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26 Nov 2007

Volume 91, Issue 22, Articles (22xxxx)

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Appl. Phys. Lett. 91, 222101 (2007); http://dx.doi.org/10.1063/1.2815931 (3 pages)

H. T. Wang, B. S. Kang, F. Ren, S. J. Pearton, J. W. Johnson, P. Rajagopal, J. C. Roberts, E. L. Piner, and K. J. Linthicum
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Air stable hybrid organic-inorganic light emitting diodes using ZnO as the cathode

Henk J. Bolink, Eugenio Coronado, Diego Repetto, and Michele Sessolo

Appl. Phys. Lett. 91, 223501 (2007); http://dx.doi.org/10.1063/1.2809387 (3 pages) | Cited 42 times

Online Publication Date: 26 November 2007

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An air stable hybrid organic-inorganic light emitting device is presented. This architecture makes use of metal oxides as charge injecting materials into the light emitting polymer, avoiding the use of air sensitive cathodes commonly employed in organic light emitting diode manufacturing. We report the application of zinc oxide as a cathode in an organic light emitting device. This electroluminescent device shows high brightness levels reaching 6500 cd/m2 at voltages as low as 8 V. Compared to a conventional device using low workfunction metal cathodes, our device shows a lower turn-on voltage and it can operate in air.
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81.07.Pr Organic-inorganic hybrid nanostructures
85.60.Jb Light-emitting devices
82.45.Fk Electrodes

Ga2O3(Gd2O3)/Si3N4 dual-layer gate dielectric for InGaAs enhancement mode metal-oxide-semiconductor field-effect transistor with channel inversion

J. F. Zheng, W. Tsai, T. D. Lin, Y. J. Lee, C. P. Chen, M. Hong, J. Kwo, S. Cui, and T. P. Ma

Appl. Phys. Lett. 91, 223502 (2007); http://dx.doi.org/10.1063/1.2817742 (3 pages) | Cited 16 times

Online Publication Date: 26 November 2007

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A dual-layer gate dielectric approach for application in III-V metal-oxide-semiconductor field-effect transistor (MOSFET) was studied by using ultrahigh vacuum deposited 7–8 nm thick Ga2O3(Gd2O3) as the initial dielectric to unpin the surface Fermi level of In0.18Ga0.82As and then molecular-atomic deposition of ∼ 2–3 nm thick Si3N4 as a second dielectric protecting Ga2O3(Gd2O3). The total equivalent oxide thickness achieved in this study is 5 nm. We have demonstrated an enhancement mode In0.18Ga0.82As/GaAs MOSFET with surface inverted n channel with drain current (Id) of 0.1 mA for a gate length of 10 μm and a gate width of 880 μm at Vds = 1 V and Vg = 4.5 V.
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85.30.Tv Field effect devices
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Optofluidic tuning of photonic crystal band edge lasers

Felipe Bernal Arango, Mads Brøkner Christiansen, Morten Gersborg-Hansen, and Anders Kristensen

Appl. Phys. Lett. 91, 223503 (2007); http://dx.doi.org/10.1063/1.2817610 (3 pages) | Cited 17 times

Online Publication Date: 26 November 2007

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We demonstrate optofluidic tuning of polymer photonic crystal band edge lasers with an imposed rectangular symmetry. The emission wavelength depends on both lattice constant and cladding refractive index. The emission wavelength is shown to change 1 nm with a cladding refractive index change of 10−2. The rectangular symmetry modification alters the emission characteristics of the devices and the relative emission intensities along the symmetry axes depend on cladding refractive index, suggesting a sensor concept based on detection of intensity rather than wavelength.
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42.55.Tv Photonic crystal lasers and coherent effects
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking
42.82.-m Integrated optics
47.85.Np Fluidics
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Resistive switching properties of high crystallinity and low-resistance Pr0.7Ca0.3MnO3 thin film with point-contacted Ag electrodes

Masayuki Fujimoto, Hiroshi Koyama, Yuji Nishi, and Toshimasa Suzuki

Appl. Phys. Lett. 91, 223504 (2007); http://dx.doi.org/10.1063/1.2816124 (3 pages) | Cited 23 times

Online Publication Date: 26 November 2007

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A high-crystallinity, low-resistance Pr0.7Ca0.3MnO3(PCMO) thin film deposited by sputtering at 600 °C showed no resistive switching with a Pt/Pr0.7Ca0.3MnO3/Pt structure but a remarkable bipolar resistive switching with a Ag paste/Pr0.7Ca0.3MnO3/Pt structure. Observed retention fatigue of the low-resistance state was almost saturated after 24 h. The resistive switching properties were characterized as point contact of Ag grains to PCMO thin film. It was also found that the interface can form interfacial trap states and resistive change active layers. This strongly suggests that the function of the Ag point contact is similar to those of the previously proposed filament path and the nanodomain switch.
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73.40.Sx Metal-semiconductor-metal structures
81.15.Cd Deposition by sputtering
73.61.Le Other inorganic semiconductors
73.20.-r Electron states at surfaces and interfaces
68.35.Gy Mechanical properties; surface strains

rf-microwave switches based on reversible semiconductor-metal transition of VO2 thin films synthesized by pulsed-laser deposition

