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26 Mar 2007

Volume 90, Issue 13, Articles (13xxxx)

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Appl. Phys. Lett. 90, 134101 (2007); http://dx.doi.org/10.1063/1.2679209 (3 pages)

S. Srinivasan, J. Hiller, B. Kabius, and O. Auciello
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Capacitance-voltage characterization of electron beam induced surface cross-linked functional monomers

Santosh Mahapatra, V. N. Bhoraskar, S. A. Gangal, and Dhananjay Bodas

Appl. Phys. Lett. 90, 133501 (2007); http://dx.doi.org/10.1063/1.2716839 (3 pages)

Online Publication Date: 26 March 2007

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A metal-insulator-semiconductor (MIS) capacitor was fabricated using surface cross-linked functional monomers on silicon substrate. Functional monomer: multifunctional acrylates with 3:1 composition were spin coated and later cross-linked under the influence of keV electron irradiation on the surface of silicon to generate a surface-anchored cross-linked network bearing functional moieties. Capacitance-voltage (CV) measurements were carried out before and after electron irradiation. Doping concentration and bulk potential were calculated from the CV curve.
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84.32.Tt Capacitors
85.30.-z Semiconductor devices

Charge carrier generation and electron blocking at interlayers in polymer solar cells

Chunhong Yin, Björn Pieper, Burkhard Stiller, Thomas Kietzke, and Dieter Neher

Appl. Phys. Lett. 90, 133502 (2007); http://dx.doi.org/10.1063/1.2715029 (3 pages) | Cited 18 times

Online Publication Date: 26 March 2007

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The authors show that an electron-donating polymer interlayer and a spin coated layer of an electron-accepting polymer form a defined polymer-polymer heterojunction. Directional photoinduced charge transfer and efficient electron blocking at this heterojunction is clearly seen in Kelvin probe measurements. The photocurrent characteristics of this well-defined bilayer structure as well as of the respective blend device can be consistently fitted by models taking into account only the field dependence of charge carrier generation. Apparently, the efficiency to form free carriers is the determining process in both types of polymer-polymer solar cell structures.
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84.60.Jt Photoelectric conversion

Hysteresis and threshold voltage shift of pentacene thin-film transistors and inverters with Al2O3 gate dielectric

Jae Bon Koo, Chan Hoe Ku, Sang Chul Lim, Seong Hyun Kim, and Jung Hun Lee

Appl. Phys. Lett. 90, 133503 (2007); http://dx.doi.org/10.1063/1.2717015 (3 pages) | Cited 22 times

Online Publication Date: 26 March 2007

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The pentacene organic thin-film transistors (OTFTs) with plasma-enhanced atomic-layer-deposited 150 nm thick Al2O3 as a gate dielectric and the inverters comprised of these OTFTs have been fabricated. The hysteresis in transfer characteristics of the OTFTs depends on the scan range of negative gate voltage, regardless of drain voltage. Negative gate-bias stress leads to the progressive negative shift of threshold voltage. The hysteresis of D inverter is similar to that of E inverter, but the former has a wider swing range and a higher gain in comparison with the latter.
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85.30.Tv Field effect devices

Optimum charge carrier mobility in organic solar cells

M. M. Mandoc, L. J. A. Koster, and P. W. M. Blom

Appl. Phys. Lett. 90, 133504 (2007); http://dx.doi.org/10.1063/1.2711534 (3 pages) | Cited 60 times

Online Publication Date: 27 March 2007

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In organic semiconductors the recombination mechanism is of the Langevin type, controlled by the mobility of the charge carriers. As a result, in organic solar cells the mobility simultaneously controls both the carrier extraction and the losses via carrier recombination. The authors demonstrate that the balance between carrier losses by extraction and by recombination leads to a distinct optimum in the carrier mobility with regard to the efficiency of organic solar cells. For low mobilities recombination losses limit the performance, whereas the efficient extraction at high mobilities leads to a reduction of the open-circuit voltage.
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84.60.Jt Photoelectric conversion

Magnetic-fluid optical-fiber modulators via magnetic modulation

J. J. Chieh, S. Y. Yang, H. E. Horng, Chin-Yih Hong, and H. C. Yang

Appl. Phys. Lett. 90, 133505 (2007); http://dx.doi.org/10.1063/1.2716365 (3 pages) | Cited 21 times

