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28 Nov 2011

Volume 99, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 221902 (2011); http://dx.doi.org/10.1063/1.3663578 (3 pages)

Aparna Deshpande, Kai Felix Braun, and Saw-Wai Hla
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The origin of athermal training in polycrystalline metallic exchange bias thin films

B. Kaeswurm and K. O’Grady

Appl. Phys. Lett. 99, 222508 (2011); http://dx.doi.org/10.1063/1.3661172 (3 pages) | Cited 2 times

Online Publication Date: 29 November 2011

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The phenomenon of training in exchange bias systems has no clear and unambiguous explanation. It is known that the training effect consists of an athermal and a thermal component where the latter derives from the well understood thermal instability in the bulk of the antiferromagnetic (AF) grains. In this work, we report on a study of the magnetic properties of a tri-layer system consisting of F/AF/F where reversal of the individual ferromagnetic (F) layers shows that the athermal training effect derives solely from the interface spin configuration and not from the bulk of the AF grains. We propose a model whereby the origin of the training derives from the degree of order in interfacial spin clusters which lie in a thermo-remanent state after the AF is set and whose order is disrupted by the application of a reverse field resulting in a reduced coercivity and the characteristic change in the loop shape.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Ds Spin waves
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Modeling of spin-torque driven magnetization dynamics in a spin-valve with combined in-plane and out-of-plane polarizers

Zhiwei Hou, Zongzhi Zhang, Jianwei Zhang, and Yaowen Liu

Appl. Phys. Lett. 99, 222509 (2011); http://dx.doi.org/10.1063/1.3664113 (3 pages) | Cited 5 times

Online Publication Date: 29 November 2011

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Spin-torque (ST) driven magnetization dynamics have been investigated in a spin-valve structure that consists of an in-plane (IP) free layer and two fixed polarizers [magnetized IP and out-of-plane (OP)]. Three distinct dynamics including no switching, switching, and periodic oscillation are identified in a phase diagram governed by the ST parameters. The ST strengths which are able to switch the free layer have been analytically predicted and supported by simulations, showing that the torque originated from the OP polarizer should be much smaller than that from the IP polarizer. The free layer driven by the dual polarizers could switch 10 times faster than that by a single IP polarizer.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.78.-n Magnetization dynamics
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Tuning the magnetism of the Heusler alloys Mn3−xCoxGa from soft and half-metallic to hard-magnetic for spin-transfer torque applications

Vajiheh Alijani, Juergen Winterlik, Gerhard H. Fecher, and Claudia Felser

Appl. Phys. Lett. 99, 222510 (2011); http://dx.doi.org/10.1063/1.3665260 (3 pages) | Cited 10 times

Online Publication Date: 30 November 2011

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The magnetic properties of Mn3−xCoxGa Heusler alloys exhibit a very interesting feature. While the Mn-rich alloys (x = 0.1−0.4) are similar to Mn3Ga as they crystallize in a tetragonally distorted variation of the Heusler structure and exhibit comparable hard-ferrimagnetic properties highly useful for spin-transfer torque applications, the Co-rich samples (x = 0.6–1) exhibit cubic Heusler structures, have soft-magnetic hysteresis loops, and follow the generalized Slater-Pauling curve indicating half-metallic ferrimagnetism. The Curie temperatures of all alloys are above 700 K allowing for high operating temperatures.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Gg Ferrimagnetics

Polaronic transport and magnetism in Ag-doped ZnO

M. He, Y. F. Tian, D. Springer, I. A. Putra, G. Z. Xing, E. E. M. Chia, S. A. Cheong, and T. Wu

Appl. Phys. Lett. 99, 222511 (2011); http://dx.doi.org/10.1063/1.3665401 (3 pages) | Cited 10 times

