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24 Nov 2008

Volume 93, Issue 21, Articles (21xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 93, 214101 (2008); http://dx.doi.org/10.1063/1.3025819 (3 pages)

Brian Abbey, Garth J. Williams, Mark A. Pfeifer, Jesse N. Clark, Corey T. Putkunz, Angela Torrance, Ian McNulty, T. M. Levin, Andrew G. Peele, and Keith A Nugent
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Carrier concentration dependence of terahertz transmission on conducting ZnO films

Guohong Ma, Dong Li, Hong Ma, Jie Shen, Chenguo Wu, Jin Ge, Shuhong Hu, and Ning Dai

Appl. Phys. Lett. 93, 211101 (2008); http://dx.doi.org/10.1063/1.3036708 (3 pages) | Cited 7 times

Online Publication Date: 24 November 2008

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With the dc reactive magnetron sputtering method, conducting ZnO thin films with different carrier concentrations on glass substrate were fabricated. The dielectric responses of the ZnO films are characterized with terahertz time-domain spectroscopy. Frequency-dependent conductivity, power absorption, and refractive index are obtained, and the experimental results can be well reproduced with the classic Drude model. Our results reveal that by adjusting the carrier concentration of the ZnO film, the conducting ZnO film can serve as broadband antireflection coatings for substrates and optics in the terahertz frequency range.
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73.61.Ga II-VI semiconductors
78.70.Gq Microwave and radio-frequency interactions
81.15.Cd Deposition by sputtering
68.55.ag Semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Hf II-VI semiconductors

Narrow-line coherently combined tapered laser diodes in a Talbot external cavity with a volume Bragg grating

David Paboeuf, Gaëlle Lucas-Leclin, Patrick Georges, Nicolas Michel, Michel Krakowski, Jun Lim, Slawomir Sujecki, and Eric Larkins

Appl. Phys. Lett. 93, 211102 (2008); http://dx.doi.org/10.1063/1.3036896 (3 pages) | Cited 12 times

Online Publication Date: 25 November 2008

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We present the phase locking of an array of index-guided tapered laser diodes. An external cavity based on the self-imaging Talbot effect has been built. A volume Bragg grating is used as the output coupler to stabilize and narrow the spectrum at 976 nm. A power of 1.7 W is achieved in the in-phase single main lobe mode with a high visibility. We have checked that each emitter is locked to the Bragg wavelength with a 100 pm spectrum linewidth. The experimental results compare well with numerical simulations performed with two-dimensional wide-angle finite difference beam propagation method.
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42.55.Px Semiconductor lasers; laser diodes
02.70.Bf Finite-difference methods
42.30.-d Imaging and optical processing
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Polarization-selective resonant photonic crystal photodetector

Jin-Kyu Yang, Min-Kyo Seo, In-Kag Hwang, Sung-Bock Kim, and Yong-Hee Lee

Appl. Phys. Lett. 93, 211103 (2008); http://dx.doi.org/10.1063/1.3036954 (3 pages) | Cited 10 times

Online Publication Date: 25 November 2008

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Resonance-assisted photonic crystal (PhC) slab photodetectors are demonstrated by utilizing six 7-nm-thick InGaAsP quantum wells. In order to encourage efficient photon coupling into the slab from the vertical direction, a coupled-dipole-cavity-array PhC structure is employed. Inheriting the characteristics of the dipole mode, this resonant detector is highly polarization selective and shows a 22-nm-wide spectral width. The maximum responsivity of 0.28 A/W, which is >20 times larger than that of the identical detector without the pattern, is observed near 1.56 μm.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
42.70.Qs Photonic bandgap materials
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

High order mode oscillation in a terahertz photonic-band-gap multibeam reflex klystron

Kyu-Ha Jang, Seok-Gy Jeon, Jung-Il Kim, Jong-Hyo Won, Jin-Kyu So, Seung-Ho Bak, Anurag Srivastava, Sun-Shin Jung, and Gun-Sik Park

