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6 Dec 2004

Volume 85, Issue 23, pp. 5499-5791

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 5694 (2004); http://dx.doi.org/10.1063/1.1828575 (3 pages)

M. Y. Shen, C. H. Crouch, J. E. Carey, and E. Mazur
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Detection of subnanometric layer at the Si∕SiO2 interface and related strain measurements

P. Donnadieu, E. Blanquet, N. Jakse, and P. Mur

Appl. Phys. Lett. 85, 5574 (2004); http://dx.doi.org/10.1063/1.1831561 (3 pages) | Cited 2 times

Online Publication Date: 8 December 2004

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The structure of the Si∕SiO2 interface was investigated by high-resolution transmission electron microscopy (HRTEM) and electron diffraction, which appears as an efficient tool to detect any organized layer at the interface. Using HRTEM image analysis, a 1‐nm-thick distorted Si layer is identified at the interface, the local deformation corresponds to a compressive stress of approximately 2 GPa.
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81.05.Cy Elemental semiconductors
68.35.Ct Interface structure and roughness
68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
68.37.Lp Transmission electron microscopy (TEM)
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Influence of defects on the kinetic of C49–C54 TiSi2 transformation

F. La Via, F. Mammoliti, and M. G. Grimaldi

Appl. Phys. Lett. 85, 5577 (2004); http://dx.doi.org/10.1063/1.1831559 (3 pages)

Online Publication Date: 8 December 2004

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TiSi2 C49 thin films with different concentrations of defects have been prepared by conventional annealing, in the 460–540 °C temperature range, of a Ti films deposited on a polycrystalline Si layer. The residual sheet resistance of the C49 films decreased with increasing both the annealing temperature and the annealing duration indicating the occurrence of defect annealing at higher temperature and∕or longer times. A successive annealing at 650 °C was used to promote the C49–C54 transition and the transformation rate was measured by in situ sheet resistance measurements. The C49–C54 transition time decreased with the residual sheet resistance of the C49 phase. The activation energy for the transformation increased from 3.09±0.75 to 6.12±0.96 eV with increasing the defect concentration in the C49 phase. This strong dependence can explain the large variation of the kinetic results reported in the literature.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.40.Gh Other heat and thermomechanical treatments
64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder

Density profiles and electrical properties of thermally grown oxide nanofilms on p-type 6H–SiC(0001)

S. Hazra, S. Chakraborty, and P. T. Lai

Appl. Phys. Lett. 85, 5580 (2004); http://dx.doi.org/10.1063/1.1829385 (3 pages) | Cited 5 times

Online Publication Date: 8 December 2004

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Thermally grown silicon oxide films on p-type 6H–silicon carbide substrate under different oxidation and nitridation conditions have been characterized by x-ray reflectivity technique. An electron density profile obtained from the analysis of the x-ray reflectivity data shows that the thickness, density of the oxide film, and structure of the oxide-SiC interface strongly depend on the different growth conditions. In particular, the density of the oxide film for all samples other than that grown in NO is found to be much lower and also not fixed within. It is maximum at the interface and gradually decreases toward the top in all samples except for the sample grown in O2 followed by NO nitridation. For the latter, a very low density at the interface region has been observed. The sample grown in NO shows the best performance in capacitance–voltage characteristic and reliability studies suggesting that the bad performance of the oxide grown on the p-type SiC system as metal–oxide–semiconductor devices, is mainly linked to the low-density oxide film and can be overcome under proper growth condition.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
84.32.Tt Capacitors
73.63.Bd Nanocrystalline materials
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
81.65.Mq Oxidation

Suppression of thermal atomic interdiffusion in C-doped InGaAs∕AlGaAs quantum well laser structures using TiO2 dielectric layers

P. L. Gareso, M. Buda, L. Fu, H. H. Tan, and C. Jagadish

Appl. Phys. Lett. 85, 5583 (2004); http://dx.doi.org/10.1063/1.1833563 (3 pages) | Cited 9 times