Online Publication Date: 30 November 2011

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Magnetic polarons have been proposed to play important roles in doped wide band gap oxides that exhibit weak room temperature ferromagnetism. Here, we report the experimental evidence supporting polaronic magnetism and transport in Ag-doped ZnO. Temperature dependent resistivity data suggest the conduction mechanism of Mott and Efros variable range hopping. The observed weak ferromagnetism and its temperature dependence are explained using the percolation-based model of partially ordered bound magnetic polarons.
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72.20.Ee Mobility edges; hopping transport
71.38.-k Polarons and electron-phonon interactions
75.50.Pp Magnetic semiconductors
72.80.Ey III-V and II-VI semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Local structure and magnetic properties of Mn-doped 3C-SiC nanoparticles

H. W. Zheng, Z. Q. Wang, X. Y. Liu, C. L. Diao, H. R. Zhang, and Y. Z. Gu

Appl. Phys. Lett. 99, 222512 (2011); http://dx.doi.org/10.1063/1.3665258 (3 pages) | Cited 5 times

Online Publication Date: 1 December 2011

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Mn-doped 3C-SiC nanoparticles have been fabricated by a sol-gel and carbothermal reduction method. The average particle size of the nanoparticles is about 126 nm. Raman scattering studies indicate that the transverse optical and the longitudinal optical modes shift to low wave number and the full widths at half-maximum of Raman peaks increase after Mn was doped. Extended x-ray absorption fine structure reveals that the doped-Mn atoms substitute for the C sites in the 3C-SiC lattice. Magnetic measurement results show that the room temperature intrinsic ferromagnetism (FM) order is established. The origin of the FM has been discussed in detail.
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81.16.-c Methods of micro- and nanofabrication and processing
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
75.50.Dd Nonmetallic ferromagnetic materials
78.30.Hv Other nonmetallic inorganics
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
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Phase transition sequence in sodium bismuth titanate observed using high-resolution x-ray diffraction

Elena Aksel, Jennifer S. Forrester, Benjamin Kowalski, Jacob L. Jones, and Pam A. Thomas

Appl. Phys. Lett. 99, 222901 (2011); http://dx.doi.org/10.1063/1.3664393 (3 pages) | Cited 11 times

Online Publication Date: 28 November 2011

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High resolution powder x-ray diffraction patterns of Na0.5Bi0.5TiO3 at selected temperatures were examined to compare structural changes with observed piezoelectric thermal depoling temperatures. The depoling temperatures do not correlate with discrete phase transition temperatures, and therefore, a structural transition is not the origin of thermal depoling. Rather, a correlation is made with an increase in volume fraction of material which does not obey the long-range Cc space group. The origin of the thermal depoling behavior may be the loss of long-range ferroelectric order by a decreasing proportion of the Cc phase or the associated percolation of disordered nano-scale platelets.
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64.70.K- Solid-solid transitions
77.65.-j Piezoelectricity and electromechanical effects
77.80.B- Phase transitions and Curie point

Influence of strain on the electronic structure of the TbMnO3/SrTiO3 epitaxial interface

S. Venkatesan, M. Döblinger, C. Daumont, B. Kooi, B. Noheda, J. T. M. De Hosson, and C. Scheu

Appl. Phys. Lett. 99, 222902 (2011); http://dx.doi.org/10.1063/1.3663218 (3 pages)

Online Publication Date: 29 November 2011

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Understanding the magnetotransport properties of epitaxial strained thin films requires knowledge of the chemistry at the interface. We report on the change in Mn electronic structure at the epitaxially strained TbMnO3/SrTiO3 interface. Scanning transmission electron microscopy shows an abrupt interface with a bright contrast, indicating the presence of misfit strain. Electron energy loss spectroscopy displays a chemical shift of the Mn L2,3 edge together with a high white line intensity ratio revealing a reduction in the nominal Mn oxidation state in the first 3–4 monolayers. These observations indicate misfit strain significantly changes the electronic structure at the interface.
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77.55.Nv Multiferroic/magnetoelectric films
77.80.bn Strain and interface effects
77.84.Cg PZT ceramics and other titanates
72.20.My Galvanomagnetic and other magnetotransport effects

Suppression of dielectric crystallization on metal by introduction of SiO2 layer for metal floating gate memory blocking oxide