Appl. Phys. Lett. 93, 211104 (2008); http://dx.doi.org/10.1063/1.3037026 (3 pages) | Cited 5 times

Online Publication Date: 25 November 2008

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TM330-like higher order mode was excited in a multibeam reflex klystron oscillator employing a hybrid photonic-band-gap (PBG) cavity using a three-dimensional particle-in-cell simulation. One side of a conventional metal cavity was replaced with a dielectric photonic crystal lattice to form a hybrid PBG resonator that uses lattice band-gap effects resulting in a more uniform field of a higher order mode as well as the exclusion of some conventional-cavity-type modes, thereby reducing mode competition. Simulated reflex klystron in the hybrid PBG cavity produced an output power much higher than could be delivered in a conventional metal cavity.
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84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)

Theory of exciton-polariton lasing at room temperature in ZnO microcavities

R. Johne, D. D. Solnyshkov, and G. Malpuech

Appl. Phys. Lett. 93, 211105 (2008); http://dx.doi.org/10.1063/1.3036895 (3 pages) | Cited 15 times

Online Publication Date: 26 November 2008

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We use the semiclassical Boltzmann equations to describe the exciton-polariton relaxation in a bulk ZnO microcavity at room temperature. We present kinetic phase diagrams which report the lasing threshold versus the main sample parameters, such as the polariton lifetime or the value of the Rabi splitting. We find that the polariton laser is operating close to the thermodynamic equilibrium in most cases which makes advantageous the use of microcavities showing very large Rabi splittings as it is the case in ZnO structures. We find that room temperature polariton lasing could be observed in the samples presently available.
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71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
71.35.-y Excitons and related phenomena
42.55.Px Semiconductor lasers; laser diodes
42.55.Sa Microcavity and microdisk lasers

Single mode emitting ridge waveguide quantum cascade lasers coupled to an active ring resonator filter

Julia Semmel, Wolfgang Kaiser, Holger Hofmann, Sven Höfling, and Alfred Forchel

Appl. Phys. Lett. 93, 211106 (2008); http://dx.doi.org/10.1063/1.3039057 (3 pages) | Cited 5 times

Online Publication Date: 26 November 2008

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Quantum cascade ridge waveguide lasers with coupled ring resonators have been fabricated. Coupling of an actively pumped microring resonator to a ridge waveguide device allows for filtering the numerous Fabry–Pérot modes emerging in the ridge waveguide. Due to the large free spectral range of the ring resonators mode selection is accomplished, resulting in stable single mode emission for an optimized design. Thus, side mode suppression ratios of up to 26 dB over a temperature range of 140 K are attained by on-chip coupling of a ridge waveguide device with a microsquare ring resonator. The tuning rate of the microring resonator laser is 0.40 nm/K. Output powers of several milliwatts are obtained.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.55.Sa Microcavity and microdisk lasers
42.60.Fc Modulation, tuning, and mode locking

High quantum efficiency back-illuminated GaN avalanche photodiodes

C. Bayram, J. L. Pau, R. McClintock, M. Razeghi, M. P. Ulmer, and D. Silversmith

Appl. Phys. Lett. 93, 211107 (2008); http://dx.doi.org/10.1063/1.3039061 (3 pages) | Cited 5 times

Online Publication Date: 26 November 2008

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Back-illuminated avalanche photodiodes (APDs) composed of heterojunctions of either p-GaN/i-GaN/n-AlGaN or p-GaN/i-GaN/n-GaN/n-AlGaN were fabricated on AlN templates. At low voltage, an external quantum efficiency of 57% at 352 nm with a bandpass response was achieved by using AlGaN in the n-layer. Dependency of gain and leakage current on mesa area for these heterojunction APDs were studied. Back-illumination via different wavelength sources was used to demonstrate the advantages of hole-initiated multiplication in GaN APDs.
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85.60.Dw Photodiodes; phototransistors; photoresistors
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Properties of excited xenon atoms in an alternating current plasma display panel

Han S. Uhm, Phil Y. Oh, and Eun H. Choi

Appl. Phys. Lett. 93, 211501 (2008); http://dx.doi.org/10.1063/1.3033225 (3 pages) | Cited 3 times