Online Publication Date: 28 March 2007

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The authors develop an optical-fiber modulator using magnetic fluid as a cladding layer in this work. By applying magnetic fields, the authors reduced the optical-fiber modulator transmission. Experimental results show that the magnetically induced transmission loss of an optical-fiber modulator under external magnetic fields is dominated by the number of magnetic clusters in the cladding magnetic fluid. Furthermore, it was observed that the formation of magnetic clusters depends on the length of the fiber modulator. In this work, the authors also develop a theoretical model to clarify the transmission characterization of magnetic-fluid optical-fiber modulators.
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42.81.Wg Other fiber-optical devices
85.70.Sq Magnetooptical devices
42.79.Hp Optical processors, correlators, and modulators
75.50.Mm Magnetic liquids

Fermi energy pinning at the surface of high mobility In0.53Ga0.47As/In0.52Al0.48As modulation doped field effect transistor structures

E. Skuras and C. R. Stanley

Appl. Phys. Lett. 90, 133506 (2007); http://dx.doi.org/10.1063/1.2716844 (3 pages)

Online Publication Date: 28 March 2007

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Fermi level pinning at the surface of the undoped In0.52Al0.48As Schottky layer in high mobility In0.53Ga0.47As/In0.52Al0.48As modulation doped field effect transistor structures has been studied. The electron subband densities for samples prepared with different Schottky layer thicknesses have been deduced from fast Fourier transform analyses of 1.5 K Shubnikov-de Haas data. These results have been compared with densities calculated self-consistently using the free surface potential ΦS as the only fitting parameter. Good agreement between theory and experiment is achieved for a surface Fermi energy pinned 0.65±0.05 eV below the In0.52Al0.48As Γ-conduction band minimum.
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85.30.Tv Field effect devices

Electronic switching device based on gate-controlled conductivity anisotropy

O. Bierwagen and W. T. Masselink

Appl. Phys. Lett. 90, 133507 (2007); http://dx.doi.org/10.1063/1.2717523 (3 pages) | Cited 1 time

Online Publication Date: 28 March 2007

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A five-terminal electronic switching device based on gate-controlled transport anisotropy is proposed. By means of the gate voltage, two output voltages can be contrariwise adjusted to values between the two input voltages, yielding a possible logic application as an exchange gate. Nanostructures, in the form of modulation-doped, self-organized InAs quantum wires embedded in InP are investigated and shown to be a candidate for implementation of this device.
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85.30.Tv Field effect devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

High-efficiency low operation voltage organic light-emitting diodes

Chong-an Di, Gui Yu, Yunqi Liu, Xinjun Xu, Yabin Song, and Daoben Zhu

Appl. Phys. Lett. 90, 133508 (2007); http://dx.doi.org/10.1063/1.2718274 (3 pages) | Cited 15 times

Online Publication Date: 28 March 2007

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The authors report a simple approach to reduce power consumption of organic light-emitting diodes. Introducing a 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline layer into the emissive layer can dramatically improve the carrier recombination efficiency. The presence of an interlayer of tris(8-quinolinolato)aluminum (Alq3) within the hole-transport layer also gives rise to the similar phenomenon. Furthermore, they modified the anode with the ultrathin hexadecafluorocopper phthalocyanine layer in order to further enhance the electroluminescent properties. They obtained the high performance light-emitting diodes using Alq3 as the emissive layer with a high current efficiency of 7.63 cd/A and a low turn-on voltage of 2.89 V.
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85.60.Jb Light-emitting devices

Enhanced photovoltaic response of organic solar cell by singlet-to-triplet exciton conversion

Chia-Ming Yang, Chi-Hui Wu, Hua-Hsin Liao, Kuei-Yuan Lai, Hong-Ping Cheng, Sheng-Fu Horng, Hsin-Fei Meng, and Jow-Tsong Shy

Appl. Phys. Lett. 90, 133509 (2007); http://dx.doi.org/10.1063/1.2716209 (3 pages) | Cited 10 times

