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23 Nov 2009

Volume 95, Issue 21, Articles (21xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 95, 213501 (2009); http://dx.doi.org/10.1063/1.3265958 (3 pages)

S. Cibella, M. Ortolani, R. Leoni, G. Torrioli, L. Mahler, Ji-Hua Xu, A. Tredicucci, H. E. Beere, and D. A. Ritchie
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Ferromagnetic to weak-magnetic transition accompanied by bcc to fcc transformation in Fe–Mn–Al alloy

K. Ando, T. Omori, I. Ohnuma, R. Kainuma, and K. Ishida

Appl. Phys. Lett. 95, 212504 (2009); http://dx.doi.org/10.1063/1.3266848 (3 pages) | Cited 6 times

Online Publication Date: 25 November 2009

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Magnetic properties and phase change in Fe-36 at. %Mn-15 at. %Al ternary alloy were investigated. Direct evidence of a ferromagnetic to weak-magnetic transition accompanied by martensitic transformation from the bcc-α (A2) phase to the fcc-γ′ (2M) phase was obtained, where the magnetic state of the parent and the martensite phases are ferromagnetic and weak-magnetic, respectively. The origin of this unique phase change is caused by the peculiar γ-loop of α/γ equilibrium formed in Fe–Mn–X (X: ferrite stabilizing element) system due to the magnetic effect.
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75.50.Bb Fe and its alloys
81.30.Kf Martensitic transformations
64.70.kd Metals and alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Weak-link behavior of grain boundaries in superconducting Ba(Fe1−xCox)2As2 bicrystals

S. Lee, J. Jiang, J. D. Weiss, C. M. Folkman, C. W. Bark, C. Tarantini, A. Xu, D. Abraimov, A. Polyanskii, C. T. Nelson, Y. Zhang, S. H. Baek, H. W. Jang, A. Yamamoto, F. Kametani, et al.

Appl. Phys. Lett. 95, 212505 (2009); http://dx.doi.org/10.1063/1.3262953 (3 pages) | Cited 57 times

Online Publication Date: 25 November 2009

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We show that despite the low anisotropy, strong vortex pinning, and high irreversibility field Hirr close to the upper critical field Hc2 of Ba(Fe1−xCox)2As2, the critical current density Jgb across [001] tilt grain boundaries (GBs) of thin film Ba(Fe1−xCox)2As2 bicrystals is strongly depressed, similar to high-Tc cuprates. Our results suggest that weak-linked GBs are characteristic of both cuprates and pnictides because of competing orders, low carrier density, and unconventional pairing symmetry.
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74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.25.Wx Vortex pinning (includes mechanisms and flux creep)
74.25.Sv Critical currents
61.72.Mm Grain and twin boundaries
74.70.Xa Pnictides and chalcogenides
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Epitaxial growth of (001)-oriented Ba0.5Sr0.5TiO3 thin films on a-plane sapphire with an MgO/ZnO bridge layer

Bo Xiao, Hongrui Liu, Vitaliy Avrutin, Jacob H. Leach, Emmanuel Rowe, Huiyong Liu, Ümit Özgür, Hadis Morkoç, W. Chang, L. M. B. Alldredge, S. W. Kirchoefer, and J. M. Pond

Appl. Phys. Lett. 95, 212901 (2009); http://dx.doi.org/10.1063/1.3266862 (3 pages) | Cited 10 times

Online Publication Date: 23 November 2009

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High quality (001)-oriented Ba0.5Sr0.5TiO3 (BST) thin films have been grown on a-plane sapphire (11math0) by rf magnetron sputtering using a double bridge layer consisting of (0001)-oriented ZnO (50 nm) and (001)-oriented MgO (10 nm) prepared by plasma-assisted molecular beam epitaxy. X-ray diffraction revealed the formation of three sets of in-plane BST domains, offset from one another by 30°, which is consistent with the in-plane symmetry of the MgO layer observed by in situ reflective high electron energy diffraction. The in-plane epitaxial relationship of BST, MgO, and ZnO has been determined to be BST [110]//MgO [110]//ZnO [11math0] and BST [110]/MgO [110]//ZnO [1math00]. Capacitance-voltage measurements performed on BST coplanar interdigitated capacitor structures revealed a high dielectric tunability of up to 84% at 1 MHz.
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68.55.-a Thin film structure and morphology
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
68.55.A- Nucleation and growth
81.15.Cd Deposition by sputtering