Online Publication Date: 24 November 2008

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The properties of excited xenon atoms in the discharge cells of a plasma display panel are investigated by measuring the excited atom density via laser absorption spectroscopy. The density of the excited xenon atoms in the metastable state increases from zero, reaches its peak, and decreases with time in the discharge cells, as expected from a theoretical model. The profile of an excited xenon atom is also studied in terms of the xenon mole fraction. The typical density of excited xenon atoms in a metastable state is on the order of 1013 atoms/cm3.
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85.60.Pg Display systems
52.75.-d Plasma devices
52.80.-s Electric discharges
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Narrow-band deep-ultraviolet light emitting device using Al1−xGdxN

Takashi Kita, Shinya Kitayama, Masashi Kawamura, Osamu Wada, Yoshitaka Chigi, Yoshihiro Kasai, Tetsuro Nishimoto, Hiroyuki Tanaka, and Mikihiro Kobayashi

Appl. Phys. Lett. 93, 211901 (2008); http://dx.doi.org/10.1063/1.3028341 (3 pages) | Cited 4 times

Online Publication Date: 24 November 2008

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We demonstrated mercury-free narrow-band deep-ultraviolet luminescence from field-emission devices with Al1−xGdxN thin films. The Al1−xGdxN thin films were grown on fused silica substrates by a radio frequency reactive magnetron sputtering method. The deposited film shows a strong c-axis preferential orientation. A resolution limited, narrow intra-4f luminescence line from Gd3+ ions has been observed at 315 nm. The luminescence spectrum depends on the growth temperature of the thin film, and the intensity varies as a function of the GdN mole fraction.
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85.60.Jb Light-emitting devices
81.15.Cd Deposition by sputtering
81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors

Synthesis and photoluminescence characteristics of color-tunable BaY2ZnO5:Eu3+ phosphors

Chih-Hao Liang, Yee-Cheng Chang, and Yee-Shin Chang

Appl. Phys. Lett. 93, 211902 (2008); http://dx.doi.org/10.1063/1.2998299 (3 pages) | Cited 30 times

Online Publication Date: 25 November 2008

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Color-tunable phosphors of BaY2−xEuxZnO5 (x = 0.001–0.9) were synthesized using a vibrating milled solid state reaction. The results indicate that the emission spectra of BaY2−xEuxZnO5 samples excited at 395 nm exhibit a series of shaped peaks assigned to the 5D0→7FJ (J = 0,1,2,3,4) transitions. Luminescence from the higher excited states, such as 5D1, 5D2, and 5D3, were also observed even though the Eu3+ concentration was up to x = 0.2. The chromaticity coordinate of BaY2−xEuxZnO5 phosphors varies with the Eu3+-doped concentrations from blue, white, to red, and which may be potentially applicable as a white light emitting phosphor for ultraviolet light emitting diodes.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.20.Wk Machining, milling
78.55.Hx Other solid inorganic materials

Optical response from lenslike semiconductor nipple arrays

H.-M. Wu, C.-M. Lai, and L.-H. Peng

Appl. Phys. Lett. 93, 211903 (2008); http://dx.doi.org/10.1063/1.3036629 (3 pages) | Cited 10 times

Online Publication Date: 25 November 2008

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The authors reported the use of recessive size reduction in self-assembled polystyrene sphere mask with anisotropic etching to form lenslike nipple arrays onto the surface of silicon and gallium nitride. These devices are shown to exhibit a filling factor near to an ideal close-packed condition and paraboloidlike etch profile with slope increased proportionally to the device aspect ratio. Specular reflectivity of less than 3% was observed over the visible spectral range for the 0.35-μm-period nipple-lens arrays. Using two-dimensional rigorous coupled-wave analysis, the latter phenomenon can be ascribed to a gradual index matching mechanism accessed by a high surface-coverage semiconductor nipple array structure.
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81.65.Cf Surface cleaning, etching, patterning
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Me Organic compounds and polymers
61.41.+e Polymers, elastomers, and plastics
85.40.Hp Lithography, masks and pattern transfer

