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22 Dec 2008

Volume 93, Issue 25, Articles (25xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 93, 251101 (2008); http://dx.doi.org/10.1063/1.3049138 (3 pages)

Masatoshi Fujimoto, Koji Matsukado, Hironori Takahashi, Yoichi Kawada, Shinji Ohsuka, and Shin-ichiro Aoshima
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Diagnosis of laser-induced relativistic plasma by positron imaging technique

Masatoshi Fujimoto, Koji Matsukado, Hironori Takahashi, Yoichi Kawada, Shinji Ohsuka, and Shin-ichiro Aoshima

Appl. Phys. Lett. 93, 251101 (2008); http://dx.doi.org/10.1063/1.3049138 (3 pages) | Cited 2 times

Online Publication Date: 22 December 2008

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Energetic deuterons emitted from laser-induced relativistic plasma are measured with a spatial resolution using a plate activated by them. Laser pulses of 33 TW in peak power and 34 fs in duration generate a plasma on a solid target, which is a microporous polytetrafluoroethylene film loaded with deuterated polystyrene, to accelerate deuterons. The deuterons are incident on a melamine plate, causing nuclear reactions of 12C(d,n)13N and 14N(d,n)15O. The spatial distributions of 13N and 15O created in the plate are visualized by a diagnosis using two-dimensional positron-emission tomography. The obtained images are further converted to temperature distribution of the emitted deuterons. The results show that the temperature of deuterons varies depending on the direction of deuteron emission. The present study provides knowledge of thermal equilibrium in laser-induced relativistic plasma in an ultrashort period of time.
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52.38.Kd Laser-plasma acceleration of electrons and ions
41.75.Jv Laser-driven acceleration

Epitaxial growth and Ohmic contacts in MgxZn1−xO/TiN/Si(111) heterostructures

Chunming Jin, Wei Wei, Honghui Zhou, Tsung-Han Yang, and Roger J. Narayan

Appl. Phys. Lett. 93, 251102 (2008); http://dx.doi.org/10.1063/1.3054347 (3 pages) | Cited 2 times

Online Publication Date: 22 December 2008

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In this work, the electronic properties of Mg0.1Zn0.9O/TiN/Si(111) heterostructures processed using pulsed laser deposition were examined. X-ray diffraction and transmission electron microscopy studies demonstrated epitaxial growth of the titanium nitride buffer layer and the Mg0.1Zn0.9O thin film. Transmission electron microscopy demonstrated a thin ( ∼ 5 nm) spinel layer along the magnesium zinc oxide/titanium nitride interface. Current-voltage measurements revealed Ohmic contact behavior through the magnesium zinc oxide/titanium nitride interface. These results suggest that the titanium nitride buffer layer in the MgxZn1−xO/TiN/Si(111) heterostructure provides a buffer layer for integrating magnesium zinc oxide thin films with silicon substrates, which both enable epitaxial growth and serve as an Ohmic electrode for the magnesium zinc oxide thin film.
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68.55.ag Semiconductors
73.40.Ty Semiconductor-insulator-semiconductor structures
81.15.Fg Pulsed laser ablation deposition

Near-field modal microscopy of subwavelength light confinement in multimode silicon slot waveguides

Kevin Foubert, Loïc Lalouat, Benoît Cluzel, Emmanuel Picard, David Peyrade, Eric Delamadeleine, Frédérique de Fornel, and Emmanuel Hadji

Appl. Phys. Lett. 93, 251103 (2008); http://dx.doi.org/10.1063/1.3040012 (3 pages) | Cited 8 times

Online Publication Date: 23 December 2008

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Silicon-on-insulator slot waveguides are studied by scanning near-field optical microscopy. Images of the standing wave pattern were established experimentally and compared with numerical simulations. Fourier analysis along the propagation direction reveals noticeable frequencies both on the experiment and the computation that could be related not only to the guided mode but also to beating phenomena between the coupled waveguides. Finally, light confinement above the slot is directly visualized with a subwavelength resolution and is compared with the expected field distribution.
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42.82.Et Waveguides, couplers, and arrays
42.30.Kq Fourier optics
07.79.Fc Near-field scanning optical microscopes