Characterization of the “clean-up” of the oxidized Ge(100) surface by atomic layer deposition

M. Milojevic, R. Contreras-Guerrero, M. Lopez-Lopez, J. Kim, and R. M. Wallace

Appl. Phys. Lett. 95, 212902 (2009); http://dx.doi.org/10.1063/1.3268449 (3 pages) | Cited 10 times

Online Publication Date: 24 November 2009

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While the “clean-up” effect on III-V substrates has recently been well documented interfacial reactions during atomic layer deposition (ALD) on Ge substrates are not fully explored. The “clean-up” of Ge oxides is studied by interrupting the ALD process following individual precursor pulses for in situ monochromatic x-ray photoelectron spectroscopy analysis. Germanium oxides are found to be reduced by TMA and water, while an interfacial GeON layer is only affected by the initial TMA pulse. Oxide free germanium surfaces behave analogously to a surface with initial native oxides since they are oxidized measurably prior to the first TMA pulse due to residual oxidants in a commercial ALD chamber.
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79.60.Bm Clean metal, semiconductor, and insulator surfaces
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Interaction of La2O3 capping layers with HfO2 gate dielectrics

M. Copel, S. Guha, N. Bojarczuk, E. Cartier, V. Narayanan, and V. Paruchuri

Appl. Phys. Lett. 95, 212903 (2009); http://dx.doi.org/10.1063/1.3268456 (3 pages) | Cited 14 times

Online Publication Date: 24 November 2009

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We report the effect of La2O3 capping layers on HfO2/SiO2/Si dielectrics, proposed for use in threshold voltage tuning of field effect transistors. Depth profiling with medium energy ion scattering shows that an initial surface layer of La2O3 diffuses through the HfO2 at elevated temperatures, ultimately converting some of the thin interfacial SiO2 into a silicate. Core-level photoemission measurements indicate that the additional band-bending induced by the La2O3 only appears after diffusion, and the added charge resides between the HfO2 and the substrate.
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77.55.-g Dielectric thin films
66.30.Ny Chemical interdiffusion; diffusion barriers
85.30.Tv Field effect devices
79.60.Jv Interfaces; heterostructures; nanostructures
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Vertically aligned ZnO nanostructures grown on graphene layers

Yong-Jin Kim, Jae-Hyun Lee, and Gyu-Chul Yi

Appl. Phys. Lett. 95, 213101 (2009); http://dx.doi.org/10.1063/1.3266836 (3 pages) | Cited 36 times

Online Publication Date: 24 November 2009

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We report the vertical growth of ZnO nanostructures on graphene layers and their photoluminescence (PL) characteristics. ZnO nanostructures were grown vertically on the graphene layers using catalyst-free metal-organic vapor-phase epitaxy. The surface morphology of the ZnO nanostructures on the graphene layers depended strongly on the growth temperature. Further, interesting growth behavior leading to the formation of aligned ZnO nanoneedles in a row and vertically aligned nanowalls was also observed and explained in terms of enhanced nucleation on graphene step edges and kinks. Additionally, the optical characteristics and carbon incorporation into ZnO were investigated using variable-temperature PL spectroscopy.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
61.46.-w Structure of nanoscale materials
68.35.bg Semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.55.Et II-VI semiconductors
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures

Emission properties of Ag/dielectric/Ag plasmonic thermal emitter with different lattice type, hole shape, and dielectric material

Yi-Tsung Chang, Yi-Tin Wu, Jheng-Han Lee, Hung-Hsin Chen, Chun-Yuan Hsueh, Hao-Fu Huang, Yu-Wei Jiang, Pei-En Chang, and Si-Chen Lee

Appl. Phys. Lett. 95, 213102 (2009); http://dx.doi.org/10.1063/1.3266868 (3 pages) | Cited 7 times