Enhanced fluorescence from Eu3+ in low-loss silica glass-ceramic waveguides with high SnO2 content

S. N. B. Bhaktha, F. Beclin, M. Bouazaoui, B. Capoen, A. Chiasera, M. Ferrari, C. Kinowski, G. C. Righini, O. Robbe, and S. Turrell

Appl. Phys. Lett. 93, 211904 (2008); http://dx.doi.org/10.1063/1.3037224 (3 pages) | Cited 11 times

Online Publication Date: 25 November 2008

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We report on the sol-gel fabrication and characterization of (100−x)SiO2–xSnO2 (x = 8, 16, and 25 mol %) glass-ceramic waveguides doped with 1 mol % Eu3+. A suitable top-down thermal process led to the formation of SnO2 nanocrystals ∼ 4 nm embedding Eu3+ ions. The excitation spectra evidence the role of interband electronic transition of SnO2 nanocrystals on the luminescence of Eu3+. Monitoring the 5D0→7F2 Eu3+ emission, we observe about 15 times increase in the intensity of SnO2 absorption band, moving from x = 8 to 25 mol %. These waveguides also exhibit low losses, making them quite promising for development of high-gain integrated optical amplifiers.
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42.79.Gn Optical waveguides and couplers

A model for debris clouds produced by impact of hypervelocity projectiles on multiplate structures

Qingming Zhang, Renrong Long, Fenglei Huang, Li Chen, and Yuesheng Fu

Appl. Phys. Lett. 93, 211905 (2008); http://dx.doi.org/10.1063/1.3029747 (3 pages)

Online Publication Date: 25 November 2008

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Hypervelocity impact of spherical and cylindrical projectiles on multipate shields at velocities between 4 and 6 km/s was investigated experimentally. A model was developed to describe the motion of the debris clouds generated. Good agreement was obtained between the experimental and simulation results. The model is capable of predicting damage induced by the impact and can be applied to the optimization and design of multiplate shields.
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46.70.De Beams, plates, and shells
45.40.Gj Ballistics (projectiles; rockets)
46.55.+d Tribology and mechanical contacts
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High-quality quantum point contact in two-dimensional GaAs (311)A hole system

J. Shabani, J. R. Petta, and M. Shayegan

Appl. Phys. Lett. 93, 212101 (2008); http://dx.doi.org/10.1063/1.3036011 (3 pages) | Cited 3 times

Online Publication Date: 24 November 2008

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We studied ballistic transport across a quantum point contact (QPC) defined in a high-quality GaAs (311)A two-dimensional hole system using shallow etching and top gating. The QPC conductance exhibits up to 11 quantized plateaus. The ballistic one-dimensional subbands are tuned by changing the lateral confinement and the Fermi energy of the holes in the QPC. We demonstrate that the positions of the plateaus (in gate voltage), the source-drain data, and the negative magnetoresistance data can be understood in a simple model that takes into account the variation, with gate bias, of the hole density and the width of the QPC conducting channel.
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73.23.Ad Ballistic transport
73.50.Fq High-field and nonlinear effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.Ey III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.63.-b Electronic transport in nanoscale materials and structures

Charge detection in graphene quantum dots

J. Güttinger, C. Stampfer, S. Hellmüller, F. Molitor, T. Ihn, and K. Ensslin

Appl. Phys. Lett. 93, 212102 (2008); http://dx.doi.org/10.1063/1.3036419 (3 pages) | Cited 32 times

Online Publication Date: 24 November 2008

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We report measurements on a graphene quantum dot with an integrated graphene charge detector. The quantum dot device consists of a graphene island (diameter of ∼ 200 nm) connected to source and drain contacts via two narrow graphene constrictions. From Coulomb diamond measurements a charging energy of 4.3 meV is extracted. The charge detector is based on a 45 nm wide graphene nanoribbon placed approximately 60 nm from the island. We show that resonances in the nanoribbon can be used to detect individual charging events on the quantum dot. The charging induced potential change on the quantum dot causes a steplike change in the current in the charge detector. The relative change in the current ranges from 10% up to 60% for detecting individual charging events.
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71.10.Pm Fermions in reduced dimensions (anyons, composite fermions, Luttinger liquid, etc.)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
81.05.U- Carbon/carbon-based materials
81.07.Ta Quantum dots