Online Publication Date: 8 December 2004

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The effects of thermal annealing on C-doped InGaAs∕AlGaAs quantum well laser structures capped with titanium dioxide (TiO2) layers were investigated. The atomic interdiffusion was greatly suppressed by the presence of a TiO2 capping layer during annealing, inhibiting even the thermal intermixing observed in the uncapped sample. An increase in the amount of lattice contraction associated with the presence of substitutional carbon CAs after annealing without a capping layer was observed, but not after annealing with a TiO2 capping layer. Capacitance–voltage measurements confirmed the electrical activation of carbon after annealing without a dielectric layer and show a negligible change after annealing using a TiO2 capping layer. The possible mechanisms involving both the atomic intermixing on the group III sublattice and carbon activation on the group V sublattice and the implications for optoelectronic device integration using impurity-free intermixing are discussed.
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81.05.Ea III-V semiconductors
81.07.St Quantum wells
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
68.35.Fx Diffusion; interface formation
73.63.Hs Quantum wells
78.67.De Quantum wells
78.55.Cr III-V semiconductors
81.40.Gh Other heat and thermomechanical treatments
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
42.55.Px Semiconductor lasers; laser diodes
61.72.S- Impurities in crystals
77.55.-g Dielectric thin films

Reduced defect densities in the ZnO epilayer grown on Si substrates by laser-assisted molecular-beam epitaxy using a ZnS epitaxial buffer layer

T. Onuma, S. F. Chichibu, A. Uedono, Y.-Z. Yoo, T. Chikyow, T. Sota, M. Kawasaki, and H. Koinuma

Appl. Phys. Lett. 85, 5586 (2004); http://dx.doi.org/10.1063/1.1832734 (3 pages) | Cited 17 times

Online Publication Date: 8 December 2004

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Nonradiative photoluminescence (PL) lifetime (τnr) and point defect density in the (0001) ZnO epilayer grown on (111) Si substrates by laser-assisted molecular-beam epitaxy (L-MBE) using a (0001) ZnS epitaxial buffer layer were compared with those in the ZnO films on (111) and (001) Si substrates prepared by direct transformation of ZnS epilayers on Si by thermal oxidation [Yoo et al., Appl. Phys. Lett. 78, 616 (2001)]. Both the ZnO films exhibited excitonic reflectance anomalies and corresponding PL peaks at low temperature, and the density or size of vacancy-type point defects (Zn vacancies), which were measured by the monoenergetic positron annihilation measurement, in the L-MBE epilayer was lower than that in the films prepared by the oxidation transformation. The ZnO epilayer grown on a (0001) ZnS epitaxial buffer on (111) Si exhibited longer τnr of 105 ps at room temperature.
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81.05.Dz II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.J- Point defects and defect clusters
78.55.Et II-VI semiconductors
68.55.A- Nucleation and growth
78.66.Hf II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Effect of Bi surfactant on atomic ordering of GaAsSb

W. Y. Jiang, J. Q. Liu, M. G. So, T. S. Rao, M. Thewalt, K. L. Kavanagh, and S. P. Watkins

Appl. Phys. Lett. 85, 5589 (2004); http://dx.doi.org/10.1063/1.1830687 (3 pages) | Cited 2 times

Online Publication Date: 8 December 2004

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The addition of small quantities of a Bi surfactant is shown to have dramatic effects on the microstructure of GaAsSb alloys grown by organometallic vapor phase epitaxy (OMVPE). Epilayers grown without Bi show weak atomic ordering in plan-view selective area electron diffraction measurements, with periodicity of three or six times the [110] lattice spacing as previously reported. The addition of Bi at a ratio of 1% Bi∕Ga to the gas flow results in the appearance of strong CuAu and chalcopyrite ordering, as determined from electron diffraction measurements in both undoped, and heavily carbon doped layers. High-resolution, transmission electron microscopy lattice images clearly show the coexistence of {100}, {210} ordered and disordered structures with domain sizes of ∼10–20 nm. Photoluminescence shows no band gap changes in GaAsSb samples with and without {100} and {210} ordering.
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68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
68.37.Lp Transmission electron microscopy (TEM)

Tunable optical switch using magnetic fluids

H. E. Horng, C. S. Chen, K. L. Fang, S. Y. Yang, J. J. Chieh, Chin-Yih Hong, and H. C. Yang

Appl. Phys. Lett. 85, 5592 (2004); http://dx.doi.org/10.1063/1.1833564 (3 pages) | Cited 37 times