Enhanced stimulated Raman scattering in silicon nanocrystals embedded in silicon-rich nitride/silicon superlattice structures

L. Sirleto, M. A. Ferrara, I. Rendina, S. N. Basu, J. Warga, R. Li, and L. Dal Negro

Appl. Phys. Lett. 93, 251104 (2008); http://dx.doi.org/10.1063/1.3050109 (3 pages) | Cited 4 times

Online Publication Date: 23 December 2008

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In this paper, we report on the observation of stimulated Raman scattering in amorphous silicon nanocrystals embedded in Si-rich nitride/silicon superlattice structures (SRN/Si-SLs). In particular, we have experimentally demonstrated amplification of Stokes signal up to 0.9 dB/cm at 1540.6 nm using a 1427 nm continuous-wavelength pump laser, consistent with a preliminary valuation of approximately a fourfold enhancement of the gain coefficient in Raman amplifier based on SRN/Si-SLs with respect to silicon. Finally, a significant reduction in threshold power of about 40% is also reported. Our findings indicate that silicon nanocrystals embedded in Si nitride-based superlattice structures show great promise for Si-based Raman lasers.
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42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering
42.55.Ye Raman lasers
64.70.Nd Structural transitions in nanoscale materials
68.65.Cd Superlattices

Observation of spontaneous Raman scattering in silicon slow-light photonic crystal waveguides

J. F. McMillan, Mingbin Yu, Dim-Lee Kwong, and C. W. Wong

Appl. Phys. Lett. 93, 251105 (2008); http://dx.doi.org/10.1063/1.3050457 (3 pages) | Cited 16 times

Online Publication Date: 23 December 2008

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We report on the observation of spontaneous Raman scattering in silicon photonic crystal waveguides. Continuous-wave measurements of both forward scattered and backscattered Stokes emissions are reported in single line-defect waveguides in hexagonal lattice photonic crystal silicon membranes. By utilizing the Bragg gap edge dispersion of the TM-like mode for pump enhancement and the TE-like fundamental mode onset for Stokes enhancement, the spontaneous Raman scattering coefficient was observed to increase by up to six times in the region of slow group velocity. The results show explicit nonlinear enhancement in a silicon photonic crystal slow-light waveguide device.
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42.82.-m Integrated optics
42.82.Et Waveguides, couplers, and arrays
42.70.Qs Photonic bandgap materials
78.30.-j Infrared and Raman spectra

Ultrafast nonlinearities and gain dynamics in high-power semiconductor amplifiers

Ali R. Motamedi, Jason J. Plant, Joseph P. Donnelly, Paul W. Juodawlkis, and Erich P. Ippen

Appl. Phys. Lett. 93, 251106 (2008); http://dx.doi.org/10.1063/1.3056115 (3 pages) | Cited 1 time

Online Publication Date: 23 December 2008

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The limits imposed by two-photon absorption and free-carrier absorption on the gain and output powers of an InGaAsP/InP slab-coupled optical waveguide amplifier with a confinement factor of Γ = 0.5% were studied. The two-photon absorption coefficient and the induced free-carrier absorption cross section were measured to be 65 cm/GW and 7×10−17 cm2, respectively. The effects of two-photon absorption begin to limit the gain significantly for pulses shorter than 40 ps. The carrier recovery times were observed to vary between 390 and 160 ps for 1–4 A bias currents, and the short-pulse saturation fluence of the gain was determined to be 1.4 mJ/cm2.
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42.55.Px Semiconductor lasers; laser diodes
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.70.Hj Laser materials
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Field-resolved detection of phase-locked infrared transients from a compact Er:fiber system tunable between 55 and 107 THz

Alexander Sell, Rüdiger Scheu, Alfred Leitenstorfer, and Rupert Huber

Appl. Phys. Lett. 93, 251107 (2008); http://dx.doi.org/10.1063/1.3040057 (3 pages) | Cited 20 times