Online Publication Date: 24 November 2009

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The emission spectra of the trilayer Ag/dielectric/Ag plasmonic thermal emitter (PTE) with different lattice type, hole shape, and dielectric material were investigated. It is found that the position and number of thermal emission peak of the PTE are determined by the lattice type not by the hole shape and dielectric materials. The PTE with hexagonal lattice generates only one strong (1,0) Ag/dielectric emission peak, whereas a similar PTE with square lattice generates two strong (1,0) and (1,1) Ag/dielectric emission peaks, their relative intensities follow the blackbody radiation law. This phenomenon suggests the coupling of Ag/dielectric and Ag/air modes.
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79.60.Jv Interfaces; heterostructures; nanostructures
63.22.Np Layered systems
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

A computational study of tunneling-percolation electrical transport in graphene-based nanocomposites

Jeremy Hicks, Ashkan Behnam, and Ant Ural

Appl. Phys. Lett. 95, 213103 (2009); http://dx.doi.org/10.1063/1.3267079 (3 pages) | Cited 9 times

Online Publication Date: 24 November 2009

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Using a tunneling-percolation model and Monte Carlo simulations, we study the resistivity of graphene-based nanocomposites as a function of both graphene sheet and device parameters. We observe an inverse power law dependence of resistivity on device dimensions and volume fraction near the percolation threshold, and find that high aspect ratio graphene sheets result in a much lower resistivity, particularly at low sheet densities. Furthermore, we find that graphene sheet area affects nanocomposite resistivity more strongly than sheet density does. These results impart important fundamental insights for future experimental investigations and applications of graphene-based conductive nanocomposites.
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73.61.Wp Fullerenes and related materials
73.40.Gk Tunneling
61.46.-w Structure of nanoscale materials
61.48.Gh Structure of graphene

Tailoring light emission properties of organic emitter by coupling to resonance-tuned silver nanoantenna arrays

Teng Qiu, Fan Kong, Xiaoqiang Yu, Wenjun Zhang, Xianzhong Lang, and Paul K. Chu

Appl. Phys. Lett. 95, 213104 (2009); http://dx.doi.org/10.1063/1.3269190 (3 pages) | Cited 11 times

Online Publication Date: 25 November 2009

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A convenient nanotechnique is reported to tailor the light emission properties of organic emitter poly[2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV) by coupling to resonance-tuned silver nanoantenna arrays. It is revealed experimentally and theoretically that the enhanced photoluminescence from the MEH-PPV/silver nanoantenna complex may originate from the energy transfer effect in the surface plasmon resonance coupling between the MEH-PPV and silver nanocaps and from local electromagnetic field enhancement of nanogaps between the silver nanocaps in the background of the light-emitting MEH-PPV. The results are corroborated by the finite difference time domain simulation results.
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78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.55.-m Photoluminescence, properties and materials
73.22.Lp Collective excitations
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
81.16.-c Methods of micro- and nanofabrication and processing

Grain size dependence of electrical and optical properties in Nb-doped anatase TiO2

J. Y. Yang, W. S. Li, H. Li, Y. Sun, R. F. Dou, C. M. Xiong, L. He, and J. C. Nie

Appl. Phys. Lett. 95, 213105 (2009); http://dx.doi.org/10.1063/1.3266867 (3 pages) | Cited 8 times

Online Publication Date: 25 November 2009

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Anatase thin films of pure TiO2 and 6% niobium doped TiO2 (Nb:TiO2) were fabricated on LaAlO3(100) by pulsed laser deposition. The electrical properties of Nb:TiO2 films are grain-size dependent, i.e., the larger grain size, the higher conductivity, and mobility. For all TiO2 and for Nb:TiO2 with small mean grain size (d<15 nm), the band gap energy is found to increase systematically with the decrease in d, which is consistent with the quantum confinement model. For the films with large mean grain size (d>15 nm), particularly, a blueshift in Nb:TiO2 is governed by the Burstein–Moss effect.
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78.66.-w Optical properties of specific thin films
73.61.-r Electrical properties of specific thin films
81.15.Fg Pulsed laser ablation deposition

Robust localized modes in bilayer graphene induced by an antisymmetric kink potential

J. C. Martinez, M. B. A. Jalil, and S. G. Tan

Appl. Phys. Lett. 95, 213106 (2009); http://dx.doi.org/10.1063/1.3263150 (3 pages) | Cited 3 times