Online Publication Date: 8 December 2004

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With a tunable refractive index, magnetic fluid can be applied to the development of adjustable optical devices. In this work, a magnetic-fluid-based optical switch is designed and characterized. The optical switch is formed by sealing magnetic fluid between two glass prisms. When a light is incident to one side of one of the prisms, a reflected light from the magnetic fluid film comes out from the same prism, whereas a transmitted light through the film emits from the other prism. It was found that the intensity ratio of the reflected light to the transmitted light can be manipulated by varying the external magnetic field strength. This implies that the light intensity can be switched between two paths. The switching efficiency also depends on the incident angle of a light into the prism. We then theoretically derive the incident-angle dependent switching efficiency to clarify relevant physical mechanisms.
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42.79.Bh Lenses, prisms and mirrors
42.65.Pc Optical bistability, multistability, and switching, including local field effects
75.50.Mm Magnetic liquids
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.15.+e Liquid thin films

Strong light scattering in macroporous TiO2 monoliths induced by phase separation

Koji Fujita, Junko Konishi, Kazuki Nakanishi, and Kazuyuki Hirao

Appl. Phys. Lett. 85, 5595 (2004); http://dx.doi.org/10.1063/1.1823596 (3 pages) | Cited 10 times

Online Publication Date: 8 December 2004

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Macroporous titania (TiO2) monoliths have been prepared from systems containing titania colloid and poly(ethylene oxide) using a sol-gel method, and the light-scattering properties have been investigated by means of coherent backscattering. Three-dimensionally interconnected macroporous morphology is obtained by inducing the phase separation parallel to the sol-gel transition. The crystal structure of TiO2 gel is transformed from anatase to rutile through the heat treatment above 900 °C, while the macroporous morphology remains unchanged. We show that the rutile-type TiO2-based macropurous monoliths are strongly scattering media for visible light.
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81.05.Rm Porous materials; granular materials
64.75.-g Phase equilibria
78.35.+c Brillouin and Rayleigh scattering; other light scattering
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.35.B- Structure of clean surfaces (and surface reconstruction)
64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
81.40.Gh Other heat and thermomechanical treatments
61.50.Ks Crystallographic aspects of phase transformations; pressure effects
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Dimensional structural transition in CdTe∕CdxZn1−xTe nanostructures

H. S. Lee, H. L. Park, and T. W. Kim

Appl. Phys. Lett. 85, 5598 (2004); http://dx.doi.org/10.1063/1.1832749 (3 pages) | Cited 11 times

Online Publication Date: 8 December 2004

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CdTe nanostructures were grown on CdxZn1−xTe buffer layers by using molecular-beam epitaxy and atomic-layer epitaxy. The atomic force microscopy image showed that uniform CdTe quantum dots were formed on ZnTe buffer layer. Photoluminescence measurements showed that the excitonic peak corresponding to the interband transitions from the ground electronic subband to the ground heavy-hole band in the CdTe∕CdxZn1−xTe nanostructure shifted to a higher energy with increasing Cd mole fraction. The activation energy of the electrons confined in the CdTe∕ZnTe quantum dots was higher than those of electrons in CdTe∕CdxZn1−xTe nanostructures. These results can help improve understanding of the dimensional structural transition in CdTe∕CdxZn1−xTe nanostructures.
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81.05.Dz II-VI semiconductors
81.07.Bc Nanocrystalline materials
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.37.Ps Atomic force microscopy (AFM)
78.55.Et II-VI semiconductors

“Hidden hydrogen” in as-grown ZnO

G. Alvin Shi, Marjan Saboktakin, Michael Stavola, and S. J. Pearton

Appl. Phys. Lett. 85, 5601 (2004); http://dx.doi.org/10.1063/1.1832736 (3 pages) | Cited 43 times

Online Publication Date: 8 December 2004

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An O–H stretching line at 3326.3 cm−1 was previously assigned to a shallow donor that is introduced into ZnO by H. This infrared line has been found to appear in as-grown ZnO samples when they are annealed near 400 °C without an external source of H, showing that there is an H-containing defect in commercially available ZnO that is not seen by infrared spectroscopy that can be converted into a shallow donor. The interstitial H2 molecule in ZnO is suggested as a candidate for the “hidden” H species.
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81.05.Dz II-VI semiconductors
61.72.J- Point defects and defect clusters
61.72.S- Impurities in crystals
78.40.Fy Semiconductors
61.72.Cc Kinetics of defect formation and annealing
78.30.Fs III-V and II-VI semiconductors
81.40.Gh Other heat and thermomechanical treatments