Online Publication Date: 24 December 2008

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We demonstrate phase-stable generation and ultrabroadband electro-optic detection of few-cycle multi-terahertz transients tunable from 55 to 107 THz based on a versatile telecom compatible three-branch Er:fiber laser system. Difference frequency mixing of two laser pulse trains at the full repetition rate of 49 MHz provides passively phase-locked multi-terahertz transients with peak fields of 69 kV/cm and average powers of up to 1.4 mW. 8 fs gating pulses from the third laser port allow for field-sensitive sampling throughout the midinfrared with a signal to noise ratio of up to 104 Hz1/2. A leadoff application in trace gas detection is discussed.
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42.60.Fc Modulation, tuning, and mode locking
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
42.55.Wd Fiber lasers
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Nanostructured multilayer graded-index antireflection coating for Si solar cells with broadband and omnidirectional characteristics

Sameer Chhajed, Martin F. Schubert, Jong Kyu Kim, and E. Fred Schubert

Appl. Phys. Lett. 93, 251108 (2008); http://dx.doi.org/10.1063/1.3050463 (3 pages) | Cited 60 times

Online Publication Date: 24 December 2008

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Design, fabrication, and characterization of a broadband, omnidirectional, graded-index antireflection (AR) coating made using nanostructured low-refractive-index (n = 1.05–1.40) silica deposited by oblique-angle deposition are reported. Averaged over wavelength range from 400 to 1100 nm and 0°–90° angle of incidence, polished Si reflects ∼ 37% of incident radiation. The reflection losses are reduced to only 5.9% by applying a three-layer graded-index AR coating to Si. Our experimental results are in excellent agreement with theoretical calculations. The AR coatings reported here can be optimized for photovoltaic cells made of any type of material.
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42.79.Wc Optical coatings
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Modal structure, directional and wavelength jumps of integrated semiconductor ring lasers: Experiment and theory

S. Fürst, A. Pérez-Serrano, A. Scirè, M. Sorel, and S. Balle

Appl. Phys. Lett. 93, 251109 (2008); http://dx.doi.org/10.1063/1.3052601 (3 pages) | Cited 12 times

Online Publication Date: 24 December 2008

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We have experimentally and theoretically analyzed the modal properties of semiconductor ring lasers and the wavelength jumps that occur in connection with directional switching above the threshold.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

onHigh-peak-power strain-compensated GaInAs/AlInAs quantum cascade lasers (λ ∼ 4.6 μm) based on a slightly diagonal active region design

Q. Yang, R. Lösch, W. Bronner, S. Hugger, F. Fuchs, R. Aidam, and J. Wagner

Appl. Phys. Lett. 93, 251110 (2008); http://dx.doi.org/10.1063/1.3054165 (3 pages) | Cited 10 times

Online Publication Date: 24 December 2008

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Employing a “slightly diagonal” active region design for the quantum cascade lasers compared to a reference sample based on the conventional vertical transition design [ R. Köhler et al., Appl. Phys. Lett. 76, 1092 (2000) ], we have improved the maximum operation temperature, room-temperature maximum peak power per facet, and room-temperature slope efficiency from 320 K, 200 mW, and 570 mW/A to higher than 360 K, 3.2 W, and 2200 mW/A, respectively, for the device size of 16 μm×3 mm with as-cleaved facets operated in pulsed mode.
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42.55.Px Semiconductor lasers; laser diodes
85.60.Bt Optoelectronic device characterization, design, and modeling
85.30.De Semiconductor-device characterization, design, and modeling

Transformation-optical design of sharp waveguide bends and corners

D. A. Roberts, M. Rahm, J. B. Pendry, and D. R. Smith

Appl. Phys. Lett. 93, 251111 (2008); http://dx.doi.org/10.1063/1.3055604 (3 pages) | Cited 32 times