Srikant Jayanti and Veena Misra

Appl. Phys. Lett. 99, 222903 (2011); http://dx.doi.org/10.1063/1.3661173 (3 pages)

Online Publication Date: 29 November 2011

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A technique of reducing the higher degree of dielectric crystallization on polycrystalline metal has been investigated by inserting a thin SiO2 layer interfacing the metal for application as high-k blocking oxide in metal floating gate FLASH memories. Grazing incidence x-ray diffraction study showed that the insertion of an amorphous interfacial layer (IL) suppresses the crystallization of HfAlO blocking oxide considerably. The electrical performance of the blocking oxide stacks was characterized using metal-insulator-metal capacitors, and the thermal stability was observed to improve by more than an order of magnitude with the incorporation of SiO2 IL.
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73.40.Rw Metal-insulator-metal structures
77.22.Ch Permittivity (dielectric function)
77.55.D- High-permittivity gate dielectric films
61.43.-j Disordered solids

Domain structure and in-plane switching in a highly strained Bi0.9Sm0.1FeO3 film

Weigang Chen, Wei Ren, Lu You, Yurong Yang, Zuhuang Chen, Yajun Qi, Xi Zou, Junling Wang, Thirumany Sritharan, Ping Yang, L. Bellaiche, and Lang Chen

Appl. Phys. Lett. 99, 222904 (2011); http://dx.doi.org/10.1063/1.3664394 (3 pages) | Cited 2 times

Online Publication Date: 29 November 2011

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We report the domain structure and ferroelectric properties of a 32 nm-thick Bi0.9Sm0.1FeO3 film epitaxially grown on a LaAlO3 (LAO) substrate. This film exhibits a monoclinic Mc phase, with its monoclinic distortion and anisotropy of in-plane (IP) lattice parameters being both smaller than those of pure BiFeO3 (BFO) grown on LaAlO3. Polarization hysteresis loops measured using a quasi-planar capacitor show an in-plane polarization up to 30 μC/cm2. Piezoresponse force microcopy demonstrates that a 180° in-plane polarization switching accompanied by a 90° domain wall rotation takes place after electric poling. First-principles calculations suggest the differences between highly strained Sm-substituted and pure BiFeO3.
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77.55.Nv Multiferroic/magnetoelectric films
75.85.+t Magnetoelectric effects, multiferroics
77.80.Fm Switching phenomena
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization

Reduction of leakage currents with nanocrystals embedded in an amorphous matrix in metal-insulator-metal capacitor stacks

A. Krause, W. M. Weber, U. Schröder, D. Pohl, B. Rellinghaus, J. Heitmann, and T. Mikolajick

Appl. Phys. Lett. 99, 222905 (2011); http://dx.doi.org/10.1063/1.3664395 (3 pages)

Online Publication Date: 29 November 2011

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CaTiO3 layers with varying thicknesses in metal-insulator-metal capacitor stacks were deposited at 550 °C using radio-frequency magnetron sputtering. The combination of electrical and transmission electron microscopy measurements allows a correlation of k-value and leakage current to the degree of crystallinity. Experiments show that higher crystallinity and, therefore, higher k-values lead to increasing leakage currents and change of conduction mechanisms. However, leakage currents are significantly reduced when crystallites are embedded in an amorphous matrix. Selective growth of these crystallites is owed to cube-on-cube nucleation of CaTiO3 on {011} Pt.
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84.32.Tt Capacitors
85.40.Sz Deposition technology
81.15.Cd Deposition by sputtering

Bonding principles of passivation mechanism at III-V-oxide interfaces

J. Robertson and L. Lin

Appl. Phys. Lett. 99, 222906 (2011); http://dx.doi.org/10.1063/1.3665061 (3 pages) | Cited 10 times

Online Publication Date: 30 November 2011

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We analyze the conditions necessary to passivate interfacial defects at III-V-oxide interfaces, in terms of an electron-counting rule. We propose that this rule, previously used to describe reconstructions at GaAs or ZnSe surfaces, acts during oxide growth or deposition, atomic layer by atomic layer. The need to satisfy this rule continuously drives the creation of interface defects, whose states can lie in the bulk band gap of the semiconductor.
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81.65.Rv Passivation
73.20.At Surface states, band structure, electron density of states
81.05.Ea III-V semiconductors
71.55.Eq III-V semiconductors