Thermally stimulated current in self-organized InAs quantum dots

J. C. Fan, Y. C. Wang, I. S. Chen, K. J. Hsiao, and Y. F. Chen

Appl. Phys. Lett. 85, 5604 (2004); http://dx.doi.org/10.1063/1.1832760 (3 pages) | Cited 1 time

Online Publication Date: 8 December 2004

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We have measured the thermally stimulated current from self-organized InAs quantum dots grown by molecular-beam epitaxy. The glow curve exhibits peaks at 43, 82, and 127 K with accompanying attenuated current oscillations at 107 K. Based on the excitation energy above and below the GaAs band gap, the oscillations are ascribed to AsGa-related point defects in the conduction GaAs matrix. By comparing with the photoluminescence and photoconductivity measurements, we conclude that the peaks at 82 and 43 K arise from the electron trapping in the InAs quantum dots. We point out that the technique of thermally stimulated current provides a simple alternative method to obtain the energy levels in self-organized quantum-dot systems.
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72.20.Pa Thermoelectric and thermomagnetic effects
68.65.Hb Quantum dots (patterned in quantum wells)
78.55.Cr III-V semiconductors
73.63.Kv Quantum dots
78.67.Hc Quantum dots
71.20.Nr Semiconductor compounds
61.72.J- Point defects and defect clusters
73.50.Pz Photoconduction and photovoltaic effects
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Effect of band offset on the open circuit voltage of heterojunction CuIn1−xGaxSe2 solar cells

Akimasa Yamada, Koji Matsubara, Keiichiro Sakurai, Shogo Ishizuka, Hitoshi Tampo, Paul J. Fons, Kakuya Iwata, and Shigeru Niki

Appl. Phys. Lett. 85, 5607 (2004); http://dx.doi.org/10.1063/1.1831566 (3 pages) | Cited 12 times

Online Publication Date: 8 December 2004

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The reasons behind why the theoretically estimated open circuit voltage (Voc) of CuIn1−xGaxSe2 solar cells with large x values has not been realized are discussed. Typically, the reduction in Voc is estimated only on the basis of the conduction-band offset between the absorber and the window material. The importance of the electron affinity difference between the window and the transparent electrode must also be taken into account. Based upon both of these factors, a material selection guideline is reported for the window and the transparent electrode layers suitable for high-x CuIn1−xGaxSe2 absorber-based solar cells.
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84.60.Jt Photoelectric conversion
71.20.Nr Semiconductor compounds
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Electronic charge effects on dislocation cores in silicon

M. M. de Araújo, J. F. Justo, and R. W. Nunes

Appl. Phys. Lett. 85, 5610 (2004); http://dx.doi.org/10.1063/1.1830073 (3 pages) | Cited 3 times

Online Publication Date: 8 December 2004

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Using first-principles calculations, we investigate electronic charge effects on the structural stability of partial dislocations in silicon. For the 30° partial dislocation, we find that the unreconstructed core sustains all possible charge states associated with the dislocation-related electronic bands, as the Fermi level (μe) sweeps the electronic band gap, while the reconstructed core remains neutral for p-type doping and intrinsic regimes. Both core configurations become negatively charged for n-type doping. In the case of the 90° partial dislocation, the three known core configurations (namely, the single-period and double-period reconstructed cores and the unreconstructed one) remain neutral in the p-type and intrinsic regimes, but the negatively charged states become stable in the n-type region, for all three geometries. More important, we find that the relative stability between the three structures is strongly charge-state dependent, with the unreconstructed core becoming energetically favorable in the n-type regime. Our results provide elements for understanding the role of doping on dislocation mobility in semiconductors.
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61.72.Bb Theories and models of crystal defects
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
71.55.Cn Elemental semiconductors
71.20.Mq Elemental semiconductors
61.72.S- Impurities in crystals
73.20.At Surface states, band structure, electron density of states

Al–Si multilayers: A synthetic material with large thermoelectric anisotropy

A. Kyarad and H. Lengfellner

Appl. Phys. Lett. 85, 5613 (2004); http://dx.doi.org/10.1063/1.1830680 (3 pages) | Cited 6 times