Similarities in the kinetics of photocrystallization and photodarkening in a-Se

Robert E. Tallman, A. Reznik, B. A. Weinstein, S. D. Baranovskii, and J. A. Rowlands

Appl. Phys. Lett. 93, 212103 (2008); http://dx.doi.org/10.1063/1.3026173 (3 pages) | Cited 1 time

Online Publication Date: 24 November 2008

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The onset time of photocrystallization (PC) as a function of temperature in a-Se films designed for avalanche photodetectors is explored using Raman scattering experiments. The PC onset time τon is compared to the time-constant τIPD for irreversible photodarkening (IPD) studied in earlier work. Both τon and τIPD exhibit activated thermal behavior mediated by an energy barrier EB ∼ 0.7–0.95 eV. We suggest that the formation kinetics of PC and IPD in a-Se are governed by the same energy surface and configuration changes, occurring via photoinduced defects during the primary stage of crystallization.
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64.70.K- Solid-solid transitions
78.20.-e Optical properties of bulk materials and thin films
78.30.Am Elemental semiconductors and insulators
78.66.Db Elemental semiconductors and insulators
68.55.-a Thin film structure and morphology
61.43.Dq Amorphous semiconductors, metals, and alloys

Energy barriers at interfaces of (100)GaAs with atomic layer deposited Al2O3 and HfO2

V. V. Afanas’ev, M. Badylevich, A. Stesmans, G. Brammertz, A. Delabie, S. Sionke, A. O’Mahony, I. M. Povey, M. E. Pemble, E. O’Connor, P. K. Hurley, and S. B. Newcomb

Appl. Phys. Lett. 93, 212104 (2008); http://dx.doi.org/10.1063/1.3021374 (3 pages) | Cited 17 times

Online Publication Date: 24 November 2008

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Band alignment at the interfaces of (100)GaAs with Al2O3 and HfO2 grown using atomic layer deposition is determined using internal photoemission and photoconductivity measurements. Though the inferred conduction and valence band offsets for both insulators were found to be close to or larger than 2 eV, the interlayer grown by concomitant oxidation of GaAs reduces the barrier for electrons by approximately 1 eV. The latter may pose significant problems associated with electron injection from GaAs into the oxide.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
72.40.+w Photoconduction and photovoltaic effects
79.60.Jv Interfaces; heterostructures; nanostructures
77.55.-g Dielectric thin films
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Scaling behaviors of reset voltages and currents in unipolar resistance switching

S. B. Lee, S. C. Chae, S. H. Chang, J. S. Lee, S. Seo, B. Kahng, and T. W. Noh

Appl. Phys. Lett. 93, 212105 (2008); http://dx.doi.org/10.1063/1.3036532 (3 pages) | Cited 28 times

Online Publication Date: 25 November 2008

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The wide distributions of switching voltages in unipolar switching currently pose major obstacles for scientific advancement and practical applications. Using NiO capacitors, we investigated the distributions of the reset voltage and current. We found that they scaled with the resistance value Ro in the low resistance state and that the scaling exponents varied at Ro ≈ 30 Ω. We explain these intriguing scaling behaviors and their crossovers by analogy with percolation theory. We show that the connectivity of conducting filaments plays a crucial role in the reset process.
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84.32.Tt Capacitors
84.30.Sk Pulse and digital circuits
72.60.+g Mixed conductivity and conductivity transitions

Spin-glass-like behavior caused by Mn-rich Mn(Ga)As nanoclusters in GaAs

C. H. Chang and T. M. Hong

Appl. Phys. Lett. 93, 212106 (2008); http://dx.doi.org/10.1063/1.3039058 (3 pages) | Cited 1 time