Online Publication Date: 25 November 2009

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When bilayer graphene is gated with a kink potential, pair particle localization occurs at the kink where a particle (electron) and its chiral partner (hole) are held in balance by electrostatic coupling. Zero-energy states (zero modes) are always present in pairs and occur at the same point in the dispersion graph, regardless of kink strength. The robust and binary nature of the kink-induced modes, which are topologically protected against disorder, and the ease with which a kink is created suggest applications in switching devices or information storage.
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63.22.Rc Phonons in graphene
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Patterned electrode vertical field effect transistor fabricated using block copolymer nanotemplates

Ariel J. Ben-Sasson, Eran Avnon, Elina Ploshnik, Oded Globerman, Roy Shenhar, Gitti L. Frey, and Nir Tessler

Appl. Phys. Lett. 95, 213301 (2009); http://dx.doi.org/10.1063/1.3266855 (3 pages) | Cited 10 times

Online Publication Date: 23 November 2009

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We report the design and implementation of a vertical organic field effect transistor which is compatible with standard device fabrication technology and is well described by a self consistent device model. The active semiconductor is a film of C60 molecules, and the device operation is based on the architecture of the nanopatterned source electrode. The relatively high resolution fabrication process and maintaining the low-cost and simplicity associated with organic electronics, necessitates unconventional fabrication techniques such as soft lithography. Block copolymer self-assembled nanotemplates enable the production of conductive, gridlike metal electrode. The devices reported here exhibit On/Off ratio of 104.
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85.30.Tv Field effect devices
81.16.Nd Micro- and nanolithography
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C60 cluster formation at interfaces with pentacene thin-film phases

B. R. Conrad, J. Tosado, G. Dutton, D. B. Dougherty, W. Jin, T. Bonnen, A. Schuldenfrei, W. G. Cullen, E. D. Williams, J. E. Reutt-Robey, and S. W. Robey

Appl. Phys. Lett. 95, 213302 (2009); http://dx.doi.org/10.1063/1.3266857 (3 pages) | Cited 5 times

Online Publication Date: 24 November 2009

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The C60-thin film pentacene interface was investigated using scanning tunneling microscopy, atomic force microscopy, and ultraviolet photoemission spectroscopy. C60 deposition on a multilayer pentacene film (standing) yields an interface dominated by C60 clusters, regardless of the underlying substrate. Three-dimensional cluster growth dominates due to weak interactions with the underlying Pn. C60 cluster size and density on sequential Pn layers suggest an Ehrlich–Schwoebel-type barrier at Pn layer boundaries. Cluster formation reduces the C60 lowest unoccupied molecular orbital–Pn highest occupied molecular orbital (HOMO) separation, while increasing the respective HOMO-HOMO offset. Heterostructure fabrication protocols can alter interface morphology and induce band shifts on the order of 0.3 eV.
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36.40.-c Atomic and molecular clusters
71.20.Rv Polymers and organic compounds
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
81.05.Fb Organic semiconductors
07.79.Cz Scanning tunneling microscopes
07.79.Lh Atomic force microscopes
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Solution-processed conjugated polymer organic p-i-n light-emitting diodes with high built-in potential by solution- and solid-state doping

Sankaran Sivaramakrishnan, Mi Zhou, Aravind C. Kumar, Zhi-Li Chen, Rui-Qi Png, Lay-Lay Chua, and Peter K. H. Ho

Appl. Phys. Lett. 95, 213303 (2009); http://dx.doi.org/10.1063/1.3257979 (3 pages) | Cited 7 times

Online Publication Date: 24 November 2009

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Polymer p-i-n homojunction light-emitting diodes (LEDs) comprising p-doped poly(dioctylfluorene-alt-benzothiadiazole) (F8BT) hole-injection, intrinsic F8BT emitter, and n-doped F8BT electron-injection layers have been demonstrated. A thin F8BT film was photocrosslinked and bulk p-doped by nitronium oxidation, then overcoated with an F8BT layer which was then surface n-doped by contact printing with naphthalenide on an elastomeric stamp. These LEDs exhibit high built-in potential (Vbi = 2.2 V), efficient bipolar injection, and greatly improved external electroluminescence efficiency compared to control devices without the p-i-n structure. A modulated photocurrent technique was used to measure this Vbi, which systematically improves with diode structure.
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85.60.Jb Light-emitting devices
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
FREE