Online Publication Date: 8 December 2004

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A synthetic material with large thermoelectric anisotropy has been prepared from a metal–semiconductor multilayer structure. By an alloying process, a multilayer stack A–B–A…, where A and B are pure aluminum and n-silicon, is produced with a thermoelectric anisotropy ΔS=S∥−S⊥≅1.5 mV∕K, where S∥ and S⊥ are the absolute Seebeck coefficients along and perpendicular to the layers, respectively. The use of this synthetic material for light sensing applications is demonstrated.
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72.15.Jf Thermoelectric and thermomagnetic effects
72.20.Pa Thermoelectric and thermomagnetic effects
73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential

Conductivity and Hall effect of free-standing highly resistive epitaxial GaN:Fe substrates

P. Kordoš, M. Morvic, J. Betko, J. Novák, J. Flynn, and G. R. Brandes

Appl. Phys. Lett. 85, 5616 (2004); http://dx.doi.org/10.1063/1.1831568 (3 pages) | Cited 3 times

Online Publication Date: 8 December 2004

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Free-standing highly resistive Fe-doped GaN layers grown by hydride vapor phase epitaxy were characterized by temperature-dependent conductivity and Hall effect measurements. Samples with a room-temperature resistivity of 1.6×107–6×108 Ω cm and a Hall mobility of ∼330 cm2 V−1 s−1 showed simple band conduction with the mobility power x=−1.5 and an activation energy 0.58–0.60 eV, which can be attributed to a Fe acceptor. Samples with a lower mobility, ⩽10 cm2 V−1 s−1, exhibited an increase of the mobility with temperature. Here, the conduction seems to be strongly influenced by potential barriers at inhomogeneities, with an activation energy of 0.21 eV and a barrier height of 0.14–0.18 eV. The activation energy 0.36 and 0.40 eV, evaluated from the resistivity measurements, does not correspond to that of the Fe acceptor.
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81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Kk Vapor phase epitaxy; growth from vapor phase
73.61.Ey III-V semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
72.80.Ey III-V and II-VI semiconductors
71.55.Eq III-V semiconductors
61.72.S- Impurities in crystals

Strain modulation of transport criticality in RuO2-based thick-film resistors

Sonia Vionnet-Menot, Claudio Grimaldi, Peter Ryser, Thomas Maeder, and Sigfrid Strässler

Appl. Phys. Lett. 85, 5619 (2004); http://dx.doi.org/10.1063/1.1835996 (3 pages) | Cited 1 time

Online Publication Date: 8 December 2004

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We show that in RuO2–glass composites the nonuniversal resistivity exponent can be modulated by an applied mechanical strain, signaled by a logarithmic divergence of the piezoresistive response at the percolation threshold. We interpret this phenomenon as being due to a tunneling-distance dependence of the transport exponent, supporting therefore a theory of transport nonuniversality proposed some years ago.
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84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)
73.40.Gk Tunneling
72.80.Tm Composite materials

Pinning a domain wall in (Ga,Mn)As with focused ion beam lithography

A. W. Holleitner, H. Knotz, R. C. Myers, A. C. Gossard, and D. D. Awschalom

Appl. Phys. Lett. 85, 5622 (2004); http://dx.doi.org/10.1063/1.1829797 (3 pages) | Cited 4 times

Online Publication Date: 8 December 2004

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We utilize a focused beam of Ga+ ions to define magnetization pinning sites in a ferromagnetic epilayer of (Ga,Mn)As. The nonmagnetic defects locally increase the magnetocrystalline anisotropy energies, by which a domain wall is pinned at a given position. We demonstrate techniques for manipulating domain walls at these pinning sites as probed with the giant planar Hall effect. By varying the magnetic field angle relative to the crystal axes, an upper limit is placed on the local effective anisotropy energy.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.70.Ak Magnetic properties of monolayers and thin films
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
81.16.Nd Micro- and nanolithography
68.55.-a Thin film structure and morphology

Linear collapse of the depolarization shift in very dilute two-dimensional hole gases

A. S. Plaut, A. Pinczuk, B. S. Dennis, C. F. Hirjibehedin, L. N. Pfeiffer, and K. W. West

Appl. Phys. Lett. 85, 5625 (2004); http://dx.doi.org/10.1063/1.1833562 (3 pages)

Online Publication Date: 8 December 2004

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Very dilute two-dimensional hole systems were probed by resonant inelastic light scattering. This extremely high mobility system occurs in AlxGa1−xAs∕GaAs quantum wells designed specifically for their light insensitivity. We find that the depolarization shift in intersubband transitions decreases linearly for hole densities below p=6.6×1010 cm−2, dropping to zero below p=1×1010 cm−2.
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78.67.De Quantum wells
73.21.Fg Quantum wells
78.55.Cr III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance

