Rippard, A. C. Perrella, and R. A. Buhrman

Appl. Phys. Lett. 78, 1601 (2001); http://dx.doi.org/10.1063/1.1352045 (3 pages) | Cited 19 times

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Ballistic electron emission microscopy has been used to study thin aluminum oxide tunnel junction barriers formed both by magnetron sputter deposition and thermal evaporation. We have found that the barriers made by oxidation of evaporated Al become fully formed at a significantly thinner mean deposited thickness (∼6 Å) than junctions made by sputter deposition. The effective barrier height of the aluminum oxide has been determined to be 1.22±0.05 eV and is independent of the method of deposition, thickness, and oxidation conditions. © 2001 American Institute of Physics.
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68.37.Vj Field emission and field-ion microscopy
81.15.Cd Deposition by sputtering
73.40.Gk Tunneling
81.65.Mq Oxidation
68.55.-a Thin film structure and morphology
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Crystalline zirconia oxide on silicon as alternative gate dielectrics

S. J. Wang, C. K. Ong, S. Y. Xu, P. Chen, W. C. Tjiu, J. W. Chai, A. C. H. Huan, W. J. Yoo, J. S. Lim, W. Feng, and W. K. Choi

Appl. Phys. Lett. 78, 1604 (2001); http://dx.doi.org/10.1063/1.1354161 (3 pages) | Cited 42 times

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Epitaxial crystalline yittria-stabilized zirconia (YSZ) oxide films were grown on silicon wafers by the laser molecular beam epitaxy technique. The interface of crystalline YSZ film in contact with silicon was found to be atomically sharp and commensurately crystallized without an amorphous layer. An x-ray photoelectron spectroscopy depth profile and transmission electron microscopy investigation showed that no SiO2 formed at the interface. For a film with electrical equivalent oxide thickness (teox) 14.6 Å, the leakage current is about 1.1×10−3 A/cm2 at 1 V bias voltage. The hysteresis and interface state density in this film are measured to be less than 10 mV and 2.0×1011 eV−1 cm−2, respectively. © 2001 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.Ct Interface structure and roughness
73.20.At Surface states, band structure, electron density of states
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Formation of a stratified lanthanum silicate dielectric by reaction with Si(001)

M. Copel, E. Cartier, and F. M. Ross

Appl. Phys. Lett. 78, 1607 (2001); http://dx.doi.org/10.1063/1.1355002 (3 pages) | Cited 109 times

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We have characterized the structure and electrical properties of lanthanum silicate layers formed on Si(001) by reaction of lanthanum oxide with the substrate. Postoxidation of the deposited films results in the formation of a stacked dielectric with a lanthanum silicate layer atop an interfacial layer of SiO2. This structure combines the interfacial properties of SiO2 with the large permittivity of lanthanum silicate. Although the resulting film has leakage properties far superior to an equivalent thickness of SiO2, there is evidence of significant quantities of ionic charge that must be eliminated before use in electronic applications. © 2001 American Institute of Physics.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
68.35.Fx Diffusion; interface formation
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.65.Mq Oxidation
79.60.Jv Interfaces; heterostructures; nanostructures
68.37.Xy Scanning Auger microscopy, photoelectron microscopy
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
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Production and measurements of individual single-wall nanotubes and small ropes of carbon

Sivaram Arepalli, Pavel Nikolaev, William Holmes, and Bradley S. Files

Appl. Phys. Lett. 78, 1610 (2001); http://dx.doi.org/10.1063/1.1352659 (3 pages) | Cited 13 times

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This work focuses on the size and spatial dependence of single-wall carbon nanotubes produced by the pulsed-laser vaporization technique. The study indicates that very long (tens of microns) individual nanotubes form in the vicinity of the target, and subsequently coalesce into bundles. The role of the inner flow tube is confirmed to restrict plume expansion and improve interactions between carbon atoms resulting in nanotube and rope formation. The effect of the flowing buffer gas seems to influence the dispersion of particulate contaminant material in the nanotube product. More particulate matter is produced at lower oven temperatures. © 2001 American Institute of Physics.
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81.07.De Nanotubes
61.46.-w Structure of nanoscale materials
81.16.Mk Laser-assisted deposition
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