Online Publication Date: 24 December 2008

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Transformation optics is a recently appreciated approach for designing complex electromagnetic media. Here, we describe the extension of transformation optical techniques to include waveguide boundary conditions. We illustrate the use of finite embedded coordinate transformations to design a medium that can be incorporated into a waveguide bend or corner, rendering the structure reflectionless. The expected behavior of the waveguide bends is confirmed with numerical simulations.
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42.79.Gn Optical waveguides and couplers
42.15.Eq Optical system design
42.70.-a Optical materials
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Tuning of plasmon propagation in two-dimensional electrons

Chao Li and X. G. Wu

Appl. Phys. Lett. 93, 251501 (2008); http://dx.doi.org/10.1063/1.3054645 (3 pages)

Online Publication Date: 22 December 2008

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It is shown theoretically that the propagation of plasmons can be tuned by an external electric field via spin-orbit interactions in a two-dimensional electron gas formed in a semiconductor heterostructure. This may provide a manageable way of transmitting quantum information in a quantum device. A possible plasmon field effect transistor is proposed.
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71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.30.Tv Field effect devices

Atmospheric glow discharges from the high-frequency to very high-frequency bands

J. L. Walsh, F. Iza, and M. G. Kong

Appl. Phys. Lett. 93, 251502 (2008); http://dx.doi.org/10.1063/1.3052857 (3 pages) | Cited 17 times

Online Publication Date: 23 December 2008

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This letter reports an experimental investigation of an atmospheric glow discharge in both the high-frequency (HF) band of 3–30 MHz and the very high frequency band of 30–300 MHz. At constant input power, increased frequency is found to change little the electron density and to reduce slightly the electron excitation temperature. Significantly, an eightfold frequency increase from 20 to 80 MHz leads to a 20-fold increase in the maximum plasma power without plasma constriction. The maximum power density of 355 W/cm3 achieved at 80 MHz is far greater than those reported in the HF band.
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52.80.Hc Glow; corona
52.80.Pi High-frequency and RF discharges
52.25.-b Plasma properties
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Hydrogen diffusion in MgH2 and NaMgH3 via concerted motions of charged defects

Shiqiang Hao and David S. Sholl

Appl. Phys. Lett. 93, 251901 (2008); http://dx.doi.org/10.1063/1.3046737 (3 pages) | Cited 17 times

Online Publication Date: 22 December 2008

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The transport properties of hydrogen in metal hydrides are crucial to the kinetics of H2 storage in these materials. We use first principles calculations to identify the defects that are relevant for H transport in MgH2 and NaMgH3. In both materials, the physically relevant defects are charged and H diffusion is dominated by mobility of negatively charged interstitial H. Moreover, the diffusion of these species occurs via concerted “interstitialcy” mechanisms with low energy barriers. Our results indicate that any examination of H diffusion in light metal hydrides must consider the concerted diffusion of charged defects.
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66.30.Lw Diffusion of other defects
84.60.-h Direct energy conversion and storage
61.72.jj Interstitials
61.72.jd Vacancies

Method to analyze programmable deformation of dielectric elastomer layers

Xuanhe Zhao and Zhigang Suo

Appl. Phys. Lett. 93, 251902 (2008); http://dx.doi.org/10.1063/1.3054159 (3 pages) | Cited 17 times

Online Publication Date: 22 December 2008

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A layer of a dielectric elastomer expands its area when a voltage is applied across its thickness. The layer can be programed to deform in three dimensions by using patterned prestretches, electrodes, and stiffeners. To aid the design of such programmable deformation, this paper describes a computational method, exploiting the fact that the prescribed voltage sets the nominal electric field. The method is demonstrated with examples including formation of wrinkles, movements of a handlike actuator, and nonlinear oscillation of a balloon.
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77.65.-j Piezoelectricity and electromechanical effects
77.84.Jd Polymers; organic compounds
82.45.Fk Electrodes
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Metamaterial polarizers by electric-field-coupled resonators

Jessie Y. Chin, Mingzhi Lu, and Tie Jun Cui

Appl. Phys. Lett. 93, 251903 (2008); http://dx.doi.org/10.1063/1.3054161 (3 pages) | Cited 22 times