Magnetoelectroluminescence in tris (8-hydroxyquinolato) aluminum-based organic light-emitting diodes doped with fluorescent dyes

P. Chen, Y. L. Lei, Q. L. Song, Y. Zhang, R. Liu, Q. M. Zhang, and Z. H. Xiong

Appl. Phys. Lett. 95, 213304 (2009); http://dx.doi.org/10.1063/1.3266844 (3 pages) | Cited 9 times

Online Publication Date: 25 November 2009

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The influences of fluorescent dye doping on the magnetoelectroluminescence in tris (8-hydroxyquinolato) aluminum (Alq3)-based organic light-emitting diodes have been investigated systematically by varying the dopant concentrations and its energy band gap. Our results show that the decrease in electroluminescence intensity at high magnetic field, which survives only at low temperatures for pure Alq3-based devices, persists in dye-doped devices even at room temperature. This is explained here as the result of magnetic field dependent triplet-triplet annihilation process, in which the triplet excitons trapped on the dye molecules play the most important role.
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85.60.Jb Light-emitting devices
FREE

Highly efficient yellow organic light emitting diode based on a layer-cross faded emission layer allowing easy color tuning

Florian Lindla, Manuel Boesing, Christoph Zimmermann, Frank Jessen, Philipp van Gemmern, Dietrich Bertram, Dietmar Keiper, Nico Meyer, Michael Heuken, Holger Kalisch, and Rolf H. Jansen

Appl. Phys. Lett. 95, 213305 (2009); http://dx.doi.org/10.1063/1.3266849 (3 pages) | Cited 12 times

Online Publication Date: 25 November 2009

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An easy way to adjust the color of yellow organic light emitting diodes (OLED) is realized by basing the emission layer on a cross-fading zone of two unipolar-conducting host materials doping parts of it either with a red or green phosphorescent emitter at varying thickness ratios. At color coordinates of 0.47/0.50, a current efficacy of 42.2 cd/A (16.2% external quantum efficiency) and a power efficacy of 32.9 lm/W (1000 cd/m2) are measured without light extraction enhancement. Mixed-host emission layer OLED without cross-fading are processed for comparison. Exciton distributions are studied. The concept is suggested to be useful for white OLED.
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85.60.Jb Light-emitting devices
FREE

Efficient semitransparent small-molecule organic solar cells

Jan Meiss, Karl Leo, Moritz K. Riede, Christian Uhrich, Wolf-Michael Gnehr, Stefan Sonntag, and Martin Pfeiffer

Appl. Phys. Lett. 95, 213306 (2009); http://dx.doi.org/10.1063/1.3268784 (3 pages) | Cited 13 times

Online Publication Date: 25 November 2009

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We present semitransparent small-molecule organic solar cells (OSC) deposited by thermal evaporation onto indium tin oxide (ITO)-coated glass substrates. The devices employ ITO-free ultrathin metal layers as top electrodes, containing 1 nm metal surfactant interlayer for improved morphology. Using a bulk heterojunction of zinc phthalocyanine and C60, sandwiched in between doped dedicated transport layers for efficient charge carrier extraction, power conversion efficiencies comparable to conventional OSC with an intransparent thick back electrode and similar device layout are achieved: the semitransparent OSC yield power conversion efficiencies well above 2% with external quantum efficiencies above 30%–40%. Organic light incoupling layers improve the transmission to up to 50% in the visible part of the optical spectrum.
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88.40.jr Organic photovoltaics
81.15.Dj E-beam and hot filament evaporation deposition
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.40.-q Absorption and reflection spectra: visible and ultraviolet
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Enhancement of electrical property by oxygen doping to copper phthalocyanine in inverted top emitting organic light emitting diodes

Kihyon Hong, Kisoo Kim, and Jong-Lam Lee

Appl. Phys. Lett. 95, 213307 (2009); http://dx.doi.org/10.1063/1.3266856 (3 pages) | Cited 13 times