Online Publication Date: 26 November 2008

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We simulate the indirect exchange interaction between Mn-rich Mn(Ga)As nanoclusters in GaAs by analytical means. In contrast to the conventional Ruderman–Kittel–Kasuya–Yosida (RKKY) formula, which considers the mediation by the carriers in the medium, we also include the contribution from those inside the clusters. Since the carrier concentration is higher in the clusters, this modification allows the RKKY oscillation to change its sign. Consequently, while the previous approach only favors ferromagnetism for this system, an antiferromagnetic coupling is in fact possible. Since the Mn-rich Mn(Ga)As nanoclusters are naturally formed and bound to have different sizes, their spin orientation is likely to be frustrated due to mixed preferences from different neighbors. We argue that this is likely the source of the spin-glass-like behavior that plagues this system. By tuning the size and narrowing its distribution, normal ferromagnetism can be restored with a Curie temperature higher than previously thought.
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68.35.Ct Interface structure and roughness
68.35.Fx Diffusion; interface formation
68.35.Rh Phase transitions and critical phenomena
46.65.+g Random phenomena and media

Surface potential of n- and p-type GaN measured by Kelvin force microscopy

S. Barbet, R. Aubry, M.-A. di Forte-Poisson, J.-C. Jacquet, D. Deresmes, T. Mélin, and D. Théron

Appl. Phys. Lett. 93, 212107 (2008); http://dx.doi.org/10.1063/1.3028639 (3 pages) | Cited 17 times

Online Publication Date: 26 November 2008

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n- and p-type GaN epitaxial layers grown by metal-organic chemical vapor deposition with different doping levels have been characterized by Kelvin probe force microscopy (KFM). To investigate the surface states of GaN beyond instrumental and environmental fluctuations, a KFM calibration procedure using a gold-plated Ohmic contact as a reference has been introduced, and the reproducibility of the KFM measurements has been evaluated. Results show that the Fermi level is pinned for n- and p-type GaN over the available doping ranges, and found 1.34±0.15 eV below the conduction band and 1.59±0.18 eV above the valence band, respectively.
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68.37.Ps Atomic force microscopy (AFM)
61.72.uj III-V and II-VI semiconductors
81.05.Ea III-V semiconductors
73.61.Ey III-V semiconductors
73.20.At Surface states, band structure, electron density of states
71.20.Nr Semiconductor compounds
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Ferromagnetic spin-correlations in strained LaCoO3 thin films

J. W. Freeland, J. X. Ma, and J. Shi

Appl. Phys. Lett. 93, 212501 (2008); http://dx.doi.org/10.1063/1.3027063 (3 pages) | Cited 6 times

Online Publication Date: 24 November 2008

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We present an element-resolved study of the valence and magnetic properties of LaCoO3 thin films grown via pulsed laser deposition. The Co L edge x-ray absorption shows that ferromagnetic (FM) order arises from a slight hole doping of the system presumably due to nonstoichiometry, which in the bulk system disrupts the low-spin state. However, even though the films are hole doped, the magnetic moments under tensile strain are much larger than the bulk system indicating that the strain can greatly increase the FM fraction observed in the spin-glass regime at low doping.
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75.70.Ak Magnetic properties of monolayers and thin films
78.70.Dm X-ray absorption spectra
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
75.30.Cr Saturation moments and magnetic susceptibilities
81.15.Fg Pulsed laser ablation deposition
75.50.Dd Nonmetallic ferromagnetic materials

Bias-dependent rectifying properties of n-n manganite heterojunctions La1−xCaxMnO3/SrTiO3:Nb (x = 0.65–1)

W. M. Lü, J. R. Sun, D. J. Wang, Y. W. Xie, S. Liang, Y. Z. Chen, and B. G. Shen

Appl. Phys. Lett. 93, 212502 (2008); http://dx.doi.org/10.1063/1.3021399 (3 pages) | Cited 3 times