Interface composition of InAs nanowires with Al2O3 and HfO2 thin films

R. Timm, M. Hjort, A. Fian, B. M. Borg, C. Thelander, J. N. Andersen, L.-E. Wernersson, and A. Mikkelsen

Appl. Phys. Lett. 99, 222907 (2011); http://dx.doi.org/10.1063/1.3664399 (3 pages) | Cited 4 times

Online Publication Date: 30 November 2011

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Vertical InAs nanowires (NWs) wrapped by a thin high-κ dielectric layer may be a key to the next generation of high-speed metal-oxide-semiconductor devices. Here, we have investigated the structure and chemical composition of the interface between InAs NWs and 2 nm thick Al2O3 and HfO2 films. The native oxide on the NWs is significantly reduced upon high-κ deposition, although less effective than for corresponding planar samples, resulting in a 0.8 nm thick interface layer with an In-/As-oxide composition of about 0.7/0.3. The exact oxide reduction and composition including As-suboxides and the role of the NW geometry are discussed in detail.
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68.65.La Quantum wires (patterned in quantum wells)
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
77.55.D- High-permittivity gate dielectric films
81.07.Bc Nanocrystalline materials
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Magnetic properties of Sr2FeTaO6 double perovskite epitaxially grown by pulsed-laser deposition

S. Chakraverty, M. Saito, S. Tsukimoto, Y. Ikuhara, A. Ohtomo, and M. Kawasaki

Appl. Phys. Lett. 99, 223101 (2011); http://dx.doi.org/10.1063/1.3663214 (3 pages) | Cited 1 time

Online Publication Date: 28 November 2011

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We have investigated the magnetic properties of B-site-ordered Sr2FeTaO6 double perovskite thin films grown on (111) SrTiO3 substrates by using pulsed-laser deposition. High degree of ordering of Fe and Ta ions has been confirmed using x-ray diffraction and atomically resolved high-angle annular dark-field scanning transmission electron microscopy. We have found clear signatures of magnetic frustration in {111} planes of local spin moment arising from next-nearest-neighbor interaction in triangular FeO6 sublattice below 50 K. It is also found that this behavior is suppressed by increasing disorder and eventually leads to antiferromagnetic state.
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77.55.Px Epitaxial and superlattice films
75.70.-i Magnetic properties of thin films, surfaces, and interfaces
68.55.A- Nucleation and growth
81.15.Fg Pulsed laser ablation deposition

Low-temperature graphene growth using epochal catalyst of PdCo alloy

Eun Sung Kim, Hyeon-Jin Shin, Seon-Mi Yoon, Gang Hee Han, Seung Jin Chae, Jung Jun Bae, Fethullah Gunes, Jae-Young Choi, and Young Hee Lee

Appl. Phys. Lett. 99, 223102 (2011); http://dx.doi.org/10.1063/1.3665616 (3 pages) | Cited 4 times

Online Publication Date: 30 November 2011

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Palladium-Cobalt alloy as a catalyst was introduced to realize low temperature graphene growth on glass substrate by using remote RF plasma-enhanced chemical vapor deposition. Few layer graphene films were easily formed with high transmittance of 88.8% at temperature as low as 400 °C, in good contrast with Ni catalyst in which no graphitic layer was formed at all at the same conditions. High decomposition rate of hydrocarbon gases and formation of nanosize aggregates giving rise to enhancement of carbon incorporation into PdCo alloy and consequently formation of graphene layers at such low temperatures are further discussed with observed Raman spectroscopy and x-ray diffraction.
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81.05.ue Graphene
78.30.Na Fullerenes and related materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Periodic oscillation of photocurrents in single-walled carbon nanotubes

Daisuke Hirai and Satoru Konabe

Appl. Phys. Lett. 99, 223103 (2011); http://dx.doi.org/10.1063/1.3664128 (3 pages) | Cited 1 time