Online Publication Date: 25 November 2009

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We reported the evidence of oxygen doping to copper-phthalocyanine (CuPc) by O2-plasma treatment to inverted top-emitting organic light-emitting diodes (ITOLEDs). In situ synchrotron-radiation photoelectron spectroscopy results showed that a new Cu–O bond appeared and the energy difference between the highest-occupied molecular orbital and EF is lowered by 0.15 eV after plasma treatment. The oxygen ions chemically interacted with Cu atoms and transferred charges to the CuPc. Thus the hole injection barrier was lowered, enhancing the electroluminescent property of ITOLEDs.
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85.60.Jb Light-emitting devices
85.40.Ry Impurity doping, diffusion and ion implantation technology
41.60.Ap Synchrotron radiation
78.60.Fi Electroluminescence
FREE

Increasing organic vertical carrier mobility for the application of high speed bilayered organic photodetector

Wu-Wei Tsai, Yu-Chiang Chao, En-Chen Chen, Hsiao-Wen Zan, Hsin-Fei Meng, and Chain-Shu Hsu

Appl. Phys. Lett. 95, 213308 (2009); http://dx.doi.org/10.1063/1.3263144 (3 pages) | Cited 4 times

Online Publication Date: 25 November 2009

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The direct influence of the vertical carrier mobility on the frequency response of bilayered organic photodiodes (PDs) is investigated for the first time. With fullerene as the acceptor material, changing vertical hole mobility from 2.3×10−5 to 2.8×10−4 cm2/V s increases PD bandwidth from 10 to 80 MHz under a 4 V operation. The influence of deposition rate on vertical hole mobility of pentacene film is also discussed. Our results facilitate the application of bilayered organic PDs on the detection of very-high-frequency optical signals.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors
73.50.Dn Low-field transport and mobility; piezoresistance
73.61.Ph Polymers; organic compounds
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Wide dynamic range terahertz detector pixel for active spectroscopic imaging with quantum cascade lasers

S. Cibella, M. Ortolani, R. Leoni, G. Torrioli, L. Mahler, Ji-Hua Xu, A. Tredicucci, H. E. Beere, and D. A. Ritchie

Appl. Phys. Lett. 95, 213501 (2009); http://dx.doi.org/10.1063/1.3265958 (3 pages) | Cited 5 times

Online Publication Date: 23 November 2009

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A superconducting bolometer with an on-chip lithographic terahertz antenna has been illuminated by two quantum cascade lasers operating at 2.5 and 4.4 THz. The detector displays a 1.2 μs time constant, a noise equivalent power of 20 fW/Hz1/2 and a 60 dB dynamic range. We fabricated a monolithic prototype detector array of five elements. This scalable detector is a suitable candidate for terahertz spectroscopic imaging systems, as it can measure both full illuminator power and strongly attenuated or diffuse reflected signals in subsequent frames.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.60.By Design of specific laser systems
85.25.-j Superconducting devices

Recombination mechanisms in highly efficient thin film Zn(S,O)/Cu(In,Ga)S2 based solar cells

S. Merdes, R. Sáez-Araoz, A. Ennaoui, J. Klaer, M. Ch. Lux-Steiner, and R. Klenk

Appl. Phys. Lett. 95, 213502 (2009); http://dx.doi.org/10.1063/1.3266829 (3 pages) | Cited 11 times

Online Publication Date: 24 November 2009

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Progress in fabricating Cu(In,Ga)S2 based solar cells with Zn(S,O) buffer is presented. An efficiency of 12.9% was achieved. Using spectral response, current-voltage and temperature dependent current-voltage measurements, current transport in this junction was studied and compared to that of a highly efficient CdS/Cu(In,Ga)S2 solar cell with a special focus on recombination mechanisms. Independently of the buffer type and despite the difference in band alignment of the two junctions, interface recombination is found to be the main recombination channel in both cases. This was unexpected since it is generally assumed that a cliff facilitates interface recombination while a spike suppresses it.
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88.40.hj Efficiency and performance of solar cells
88.40.jn Thin film Cu-based I-III-VI2 solar cells
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.25.+i Surface conductivity and carrier phenomena

Analog memory capacitor based on field-configurable ion-doped polymers

Qianxi Lai, Lei Zhang, Zhiyong Li, William F. Stickle, R. Stanley Williams, and Yong Chen

Appl. Phys. Lett. 95, 213503 (2009); http://dx.doi.org/10.1063/1.3268433 (3 pages) | Cited 3 times