Online Publication Date: 24 November 2008

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The transport property of n-n type manganite heterojunctions, composed of La1−xCaxMnO3 films (x = 0.6, 0.75, 0.85, and 1) and 0.05 wt % Nb-doped SrTiO3, has been experimentally studied. Different from p-n junctions, the rectifying behavior of which is either thermionic emission/diffusion-dominated or tunneling-dominated; the electronic process in the n-n junction undergoes a nonthermal to thermal transition as bias voltage increases, which is a feature emerging when Ca content exceeds x = 0.75 and developing with the increase in x. The two processes can be well described by the Shockley equation and the Newman equation, respectively. Possible mechanisms for this phenomenon are discussed.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
79.40.+z Thermionic emission
73.40.Ei Rectification
66.30.H- Self-diffusion and ionic conduction in nonmetals
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Pseudogap formation in the metallic state of La0.7Sr0.3MnO3 thin films

Udai Raj Singh, Anjan K. Gupta, Goutam Sheet, Venkat Chandrasekhar, H. W. Jang, and C. B. Eom

Appl. Phys. Lett. 93, 212503 (2008); http://dx.doi.org/10.1063/1.3028072 (3 pages) | Cited 6 times

Online Publication Date: 24 November 2008

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We report on scanning tunneling microscopy and spectroscopy (STM/S) studies of epitaxial La0.7Sr0.3MnO3 (LSMO) thin films on a lattice matched (001) La0.3Sr0.7Al0.35Ta0.35O9 substrate for both as-grown and annealed films. In contrast to the as-grown films, the films annealed at 800 °C in air show atomic terraces with spectra that develop a gaplike structure with cooling. We show that the gap structure can be attributed to the predicted pseudogap in the manganites. Unlike several previous reports, we did not find electronic inhomogeneities in LSMO by STM/S.
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71.20.Ps Other inorganic compounds
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Characterization of complementary electric field coupled resonant surfaces

Thomas H. Hand, Jonah Gollub, Soji Sajuyigbe, David R. Smith, and Steven A. Cummer

Appl. Phys. Lett. 93, 212504 (2008); http://dx.doi.org/10.1063/1.3037215 (3 pages) | Cited 9 times

Online Publication Date: 26 November 2008

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We present angle-resolved free-space transmission and reflection measurements of a surface composed of complementary electric inductive-capacitive (CELC) resonators. By measuring the reflection and transmission coefficients of a CELC surface with different polarizations and particle orientations, we show that the CELC only responds to in-plane magnetic fields. This confirms the Babinet particle duality between the CELC and its complement, the electric field coupled LC resonator. Characterization of the CELC structure serves to expand the current library of resonant elements metamaterial designers can draw upon to make unique materials and surfaces.
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84.40.Az Waveguides, transmission lines, striplines
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An extremely high dielectric constant in bismuth-based pyrochlore multilayer film capacitors combined with percolative structure

Nguyen Duy Cuong, Jun-Ku Ahn, Kyung-Woo Park, Nak-Jin Seong, and Soon-Gil Yoon

Appl. Phys. Lett. 93, 212901 (2008); http://dx.doi.org/10.1063/1.3013362 (3 pages) | Cited 4 times

Online Publication Date: 24 November 2008

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The percolative film capacitor structure of Pt/Bi2Mg2/3Nb4/3O7 [BMN(Ar) films deposited at pure argon atmosphere]/Pt was addressed for achievement of a high dielectric constant in the films deposited at room temperature by radio frequency magnetron sputtering. The deterioration of the leakage current characteristics in the percolative capacitor was mitigated using the multilayer films of BMN(O)/BMN(Ar)/BMN(O), where ultrathin BMN(O) films were deposited at a mixed atmosphere of argon and oxygen. An extremely high dielectric constant of 120 and a low leakage current density of 6×10−6 A/cm2 at 3 V were observed in percolative BMN multilayer films as-deposited at room temperature.
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77.22.Ch Permittivity (dielectric function)
81.15.Cd Deposition by sputtering
84.32.Tt Capacitors
68.65.Ac Multilayers
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