Online Publication Date: 30 November 2011

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We perform a theoretical study of photocurrent of semiconducting single-walled carbon nanotubes (s-SWNTs) with lengths of the order of sub micrometers using the Keldysh nonequilibrium Green’s function method. We found that photocurrents in s-SWNTs exhibit periodic oscillations (i.e., the resistance varies periodically) as a function of length of the laser-irradiated region. To interpret this oscillating behavior, we derive the analytical expression for the photocurrent in the effective mass approximation.
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72.40.+w Photoconduction and photovoltaic effects
02.30.-f Function theory, analysis
78.66.Db Elemental semiconductors and insulators
73.61.Cw Elemental semiconductors
78.67.Ch Nanotubes

Growth of [010] oriented α-MoO3 nanorods by pulsed electron beam deposition

Can Liu, Zhengcao Li, and Zhengjun Zhang

Appl. Phys. Lett. 99, 223104 (2011); http://dx.doi.org/10.1063/1.3664779 (3 pages)

Online Publication Date: 30 November 2011

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Arrays of vertically aligned, [010] oriented α-MoO3 nanorods were grown on planar silicon substrates by pulsed electron beam deposition. The morphology and structure of the nanorods as well as their growth mechanism were investigated. These [010] oriented nanorods exhibited a good field emission performance with a turn-on field of 3.6 V/μm. As the space between layers of the [010] oriented nanorods is large, their formation may be also meaningful for exploring the gas sensing and energy storage properties of layered oxides like α-MoO3.
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81.16.-c Methods of micro- and nanofabrication and processing
81.15.Jj Ion and electron beam-assisted deposition; ion plating
79.70.+q Field emission, ionization, evaporation, and desorption
61.66.Fn Inorganic compounds

Fabrication of large-area ultra-thin single crystal silicon membranes

Z. Y. Dang, M. Motapothula, Y. S. Ow, T. Venkatesan, M. B. H. Breese, M. A. Rana, and A. Osman

Appl. Phys. Lett. 99, 223105 (2011); http://dx.doi.org/10.1063/1.3665620 (3 pages) | Cited 5 times

Online Publication Date: 1 December 2011

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Perfectly, crystalline, 55 nm thick silicon membranes have been fabricated over several square millimeters and used to observe transmission ion channeling patterns showing the early evolution of the axially channeled beam angular distribution for small tilts away from the [011] axis. The reduced multiple scattering through such thin layers allows fine angular structure produced by the highly non-equilibrium transverse momentum distribution of the channeled beam during its initial propagation in the crystal to be resolved. The membrane crystallinity and flatness were measured by using proton channeling measurements and the surface roughness of 0.4 nm using atomic force microscopy.
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81.16.Rf Micro- and nanoscale pattern formation
68.35.bg Semiconductors
68.55.ag Semiconductors
61.85.+p Channeling phenomena (blocking, energy loss, etc.)

Built-in field reduction in InGaN/GaN quantum dot molecules

S. Schulz and E. P. O’Reilly

Appl. Phys. Lett. 99, 223106 (2011); http://dx.doi.org/10.1063/1.3665069 (3 pages) | Cited 1 time

Online Publication Date: 2 December 2011

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We use a tight-binding model to study the electronic structure of InGaN/GaN quantum dot molecules grown along the c-axis. This analysis is carried out as a function of the barrier thickness between the two non-identical dots. Our results show that the built-in field is effectively reduced in systems of coupled nitride quantum dots, leading to an increased spatial overlap of electron and hole wave functions compared to an isolated dot. This finding is in agreement with experimental data reported in the literature and is directly related to the behavior of the built-in potential outside an isolated dot.
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71.20.Nr Semiconductor compounds
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

Vapor-liquid-solid growth of Ge nanowhiskers enhanced by high-temperature glancing angle deposition

Motofumi Suzuki, Kenji Hamachi, Hideki Hara, Kaoru Nakajima, Kenji Kimura, Chia-Wei Hsu, and Li-Jen Chou