Hydrogen-doped high conductivity ZnO films deposited by radio-frequency magnetron sputtering

Liang-Yih Chen, Wen-Hwa Chen, Jia-Jun Wang, Franklin Chau-Nan Hong, and Yan-Kuin Su

Appl. Phys. Lett. 85, 5628 (2004); http://dx.doi.org/10.1063/1.1835991 (3 pages) | Cited 47 times

Online Publication Date: 8 December 2004

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Hydrogen-doped zinc oxide (ZnO:H) films were deposited by rf magnetron sputtering as transparent conductive films. The resistivity of ZnO:H film was significantly reduced by the addition of H2 in Ar during rf sputtering. The electrical resistivity of ZnO:H films reached 2×10−4 Ω cm. The carrier concentration increased with increasing H2 concentration during deposition. X-ray diffraction results showed that the d0002 interplanar spacing increased with increasing H2 concentrations. The carrier concentration was significantly reduced in two orders of magnitude by increasing the substrate temperature from 150 to 250 °C during deposition. Both results suggested that the increase of carrier concentration by adding H2 during sputtering was due to the hydrogen donor rather than the oxygen vacancies in ZnO films, consistent with the theoretical predictions by Van de Walle. UV–visible spectroscopy further showed that the transmittance is high up to 100% in the visible range. The band gap determined by optical absorption increased with increasing H2 composition. The phenomenon is interpreted as the filling of conduction band by electrons in n-type semiconductor.
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68.55.-a Thin film structure and morphology
73.61.Ga II-VI semiconductors
78.66.Hf II-VI semiconductors
78.40.Fy Semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
61.72.J- Point defects and defect clusters
81.15.Cd Deposition by sputtering

Enhanced photoluminescence from GaAsSb quantum wells

Alan R. Kost, Xiaolan Sun, Nasser Peyghambarian, Nayer Eradat, Espen Selvig, Bjorn-Ove Fimland, and David H. Chow

Appl. Phys. Lett. 85, 5631 (2004); http://dx.doi.org/10.1063/1.1759381 (3 pages) | Cited 1 time

Online Publication Date: 8 December 2004

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We describe promising semiconductor materials for optoelectronics. GaAsSb/AlSb quantum wells on GaSb substrates show photoluminescence near 1.54 μm (0.8 eV) that increases with increasing arsenic fraction. The materials can be monolithically integrated with AlGaSb/AlSb or AlGaAsSb/AlAsSb Bragg mirrors. © 2004 American Institute of Physics.
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81.07.St Quantum wells
78.67.De Quantum wells
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
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Low-current spin-transfer switching and its thermal durability in a low-saturation-magnetization nanomagnet

K. Yagami, A. A. Tulapurkar, A. Fukushima, and Y. Suzuki

Appl. Phys. Lett. 85, 5634 (2004); http://dx.doi.org/10.1063/1.1829140 (3 pages) | Cited 74 times

Online Publication Date: 8 December 2004

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A spin-transfer magnetization switching technique is a promising candidate as a writing mechanism for a high-density magnetic random access memory because of its scalability. The required switching current Ic, however, is still too large for this technique to be applied to MRAM using tunneling magnetoresistive devices. Here, it is demonstrated that reducing the saturation magnetization Ms of magnet cells is an effective way to decrease Ic. Use of a CoFeB film with μ0Ms of 0.75 T as a magnet cell reduced Ic measured with a continuous current by an order of magnitude. We changed the duration of a writing current pulse from 1 μs to 5 s to investigate thermal effects on the switching process, and predicted that CoFeB magnet cells with low Ic can be compatible with the thermal durability required for MRAM applications.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.50.Bb Fe and its alloys
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Sg Magnetocaloric effect, magnetic cooling
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.47.De Giant magnetoresistance

Head-to-head domain-wall phase diagram in mesoscopic ring magnets

M. Kläui, C. A. F. Vaz, J. A. C. Bland, L. J. Heyderman, F. Nolting, A. Pavlovska, E. Bauer, S. Cherifi, S. Heun, and A. Locatelli