Online Publication Date: 25 November 2009

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A memory capacitor based on a field-configurable ion-doped polymer is reported. The device can be dynamically and reversibly programed to analog capacitances with low-voltage (<5 V) pulses. After the device is programed to a specific value, its capacitance remains nonvolatile. The field-configurable capacitance is attributed to the modification of ionic dopant concentrations in the polymer. The memory capacitors might be used for analog memory, nonlinear analog, and neuromorphic circuits.
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84.32.Tt Capacitors
84.30.Sk Pulse and digital circuits
85.40.Ry Impurity doping, diffusion and ion implantation technology
73.61.Ph Polymers; organic compounds

Suppression of ambipolar behavior in metallic source/drain metal-oxide-semiconductor field-effect transistors

H. Ghoneim, J. Knoch, H. Riel, D. Webb, M. T. Björk, S. Karg, E. Lörtscher, H. Schmid, and W. Riess

Appl. Phys. Lett. 95, 213504 (2009); http://dx.doi.org/10.1063/1.3266526 (3 pages) | Cited 1 time

Online Publication Date: 25 November 2009

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We present a study on suppressing the ambipolar behavior of Schottky barrier metal-oxide-semiconductor field-effect transistors (MOSFET). Inserting a silicon nitride layer of appropriate thickness between the metallic source/drain electrodes and the silicon yields a low Schottky-barrier and simultaneously tunes the properties of the contact from metal-semiconductor-like to the behavior of a doped contact. Moreover, device characteristics of pseudo-MOSFETs reveal an efficient suppression of ambipolar behavior. Comparison with an alternative way of achieving low Schottky-barrier contacts, i.e., by inserting a strong dipole layer such as LiF between the metal and the silicon, reveals that the suppression is not a result of shifting the Fermi level closer to the conduction band but is caused by a reduction of metal-induced gap states. The trade-off between suppression of the ambipolar behavior, contact length and on-state current is investigated with simulations.
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85.30.Tv Field effect devices
89.20.Kk Engineering

Thermal flying-height control sliders in hard disk drives filled with air-helium gas mixtures

Nan Liu, Jinglin Zheng, and David B. Bogy

Appl. Phys. Lett. 95, 213505 (2009); http://dx.doi.org/10.1063/1.3268468 (3 pages) | Cited 1 time

Online Publication Date: 25 November 2009

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This letter employs established approaches to calculate the physical properties of the air-helium gas mixtures and investigates the thermal flying-height control slider’s flying performance in these environments. It is found that at a fixed heater power, the slider’s flying height first increases and then decreases with the fraction of helium in the gas mixture due to the combined effects of changes in the mean free path, viscosity, and thermal conductivity of the gas mixture with helium content. These findings, together with the proposed approach, are useful for future designs of sliders in air-helium mixtures.
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85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
89.20.Kk Engineering

Improved performance of poly(3-hexylthiophene)/zinc oxide hybrid photovoltaics modified with interfacial nanocrystalline cadmium sulfide

Erik D. Spoerke, Matthew T. Lloyd, Erica M. McCready, Dana C. Olson, Yun-Ju Lee, and Julia W. P. Hsu

Appl. Phys. Lett. 95, 213506 (2009); http://dx.doi.org/10.1063/1.3232231 (3 pages) | Cited 24 times

Online Publication Date: 25 November 2009

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To improve zinc oxide/poly(3-hexylthiophene) (ZnO/P3HT) hybrid solar cell performance, we introduce a nanocrystalline cadmium sulfide (CdS) film at the ZnO/P3HT heterojunction, creating a cascading energy band structure. Current-voltage characteristics under AM1.5 illumination show that, compared to unmodified ZnO/P3HT devices, CdS modification leads to an approximate doubling of the open-circuit voltage and a mild increase in fill factor, without sacrificing any short-circuit current. These characteristics double the power conversion efficiency for devices with an interfacial CdS layer. External quantum efficiency spectra reveal definite photocurrent contributions from the CdS layer, confirming the cascading band structure. The mechanisms behind open-circuit voltage increase are discussed.
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84.60.Jt Photoelectric conversion
73.20.At Surface states, band structure, electron density of states
72.40.+w Photoconduction and photovoltaic effects
81.05.Dz II-VI semiconductors
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
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