F. Dumas-Bouchiat, C. Champeaux, A. Catherinot, A. Crunteanu, and P. Blondy

Appl. Phys. Lett. 91, 223505 (2007); http://dx.doi.org/10.1063/1.2815927 (3 pages) | Cited 8 times

Online Publication Date: 27 November 2007

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Microwave switching devices based on the semiconductor-metal transition of VO2 thin films were developped on two types of substrates (C-plane sapphire and SiO2/Si), and in both shunt and series configurations. Under thermal activation, the switches achieved up to 30–40 dB average isolation of the radio-frequency (rf) signal on 500 MHz–35 GHz frequency band with weak insertion losses. These VO2-based switches can be electrically activated with commutation times less than 100 ns, which make them promising candidates for realizing efficient and simple rf switches.
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84.32.Dd Connectors, relays, and switches
81.15.Fg Pulsed laser ablation deposition
71.30.+h Metal-insulator transitions and other electronic transitions

Multistable liquid crystal waveplate

G. G. Wells and C. V. Brown

Appl. Phys. Lett. 91, 223506 (2007); http://dx.doi.org/10.1063/1.2816400 (3 pages) | Cited 3 times

Online Publication Date: 27 November 2007

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A multistable liquid crystal waveplate has been produced by confining a roughly disk-shaped nematic liquid crystal droplet of diameter 50 μm between two photoresist coated surfaces separated by 15 μm. Dimple features occur on opposite sides of the curve-free edge of the droplet, which may indicate the position of nematic disclinations. The diameter that connects these features coincides with an optic axis of the droplet. In-plane ac voltage bursts produce an optic axis rotation, controllable down to 1° steps, to other arbitrary, stable orientations. The rotation angle is proportional to the burst duration and the voltage squared.
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42.70.Df Liquid crystals
42.25.Ja Polarization
42.82.Cr Fabrication techniques; lithography, pattern transfer

Thermodynamic limits of quantum photovoltaic cell efficiency

Guodan Wei, Kuen-Ting Shiu, Noel C. Giebink, and Stephen R. Forrest

Appl. Phys. Lett. 91, 223507 (2007); http://dx.doi.org/10.1063/1.2817753 (3 pages) | Cited 19 times

Online Publication Date: 27 November 2007

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The intermediate band solar cell has been proposed as an ultrahigh efficiency source of energy due to the possibility of absorption of two sequential sub-band-gap photons to excite charge from a quantum confined (e.g., quantum dot or well) region into the large band gap barrier region [ A. Luque and A. Martí, Phys. Rev. Lett. 78, 5014 (1997) ]. Unfortunately, high efficiencies using this structure have not yet been realized. Here, we analyze the fundamental limits to power generation in quantum solar cells. When a difference in quasi-Fermi energies between the barrier and the quantum well regions exists due to the presence of photogenerated charge, an upper efficiency limit of 44.5% is achievable due to single photon absorption only. This efficiency is significantly higher than the Shockley-Queisser limit of ∼ 31% for homojunction cells, but remains below that predicted for two photon excitation (>63%) previously predicted for quantum cells.
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72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects
84.60.Jt Photoelectric conversion

Enhancement in open circuit voltage through a cascade-type energy band structure

Srinivas Sista, Yan Yao, Yang Yang, Ming Lee Tang, and Zhenan Bao

Appl. Phys. Lett. 91, 223508 (2007); http://dx.doi.org/10.1063/1.2817935 (3 pages) | Cited 27 times

Online Publication Date: 27 November 2007

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In this paper, we report a method to increase the open-circuit voltage (VOC) of an organic solar cell by inserting an interfacial layer between the donor and acceptor layers to form a cascade-type energy band structure. We demonstrate its feasibility using a recently reported asymmetric pentacene derivative, tetraceno[2,3-b]thiophene (TT) as a donor material, C60 as an acceptor material, and copper phthalocyanine (CuPc) as the sandwich layer. The VOC was increased from 0.3 V for the device with no CuPc sandwich layer to 0.56 V for 13 nm thick CuPc layer. The power conversion efficiency (PCE) of the device with 13 nm CuPc layer was 1.53% and the fill factor (FF) was 0.64, in comparison to TT/C60 device which had a PCE of 0.78% and a FF of 0.52.
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84.60.Jt Photoelectric conversion

Effects of interfacial stability between electron transporting layer and cathode on the degradation process of organic light-emitting diodes

Ta-Ya Chu, Yong-Han Lee, and Ok-Keun Song

Appl. Phys. Lett. 91, 223509 (2007); http://dx.doi.org/10.1063/1.2817939 (3 pages) | Cited 10 times