Appl. Phys. Lett. 85, 5637 (2004); http://dx.doi.org/10.1063/1.1829800 (3 pages) | Cited 60 times

Online Publication Date: 8 December 2004

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The nanoscale spin structure of head-to-head domain walls in mesoscopic ferromagnetic rings has been studied by high-resolution nonintrusive photoemission electron microscopy as a function of both ring width (100–730 nm) and film thickness (2–38 nm). Depending on the geometry, two types of head-to-head domain walls are found (vortex and transverse walls). The experimental phase diagram, which identifies the transition between the wall types, is compared to analytical calculations of the energy and micromagnetic simulations, which are found to agree well with the experimental results.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
75.60.Ch Domain walls and domain structure
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
79.60.-i Photoemission and photoelectron spectra

Thin films of SmCo5 with very high perpendicular magnetic anisotropy

J. Sayama, K. Mizutani, T. Asahi, and T. Osaka

Appl. Phys. Lett. 85, 5640 (2004); http://dx.doi.org/10.1063/1.1829792 (3 pages) | Cited 27 times

Online Publication Date: 8 December 2004

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Thin films of SmCo5 with extraordinarily high perpendicular magnetic anisotropy were prepared by introducing a Cu∕Ti dual underlayer and controlling the substrate temperature during the sputter deposition. Under optimized conditions, the magnetic anisotropy constant reached 4.0×107 erg∕cm3, and the coercivity and the remanence ratio in the direction perpendicular to the film surface were 12.0 kOe and unity, respectively. The high perpendicular magnetic anisotropy is attributed to the high degree of preferred orientation of the c axis; the full width at half maximum in the rocking curve of SmCo5(002) reflection was 3.1°.
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81.05.Bx Metals, semimetals, and alloys
75.50.Cc Other ferromagnetic metals and alloys
75.30.Gw Magnetic anisotropy
75.50.Vv High coercivity materials
75.70.Ak Magnetic properties of monolayers and thin films
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.15.Cd Deposition by sputtering

Magnetic-field-controllable avalanche breakdown and giant magnetoresistive effects in Gold∕semi-insulating-GaAs Schottky diode

Z. G. Sun, M. Mizuguchi, T. Manago, and H. Akinaga

Appl. Phys. Lett. 85, 5643 (2004); http://dx.doi.org/10.1063/1.1834733 (3 pages) | Cited 24 times

Online Publication Date: 8 December 2004

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Gold (Au)∕semi-insulating (SI)-GaAs Schottky diode was fabricated by the standard photolithography method using wet etching. Magnetic-field-dependent avalanche breakdown phenomena were observed in the current–voltage curves measured under magnetic field. The avalanche breakdown due to impact ionization was postponed to higher electrical field under applied magnetic field. Accordingly, threshold voltages of avalanche breakdown increased with the applied magnetic field. Above 0.2 T, avalanche breakdown was totally quenched. When Au‐SI‐GaAs Schottky diode was operated above the threshold voltage, giant mangetoresistive effects up to 100 000% were achieved under magnetic field of 0.8 T.
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85.30.Kk Junction diodes
85.30.Hi Surface barrier, boundary, and point contact devices
75.47.De Giant magnetoresistance
73.40.Ns Metal-nonmetal contacts
72.20.Ht High-field and nonlinear effects

Comparison of ac susceptibility of YBa2Cu3O7 coated conductors and single crystals

D.-X. Chen, E. Pardo, A. Sanchez, A. Palau, T. Puig, and X. Obradors

Appl. Phys. Lett. 85, 5646 (2004); http://dx.doi.org/10.1063/1.1833568 (3 pages) | Cited 13 times

Online Publication Date: 8 December 2004

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The complex ac susceptibility of YBa2Cu3O7 (YBCO) coated conductor and YBCO single crystal has been measured at 77 K as a function of field amplitude and frequency, from which the E(J) characteristic is deduced. It is shown that the E(J) in the single crystal obeys a power law in a large range above Ec=1 μV∕cm, indicating a flux creep mechanism, whereas for the coated conductor there appears a transition from flux creep to flux flow at E∼10Ec. The reported contactless technique may be conveniently used for the research and development of coated conductors.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
74.70.Dd Ternary, quaternary, and multinary compounds (including Chevrel phases, borocarbides, etc.)
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.F- Transport properties
74.20.-z Theories and models of superconducting state
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