Online Publication Date: 22 December 2008

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The idea of transmission polarizers realized by anisotropic metamaterials is demonstrated by experiments. One of the polarizers converts linear-polarized waves to circular-polarized waves, while the other polarizer converts linear-polarized waves from one polarization to its cross polarization. The excellent agreement between experimental results and theoretical predictions validates the functions and efficiency of the proposed polarizers.
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42.70.-a Optical materials
42.79.Ci Filters, zone plates, and polarizers

Effect of misfit strain on the multiferroism and nonlinear optical response in epitaxial PbVO3 thin films

Sheng Ju and Tian-Yi Cai

Appl. Phys. Lett. 93, 251904 (2008); http://dx.doi.org/10.1063/1.3050526 (3 pages) | Cited 3 times

Online Publication Date: 23 December 2008

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Based on density functional theory (the generalized gradient approximation plus on-site Coulomb repulsion method), we investigate the misfit strain dependence of multiferroism and second-harmonic generation (SHG) in epitaxial PbVO3 thin films. G-type antiferromagnetic ordering, large polar distortion, and significant SHG susceptibilities are revealed in PbVO3 over a wide range of substrates. In particular, the low frequency SHG susceptibility reaches as high as 300×10−9 esu in all the cases we considered, providing solid evidence of its potential application in nonlinear optoelectronic device.
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75.50.Ee Antiferromagnetics
75.70.Ak Magnetic properties of monolayers and thin films
75.80.+q Magnetomechanical effects, magnetostriction
78.66.Nk Insulators
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
68.60.Bs Mechanical and acoustical properties

Growth of biepitaxial zinc oxide thin films on silicon (100) using yttria-stabilized zirconia buffer layer

Ravi Aggarwal, Chunming Jin, Punam Pant, J. Narayan, and Roger J. Narayan

Appl. Phys. Lett. 93, 251905 (2008); http://dx.doi.org/10.1063/1.3050529 (3 pages) | Cited 4 times

Online Publication Date: 23 December 2008

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In this work, an approach for integrating zinc oxide thin films with Si(100) substrates using an epitaxial tetragonal yttria-stabilized zirconia buffer layer is reported. Selected area electron diffraction measurements revealed the following epitaxial relationship: [110]YSZ∥[100]Si and (001)YSZ∥(001)Si. X-ray diffraction studies demonstrated that subsequent growth of the zinc oxide thin film on the yttria-stabilized zirconia buffer layer occurred with the following epitaxial relationship: (0002)ZnO∥(001)YSZ. The full width at half maximum value for the (0002) peak of zinc oxide was small ( ∼ 0.16°), which indicated good crystalline quality. Transmission electron microscopy revealed that the zinc oxide thin film grew epitaxially on an yttria-stabilized zirconia buffer layer in two different orientations, where one orientation was rotated by 30° from the other. The orientation relationship in this case was [10math0]ZnO∥[100]YSZ or [2mathmath0]ZnO∥[100]YSZ and (0002)ZnO∥(001)YSZ. The biepitaxial growth of the zinc oxide thin film has been explained in the framework of domain matching epitaxy. Optical emission measurements showed a strong excitonic emission peak from the zinc oxide thin film at ∼ 377 nm. Minimal green band emission in the photoluminescence spectrum indicated that the concentration of point defects was low. Integration of epitaxial zinc oxide thin films with Si(100) substrates is an important step toward developing practical applications of zinc oxide in a variety of optoelectronic devices.
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81.15.Fg Pulsed laser ablation deposition
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors
68.37.Og High-resolution transmission electron microscopy (HRTEM)

Epitaxial growth of GaN films grown on single crystal Fe substrates

K. Okamoto, S. Inoue, N. Matsuki, T.-W. Kim, J. Ohta, M. Oshima, H. Fujioka, and A. Ishii

Appl. Phys. Lett. 93, 251906 (2008); http://dx.doi.org/10.1063/1.3056117 (3 pages) | Cited 3 times