Appl. Phys. Lett. 99, 223107 (2011); http://dx.doi.org/10.1063/1.3664777 (3 pages) | Cited 3 times

Online Publication Date: 2 December 2011

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We have demonstrated that the vapor-liquid-solid (VLS) growth of Ge nanowhiskers is significantly enhanced by high-temperature glancing angle deposition (HT-GLAD). At the substrate temperature of 420 °C, the Ge nanowhiskers grow on the sample deposited at the deposition angle of α = 85°, whereas no long nanowhisker grows on the samples deposited at α ≤ 73°. The kinetic growth model that takes into account the directional incidence of the vapor flux agrees with the experimental results and suggests that the atoms deposited on the side surface of the nanowhiskers play an essential role in the HT-GLAD assisted VLS growth. Supplying the atoms on the side surface of the nanowhiskers is expected to accelerate the growth of the nanowhiskers in any vapor phase growth methods, such as molecular beam epitaxy and chemical vapor deposition.
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81.07.Gf Nanowires
68.47.Fg Semiconductor surfaces
81.05.Cy Elemental semiconductors
68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
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Solid-state nuclear magnetic resonance analysis of phase separation behavior of regioregular poly(3-hexylthiophene) and [6,6]-phenyl-C61-butyric acid methyl ester in bulk heterojunction organic solar cells

Tatsuya Fukushima, Hironobu Kimura, Yurie Shimahara, and Hironori Kaji

Appl. Phys. Lett. 99, 223301 (2011); http://dx.doi.org/10.1063/1.3662854 (3 pages) | Cited 1 time

Online Publication Date: 30 November 2011

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The origin of the improvement in power conversion efficiency (PCE) by the thermal annealing of bulk heterojunction organic solar cells, based on regioregular poly(3-hexylthiophene-2,5-diyl) (rrP3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), is analyzed via solid-state nuclear magnetic resonance (NMR). 1H spin-lattice relaxation experiments of solid-state NMR clearly reveal that the phase-separated heterojunction structure develops on the order of several tens of nanometers in rrP3HT/PCBM blend films with thermal annealing at 150 °C. The development of the phase-separated structure explains the increase in the PCE for the solar cell system from 0.7% to nearly 3% through the thermal annealing.
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88.40.jr Organic photovoltaics
88.40.hj Efficiency and performance of solar cells
FREE

Polymer solar cells with gold nanoclusters decorated multi-layer graphene as transparent electrode

Di Zhang, Wallace C. H. Choy, Charlie C. D. Wang, Xiao Li, Lili Fan, Kunlin Wang, and Hongwei Zhu

Appl. Phys. Lett. 99, 223302 (2011); http://dx.doi.org/10.1063/1.3664120 (3 pages) | Cited 6 times

Online Publication Date: 30 November 2011

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A thin layer of ultraviolet-ozone (UVO) treated gold (Au) is introduced on multi-layer graphene (MLG) to enable the MLG as an effective anode for polymer solar cells (PSCs). By optimizing the Au thickness and the durations of the UVO treatments at different stages, MLG PSCs with enhanced fill factor and power conversion efficiency are obtained, exhibiting better performance compared with MLG devices directly modified with UVO and poly(3,4-ethylenedioythiophene):poly(styrenesulfonate). Further analysis shows that UVO treated Au provides favorable band alignment at the MLG/polymer interface. Moreover, the improved interfacial contact and shortened UVO durations reduce the series resistance of PSCs significantly.
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88.40.H- Solar cells (photovoltaics)
61.41.+e Polymers, elastomers, and plastics
82.45.Fk Electrodes
61.48.Gh Structure of graphene
88.40.J- Types of solar cells
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Enhanced efficiency in high-brightness fluorescent organic light emitting diodes through triplet management

Yifan Zhang, Michael Slootsky, and Stephen R. Forrest

Appl. Phys. Lett. 99, 223303 (2011); http://dx.doi.org/10.1063/1.3664771 (3 pages) | Cited 1 time

