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9 Oct 2006

Volume 89, Issue 15, Articles (15xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 89, 151920 (2006); http://dx.doi.org/10.1063/1.2360906 (3 pages)

Aycan Yurtsever, Matthew Weyland, and David A. Muller
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Enhanced performance of white polymer light-emitting diodes using polymer blends as hole-transporting layers

Q. J. Sun, J. H. Hou, C. H. Yang, Y. F. Li, and Y. Yang

Appl. Phys. Lett. 89, 153501 (2006); http://dx.doi.org/10.1063/1.2360248 (3 pages) | Cited 21 times

Online Publication Date: 9 October 2006

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AU: PLEASE CONFIRM CHANGES MADE IN THE BYLINE.White polymer light-emitting diodes (WPLEDs) with the Commission Internationale de l’Enclairage coordinates of (0.32, 0.34) are demonstrated with poly(9,9-dioctylfluorene-2,7-diyl) as host and poly(5-methoxy-2-(2′-ethyl-hexylthio)-p-phenylenevinylene) as guest. Blends of poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (poly-TPD) and poly(N-vinyl-carbazole) (PVK) are introduced into bilayer devices as hole-transporting layers (HTLs). Because the blends combined the hole-injection and hole-transporting capabilities of poly-TPD with electron-blocking capability of PVK, WPLEDs with the blends as HTLs exhibit enhanced performance in comparison with single-layer device and bilayer devices with pure poly-TPD or pure PVK as HTL. With a 1:1 weight ratio of poly-TPD to PVK in the blend, the WPLED achieves a maximum brightness of ∼ 5000 cd/m2 with a maximum electroluminescent efficiency of 3.15 cd/A.
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85.60.Jb Light-emitting devices

Potential profiling of the nanometer-scale charge-depletion layer in n-ZnO/p-NiO junction using photoemission spectroscopy

Yukiaki Ishida, Atsushi Fujimori, Hiromichi Ohta, Masahiro Hirano, and Hideo Hosono

Appl. Phys. Lett. 89, 153502 (2006); http://dx.doi.org/10.1063/1.2358858 (3 pages) | Cited 9 times

Online Publication Date: 10 October 2006

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The authors have performed a depth-profile analysis of an all-oxide p-n junction diode n-ZnO/p-NiO using photoemission spectroscopy combined with Ar-ion sputtering. Systematic core-level shifts were observed during the gradual removal of the ZnO overlayer, and were interpreted using a model based on charge conservation. Spatial profile of the potential around the interface was deduced, including the charge-depletion width of 2.3 nm extending on the ZnO side and the built-in potential of 0.54 eV.
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79.60.Jv Interfaces; heterostructures; nanostructures
68.37.Ps Atomic force microscopy (AFM)
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.20.At Surface states, band structure, electron density of states
85.30.Kk Junction diodes

Effect of doping profile on the lifetime of green phosphorescent organic light-emitting diodes

Jun Yeob Lee

Appl. Phys. Lett. 89, 153503 (2006); http://dx.doi.org/10.1063/1.2360223 (3 pages) | Cited 21 times

Online Publication Date: 11 October 2006

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The lifetime of green phosphorescent light-emitting diodes was improved by using a graded doping structure in light-emitting layer. A green device with high doping concentration at the hole transport layer and light-emitting layer interface showed longer lifetime than a conventional device with uniform doping concentration for the whole light-emitting layer by more than 60%.
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85.60.Jb Light-emitting devices

Self-consistent simulation of quantum transport and magnetization dynamics in spin-torque based devices

Sayeef Salahuddin and Supriyo Datta

Appl. Phys. Lett. 89, 153504 (2006); http://dx.doi.org/10.1063/1.2359292 (3 pages) | Cited 5 times

Online Publication Date: 11 October 2006

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This letter presents a self-consistent solution of quantum transport, using the nonequilibrium Green’s function method, and magnetization dynamics, using the Landau-Lifshitz-Gilbert formulation. This model is applied to study “spin-torque” induced magnetic switching in a device where the transport is ballistic and the free magnetic layer is sandwiched between two antiparallel (AP) ferromagnetic contacts. A hysteretic current-voltage characteristic is predicted at room temperature, with a sharp transition between the bistable states that can be used as a nonvolatile memory. It is further shown that this AP pentalayer device may allow significant reduction in the switching current, thus facilitating integration of nanomagnets with electronic devices.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Ambipolar organic field-effect transistors fabricated using a composite of semiconducting polymer and soluble fullerene

Shinuk Cho, Jonathan Yuen, Jin Young Kim, Kwanghee Lee, and Alan J. Heeger

Appl. Phys. Lett. 89, 153505 (2006); http://dx.doi.org/10.1063/1.2361269 (3 pages) | Cited 29 times

Online Publication Date: 11 October 2006

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Organic field-effect transistors (FETs) with equivalent hole and electron mobilities have been demonstrated. The devices were fabricated using a phase separated mixture of regioregular poly(3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methyl ester as the active layer and using aluminum (Al) for the source and drain electrodes. Measurements of the source-drain current versus gate voltage gave an electron mobility of μe = 2.0×10−3 cm2/V s and hole mobility of μh = 1.7×10−3cm2/V s. The ambipolar FET properties arise from the use of Al electrodes for the source and drain; the contacts between the Al electrodes and the active layer are improved by thermal annealing at elevated temperatures (150 °C), thereby enabling balanced injection for both holes and electrons in a single device.
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85.30.Tv Field effect devices
61.72.Cc Kinetics of defect formation and annealing
85.65.+h Molecular electronic devices

SiO2/Si3N4/Al2O3 stacks for scaled-down memory devices: Effects of interfaces and thermal annealing