Online Publication Date: 23 December 2008

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GaN films have been grown on single crystalline Fe(110), Fe(100), and Fe(111) substrates with low-temperature AlN buffer layers by the use of pulsed laser deposition. AlN films with 30° rotated domains and polycrystalline AlN films grow on Fe(100) and Fe(111), respectively. On the other hand, AlN(0001) films grow epitaxially on Fe(110) substrates. X-ray reflectivity measurements have revealed that the heterointerface of AlN/Fe(110) is quite abrupt and that its abruptness remains unchanged, even after annealing at 700 °C. GaN epitaxial films have been grown on AlN/Fe(110) structures with an in-plane relationship of GaN[11−20]∥AlN[11−20]∥Fe[001]. The first-principles calculations have revealed that this in-plane epitaxial relationship is determined by the adsorption process of nitrogen atoms on the Fe surfaces at the initial stage of the growth.
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68.55.ag Semiconductors
68.43.De Statistical mechanics of adsorbates
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
68.43.Mn Adsorption kinetics
81.15.Fg Pulsed laser ablation deposition
61.72.Cc Kinetics of defect formation and annealing

Viscoelastic mechanical behavior of soft microcantilever-based force sensors

I-Kuan Lin, Yen-Ming Liao, Yan Liu, Kuang-Shun Ou, Kuo-Shen Chen, and Xin Zhang

Appl. Phys. Lett. 93, 251907 (2008); http://dx.doi.org/10.1063/1.3056114 (3 pages) | Cited 10 times

Online Publication Date: 24 December 2008

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Polydimethylsiloxane (PDMS) microcantilevers have been used as force sensors for studying cellular mechanics by converting their displacements to cellular mechanical forces. However, PDMS is an inherently viscoelastic material and its elastic modulus changes with loading rates and elapsed time. Therefore, the traditional approach to calculating cellular mechanical forces based on elastic mechanics can result in errors. This letter reports a more in-depth method for viscoelastic characterization, modeling, and analysis associated with the bending behavior of the PDMS microcantilevers. A viscoelastic force conversion model was developed and validated by proof-of-principle bending tests.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Pz Instruments for strain, force, and torque
07.10.Cm Micromechanical devices and systems
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Observation of electric field-assisted phase transition in thin film vanadium oxide in a metal-oxide-semiconductor device geometry

Changhyun Ko and Shriram Ramanathan

Appl. Phys. Lett. 93, 252101 (2008); http://dx.doi.org/10.1063/1.3050464 (3 pages) | Cited 33 times

Online Publication Date: 22 December 2008

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We report the observation of electric field-assisted phase transition across a vanadium oxide thin film. The threshold field for initiation of transition was ∼ 107 V/m at room temperature and decreased with increasing temperature with activation energy of ∼ 0.2 eV. Electron transport mechanisms were investigated using both current-in-plane and out-of-plane devices and the results correlated very well. In the insulator phase, Poole–Frenkel emission was determined to be a dominant mechanism at high fields, while in the low field regime, Ohmic behavior with activation energy of ∼ 0.24 eV was observed. In the metallic state, activation energy for Ohmic conduction was ∼ 0.08 eV.
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71.30.+h Metal-insulator transitions and other electronic transitions
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.50.Fq High-field and nonlinear effects

Strong resistance nonlinearity and third harmonic generation in the unipolar resistance switching of NiO thin films

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

Appl. Phys. Lett. 93, 252102 (2008); http://dx.doi.org/10.1063/1.3050519 (3 pages) | Cited 8 times

Online Publication Date: 22 December 2008

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We investigated third harmonic generation in NiO thin films that exhibit unipolar resistance switching. We found that low resistance states (LRSs) were strongly nonlinear with variations in the resistance R as large as 60%, which was most likely caused by the Joule heating of conducting filaments inside the films. By carefully controlling the applied dc bias, we obtained several LRSs, whose values of the third harmonic coefficient B3f were proportional to R2+w (w = 2.07±0.26). This suggested that the resistance changes in the NiO films were accompanied by connectivity changes of the conducting filaments, as observed in classical percolating systems.
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73.61.At Metal and metallic alloys

Low-temperature-fabricated InGaZnO4 thin film transistors on polyimide clean-room tape