Online Publication Date: 30 November 2011

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We demonstrate suppressed singlet-triplet (S-T) quenching, and hence increased quantum efficiency, in high-brightness fluorescent organic light emitting diodes (OLEDs) by reducing the guest triplet population through the introduction of a triplet manager molecule into the emission layer (EML). As an example, an OLED whose EML consists of the red fluorophore, 4-(dicyanomethylene)-2-methyl-6-julolidyl-9-enyl-4H-pyran doped into the host, tris(8-hydroxyquinoline) Al (Alq3) is blended with the triplet manager, 9,10-di(naphtha-2-yl)anthracene. The manager triplet energy is less than that of the host or dopant, leading to efficient triplet removal from the dopant without affecting the radiative singlet population. Measurements suggest the complete suppression of S-T quenching using the triplet management strategy, leading to >100% increase in the steady-state OLED external quantum efficiency.
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85.60.Jb Light-emitting devices
FREE

Demonstration of interfacial charge transfer in an organic charge injection device

C. P. Watson and D. M. Taylor

Appl. Phys. Lett. 99, 223304 (2011); http://dx.doi.org/10.1063/1.3665190 (3 pages) | Cited 1 time

Online Publication Date: 1 December 2011

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We report the fabrication and testing of an organic charge injection device composed of two adjacent metal-insulator-semiconductor capacitors in which the active semiconductor is poly(3-hexylthiophene). One capacitor, C1, is biased into partial depletion and illuminated with 550 nm light. By applying higher depletion voltages to the second capacitor, C2, photogenerated electrons are induced to flow along the semiconductor-insulator interface from C1 to C2 where they are detected either by simultaneously measuring the C-V characteristic of C2 or the current flow into it. We estimate that the transfer efficiency is in excess of 40% but is capable of significant improvement.
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84.32.Tt Capacitors
FREE

Improving the efficiency of an organic solar cell by a polymer additive to optimize the charge carriers mobility

Ming-Chung Chen, Der-Jang Liaw, Wen-Hsiang Chen, Ying-Chi Huang, Jadab Sharma, and Yian Tai

Appl. Phys. Lett. 99, 223305 (2011); http://dx.doi.org/10.1063/1.3664127 (3 pages) | Cited 5 times

Online Publication Date: 1 December 2011

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We investigate the effect of a high hole mobility triarylamine-based conjugated polymer on a bulk hetero-junction organic solar cell. We employed a polymer blend consisting of poly(3-hexylthiophene) (P3HT), [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), and poly(N-(4 -(9,9-dioctyl-fluoren-2-yl)phenyl)-N,N′,N′-triphenyl-l,4-phenylenediamine) (PFLAM) as active materials. The hole mobility of PFLAM is ∼10−3 cm2 V−1 s−1, which is similar to the electron mobility of PCBM. Addition of PFLAM improves the hole mobility of the photovoltaic cell augmenting the charge balance of the system. The overall efficiency gain for such a device is 34%.
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88.40.hj Efficiency and performance of solar cells
88.40.jr Organic photovoltaics
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Influence of threading dislocation density on early degradation in AlGaN/GaN high electron mobility transistors

M. Ťapajna, S. W. Kaun, M. H. Wong, F. Gao, T. Palacios, U. K. Mishra, J. S. Speck, and M. Kuball

Appl. Phys. Lett. 99, 223501 (2011); http://dx.doi.org/10.1063/1.3663573 (3 pages) | Cited 7 times

Online Publication Date: 28 November 2011

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Early stage degradation of AlGaN/GaN high electron mobility transistors (HEMTs) with different threading dislocation densities (TDDs) submitted to off-state voltage bias stress was studied. It was found that, for the stress conditions used, HEMTs with TDD ∼1010 cm−2 show pronounced degradation in terms of maximum drain current, gate-lag, and trap generation measured by drain current trapping characteristics, a slight degradation in gate leakage was observed also for HEMTs with TDD of ∼108 cm−2, and no significant degradation for devices with TDD in the ∼107 cm−2 range. The results illustrate the importance of TDD for degradation and reliability of AlGaN/GaN HEMTs.
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85.30.Tv Field effect devices
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