M. Lisiansky, A. Heiman, M. Kovler, A. Fenigstein, Y. Roizin, I. Levin, A. Gladkikh, M. Oksman, R. Edrei, A. Hoffman, Y. Shnieder, and T. Claasen

Appl. Phys. Lett. 89, 153506 (2006); http://dx.doi.org/10.1063/1.2360197 (3 pages) | Cited 15 times

Online Publication Date: 12 October 2006

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Effects of interfaces and thermal annealing on the electrical performance of the SiO2/Si3N4/Al2O3 (ONA) stacks in nonvolatile memory devices were investigated. The results demonstrated the principal role of Si3N4/Al2O3 and Al2O3/metal-gate interfaces in controlling charge retention properties of memory cells. Memory devices that employ both electron and hole trappings were fabricated using a controlled oxidation of nitride surface prior to the Al2O3 growth, a high-temperature annealing of the ONA stack in the N2+O2 atmosphere, and a metal gate electrode having a high work function (Pt). These devices exhibited electrical performance superior to that of their existing SiO2/Si3N4/SiO2 analogs.
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85.30.Tv Field effect devices
84.30.Sk Pulse and digital circuits
61.72.Cc Kinetics of defect formation and annealing
81.65.Mq Oxidation

Effects of C70 derivative in low band gap polymer photovoltaic devices: Spectral complementation and morphology optimization

Yan Yao, Chenjun Shi, Gang Li, Vishal Shrotriya, Qibing Pei, and Yang Yang

Appl. Phys. Lett. 89, 153507 (2006); http://dx.doi.org/10.1063/1.2361082 (3 pages) | Cited 50 times

Online Publication Date: 12 October 2006

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Efficient polymer solar cells based on a low band gap copolymer poly{(9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(3-decyloxythien-2-yl)-2,1,3-benzothiadiazole]-5′,5″-diyl} and (6,6)-phenyl-C71-butyric acid methyl ester (C70-PCBM) were demonstrated with 2.4% power conversion efficiency under air mass 1.5 G, 100 mW/cm2 illumination. The broad absorption peak of C70-PCBM in 440–530 nm complements the absorption valley (regions between two absorption peaks at 416 and 584 nm) of the polymer. The external quantum efficiency measurement further demonstrates that this increased absorption contributes significantly to the generation of photocurrent. Morphology studies on the blend films indicated that excellent miscibility between polymer and C70-PCBM favors exciton separation. The linear relationship between light intensity and short circuit current density shows efficient and balanced charge transport resulting in increased photocurrent and fill factor.
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84.60.Jt Photoelectric conversion
42.70.Jk Polymers and organics
73.61.Ph Polymers; organic compounds
73.61.Wp Fullerenes and related materials
78.66.Tr Fullerenes and related materials
78.66.Qn Polymers; organic compounds

Low-voltage organic transistors on a polymer substrate with an aluminum foil gate fabricated by a laminating and electropolishing process

Chanwoo Yang, Kwonwoo Shin, Sang Yoon Yang, Hayoung Jeon, Danbi Choi, Dae Sung Chung, and Chan Eon Park

Appl. Phys. Lett. 89, 153508 (2006); http://dx.doi.org/10.1063/1.2361265 (3 pages) | Cited 15 times

Online Publication Date: 12 October 2006

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The authors report flexible and low-voltage pentacene organic field-effect transistors (OFETs) constructed with an aluminum foil gate electrode, which was fabricated by the simple and low-cost roll-to-roll lamination process. Electropolishing the surface of laminated aluminum foil and spin coating it with an additional thin polymer film resulted in a gate dielectric surface with a root-mean-square roughness of about 0.85 nm. These pentacene OFETs with a poly(α-methylstyrene)/anodized Al2O3 dual-layered gate dielectric exhibit a mobility of 0.52 cm2/V s, an on-off ratio of 105, a subthreshold swing of 317 mV/decade, and little hysteresis when operating at −5 V.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

High breakdown voltage with low on-state resistance of p-InGaN/n-GaN vertical conducting diodes on n-GaN substrates

Atsushi Nishikawa, Kazuhide Kumakura, and Toshiki Makimoto

Appl. Phys. Lett. 89, 153509 (2006); http://dx.doi.org/10.1063/1.2360227 (3 pages) | Cited 1 time

Online Publication Date: 13 October 2006

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p-InGaN/n-GaN vertical conducting diodes were grown on freestanding n-GaN substrates by metal organic vapor phase epitaxy. The homoepitaxial growth produced a high-quality GaN layer, as evidenced by the full width at half maximum of the (0002) x-ray rocking curve is as low as 34 arc sec. For a diode with a 3.6-μm-thick n-GaN layer, a high breakdown voltage (VB) of 571 V is obtained with a low on-state resistance (Ron) of 1.23 mΩ cm2, leading to the figure of merit, (VB)2/Ron, of 265 MW/cm2. This is the highest value among those previously reported for GaN-based vertical conducting Schottky and p-n junction diodes.
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85.30.Kk Junction diodes
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Effect of InAs dots on noise of quantum dot resonant tunneling single-photon detectors

S. S. Hees, B. E. Kardynal, P. See, A. J. Shields, I. Farrer, and D. A. Ritchie

Appl. Phys. Lett. 89, 153510 (2006); http://dx.doi.org/10.1063/1.2362997 (3 pages) | Cited 11 times

Online Publication Date: 13 October 2006

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The authors present a systematic study of the effect of InAs deposition time on single photon detectors based on quantum dot resonant tunneling diodes. A dramatic improvement in the dark counts due to the electron generation-recombination events in the dots is found by reducing the size of the dots. The dark count rate can be improved to less than 6.6×10−10 ns−1 while maintaining a single photon detection efficiency of 2%.
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85.35.Ds Quantum interference devices
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.60.Gz Photodetectors (including infrared and CCD detectors)
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