Wantae Lim, E. A. Douglas, S.-H. Kim, D. P. Norton, S. J. Pearton, F. Ren, H. Shen, and W. H. Chang

Appl. Phys. Lett. 93, 252103 (2008); http://dx.doi.org/10.1063/1.3054167 (3 pages) | Cited 12 times

Online Publication Date: 22 December 2008

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Amorphous (α-)InGaZnO4 thin film transistors (TFTs) were fabricated on polyimide clean-room tape at low temperature (<100 °C). The α-InGaZnO4 films with an n-type carrier concentration of ∼ 1016 cm−3 were deposited by rf-magnetron sputtering in a mixed ambient of Ar/O2. The bottom-gate-type TFTs showed good saturation mobility ( ∼ 5.3 cm2 V−1 s−1), drain current on-to-off ratio of approximately 105, threshold voltage of 1.1 V, and subthreshold gate-voltage swing of 0.55 V decade−1. These results were comparable to those of the same oxide TFTs that we have fabricated on either glass or polyethylene terephthalate substrates. The results demonstrate that even polyimide clean-room tape can be an appropriate substrate for inexpensive-flexible-adhesive-transparent electronic devices.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
72.20.Fr Low-field transport and mobility; piezoresistance

Bipolar charge transport in poly(3-hexyl thiophene)/methanofullerene blends: A ratio dependent study

A. Baumann, J. Lorrmann, C. Deibel, and V. Dyakonov

Appl. Phys. Lett. 93, 252104 (2008); http://dx.doi.org/10.1063/1.3055608 (3 pages) | Cited 28 times

Online Publication Date: 22 December 2008

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We investigated the charge carrier mobility in pristine poly(3-hexyl thiophene-2,5-diyl) (P3HT):[6,6]-phenyl-C61 butyric acid methyl ester (PCBM) blend devices by applying the time resolved photoconductivity experiment in dependence on the donor:acceptor ratio. We observe a bipolar transport in all studied samples ranging from pure polymer to polymer:fullerene with 90% PCBM content. For the ratios P3HT:PCBM 1:4 and 1:1 we observe two transit times in the electron current transients as well as hole double transients for P3HT:PCBM 1:2. We find high hole and electron mobilities in the order of 10−3–10−2 cm2/V s for a concentration of 90% PCBM in the blend.
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72.20.Ee Mobility edges; hopping transport
84.60.Jt Photoelectric conversion
78.47.-p Spectroscopy of solid state dynamics
72.80.Le Polymers; organic compounds (including organic semiconductors)
71.55.Ht Other nonmetals
72.40.+w Photoconduction and photovoltaic effects

Effects of high-temperature annealing on the optical phonons and nitrogen local vibrational modes in GaAs1−xNx epilayers

J. A. H. Coaquira, J. F. Teixeira, S. W. da Silva, P. C. Morais, A. Fotkatzikis, and A. Freundlich

Appl. Phys. Lett. 93, 252105 (2008); http://dx.doi.org/10.1063/1.3056113 (3 pages)

Online Publication Date: 22 December 2008

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Effects of high-temperature annealing on the vibrational properties of strained GaAs1−xNx/GaAs epilayers with x ⩽ 0.037 have been studied by room-temperature backscattering Raman measurements. The reduction in the linear redshift of the LO1 line after the annealing, commonly related to strain relaxation, must be associated with the change in the plasma screening effect in our samples. For x<0.02, the linear tendency of the LO2 line frequency for as-grown samples remains unchanged after the annealing. However, that line frequency deviates from a polynomial behavior to a linear trend after the annealing for x>0.02. This change in behavior has been assigned to the reduction in N–N pairs and concomitantly to the increase in substitutional N promoted by the annealing.
Show PACS
61.72.Cc Kinetics of defect formation and annealing
63.20.-e Phonons in crystal lattices
78.66.Fd III-V semiconductors
68.55.ag Semiconductors
78.30.Fs III-V and II-VI semiconductors
63.20.Pw Localized modes
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
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