Online Publication Date: 27 November 2007

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The authors have demonstrated that the increase of electron injection barrier height between tris(8-hydroxyquinoline)aluminum (Alq3) and LiF/Al cathode is one of the most critical parameters to determine the reliability of organic light-emitting diode with the typical structure of indium tin oxide/N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl) benzidine/Alq3/LiF/Al. The electrical properties of several devices (hole only, electron only, and integrated double-layered devices) have been measured in the function of operating time to analyze the bulk and interface property changes. Bulk properties of trap energy and mobility in an organic layer have been estimated by using trap-charge-limited currents and transient electroluminescence measurements.
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85.60.Jb Light-emitting devices
73.40.Ns Metal-nonmetal contacts
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

High speed resistive switching in Pt/TiO2/TiN film for nonvolatile memory application

Chikako Yoshida, Kohji Tsunoda, Hideyuki Noshiro, and Yoshihiro Sugiyama

Appl. Phys. Lett. 91, 223510 (2007); http://dx.doi.org/10.1063/1.2818691 (3 pages) | Cited 65 times

Online Publication Date: 29 November 2007

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We have fabricated and investigated the bipolar resistive switching characteristics of Pt/rutile-TiO2/TiN devices for resistance memory applications. Data writing for five-level resistance states has been demonstrated by varying the amplitude of 5 ns voltage pulses. In addition, data retention of more than 256 h at 85 °C and an excellent endurance of over 2×106 cycles have been confirmed. These results indicate that Pt/TiO2/TiN devices have a potential for nonvolatile multiple-valued memory devices.
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84.30.Sk Pulse and digital circuits
73.40.Ns Metal-nonmetal contacts

Optical capacitance-voltage characterization of charge traps in the trapping nitride layer of charge trapped flash memory devices

Jang Uk. Lee, Kang Seob Roh, Gu Cheol Kang, Seung Hwan Seo, Kwan Young Kim, Sunyeong Lee, Kwan Jae Song, Chang Min Choi, So Ra Park, Jun Hyun Park, Ki Chan Jeon, Dae Hwan Kim, Byung-Gook Park, Jong Duk Lee, and Dong Myong Kim

Appl. Phys. Lett. 91, 223511 (2007); http://dx.doi.org/10.1063/1.2819092 (3 pages) | Cited 4 times

Online Publication Date: 29 November 2007

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Extracting the trap distribution in charge trapping layers of charge trap flash memory devices, an optical C-V method (OCVM) is proposed. Applying photons with λ = 532 nm to the oxide-nitride-oxide layer with 50/60/23 Å in metal-oxide-nitride-oxide-semiconductor charge trap flash devices, the trap density in the charge trapping nitride layer is extracted to be 1.16×1018–1.67×1019 cm−3 eV−1 over the energy EC−Et = 1.36–1.64 eV. Combining sub-band-gap photons in C-V characterization, the OCVM method is free from the thermal and electrical stresses which are inherent in conventional characterization methods even though they are critical error factors for accurate characterization of charge trapped flash memory devices.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Poly(3,3‴-didodecylquarterthiophene) field effect transistors with single-walled carbon nanotube based source and drain electrodes

Yuan Yuan Zhang, Yumeng Shi, Fuming Chen, S. G. Mhaisalkar, Lain-Jong Li, Beng S. Ong, and Yiliang Wu

Appl. Phys. Lett. 91, 223512 (2007); http://dx.doi.org/10.1063/1.2806234 (3 pages) | Cited 11 times

Online Publication Date: 30 November 2007

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A solution processable method for employing single-walled carbon nanotubes (SWCNTs) as bottom contact source/drain electrodes for a significant reduction of contact resistance in poly(3,3‴-didodecylquarterthiophene) based organic field effect transistors (OFETs) is proposed. A two order of magnitude reduction in contact resistance and up to a threefold improvement in field effect mobilities were observed in SWCNT contacted OFETs as opposed to similar devices with gold source/drain electrodes. Based on Kelvin probe measurements, this improvement was attributed to a reduction in the Schottky barrier for hole injection into organic semiconductor.
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85.30.Tv Field effect devices
85.35.Kt Nanotube devices
73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Cg Contact resistance, contact potential

Mechanism for generation of the phonon-energy-coupling enhancement effect for ultrathin oxides on silicon

Zhi Chen

Appl. Phys. Lett. 91, 223513 (2007); http://dx.doi.org/10.1063/1.2820383 (3 pages) | Cited 4 times

Online Publication Date: 30 November 2007

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Large leakage-current reduction of SiO2 due to the phonon-energy-coupling enhancement effect was confirmed by measuring the oxide thickness using a cross-sectional transmission electron microscopy. There is a critical temperature Tc. Rapid thermal processing (RTP) of SiO2 at T>Tc in pure N2 leads to a destructive structure with large leakage current, while RTP at T<Tc in pure N2 does not change the oxide structure. After introducing a little amount of oxygen during RTP, the destructive structure can be converted to a constructive one by repairing the defects created during RTP at T>Tc. This leads to reduced leakage current.
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81.65.-b Surface treatments
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