Online Publication Date: 29 March 2007

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Ir complex was doped to conjugated polymers, and the photoinduced absorption of triplet excitons in host materials was examined. A greatly enhanced intersystem crossing rate was observed, despite the decrease in triplet exciton lifetime. The authors find that the steady-state triplet exciton population in host polymer would increase by an order of magnitude. Conjugated polymer/colloidal CdSe nanocrystal hybrid solar cells were fabricated and the effect of Ir-complex doping on photovoltaic response was studied. It was found that due to the enhanced singlet-to-triplet conversion, greatly enhanced photovoltaic response of these hybrid organic solar cells was observed. The results suggest that triplet solar cells may be achieved by doping conventional photovoltaic materials with transition-metal complexes.
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84.60.Jt Photoelectric conversion

Isotopic labeling study of the oxygen diffusion in HfO2/SiO2/Si

Ming Zhao, Kaoru Nakajima, Motofumi Suzuki, Kenji Kimura, Masashi Uematsu, Kazuyoshi Torii, Satoshi Kamiyama, Yasuo Nara, Heiji Watanabe, Kenji Shiraishi, Toyohiro Chikyow, and Keisaku Yamada

Appl. Phys. Lett. 90, 133510 (2007); http://dx.doi.org/10.1063/1.2717539 (3 pages) | Cited 6 times

Online Publication Date: 29 March 2007

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The characteristic oxygen diffusion in HfO2/SiO2/Si structure during the annealing in oxygen has been investigated by high-resolution Rutherford backscattering spectroscopy in combination with oxygen isotope substitution at 900 °C in 0.1 Torr 18O2. The observed 18O profile suggests that oxygen molecules are decomposed into atomic oxygen in the HfO2 layer and diffuse through the oxide layer via exchange mechanism. This is also supported by the observed activation energy of ∼ 0.6 eV for the growth of the interfacial SiO2 layer.
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66.30.Ny Chemical interdiffusion; diffusion barriers
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
81.40.Gh Other heat and thermomechanical treatments

Air stable, high performance pentacene thin-film transistor fabricated on SiO2 gate insulator treated with β-phenethyltrichlorosilane

Daisuke Kumaki, Masayuki Yahiro, Youji Inoue, and Shizuo Tokito

Appl. Phys. Lett. 90, 133511 (2007); http://dx.doi.org/10.1063/1.2717552 (3 pages) | Cited 34 times

Online Publication Date: 29 March 2007

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A pentacene thin-film transistor (TFT) was fabricated on a SiO2 gate insulator treated with β-phenethyltrichlorosilane (β-PTS). Employing β-PTS for the surface treatment of SiO2, large grains were present in the initial stage of pentacene crystal growth. The field effect mobility was as high as 1.5 cm2/V s and the on/off ratio was over 106. The surface treatment dramatically improved the stability in air of the pentacene-TFT’s electrical characteristics. A field effect mobility of over 1 cm2/V s and on/off ratio of over 105 were maintained after scanning the gate voltage 2000 times in air. This result indicates that the surface treatment with β-PTS not only improved TFT performance but also significantly suppressed the device’s degradation.
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85.30.Tv Field effect devices

Noise characteristics of 100 nm scale GaAs/AlxGa1−xAs scanning Hall probes

C. W. Hicks, L. Luan, K. A. Moler, E. Zeldov, and H. Shtrikman

Appl. Phys. Lett. 90, 133512 (2007); http://dx.doi.org/10.1063/1.2717565 (3 pages) | Cited 7 times

Online Publication Date: 29 March 2007

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The authors have fabricated and characterized GaAs/AlxGa1−xAs two-dimensional electron gas scanning Hall probes for imaging perpendicular magnetic fields at surfaces. The Hall crosses range from 85×85 to 1000×1000 nm2. They study low-frequency noise in these probes, especially random telegraph noise, and show that low-frequency noise can be significantly reduced by optimizing the voltage on a gate over the Hall cross. The authors demonstrate a 100 nm Hall probe with a sensitivity of 0.5 G/√Hz (flux sensitivity of 0.25mΦ0/√Hz; spin sensitivity of 1.2×104μB/√Hz) at 3 Hz and 9 K.
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73.63.-b Electronic transport in nanoscale materials and structures
72.70.+m Noise processes and phenomena
72.20.My Galvanomagnetic and other magnetotransport effects
07.55.Ge Magnetometers for magnetic field measurements

Control of reverse twist domain near a pixel edge using strong vertical electric field in the fringe-field switching liquid crystal device

Mi Sook Kim, Seung Min Seen, and Seung Hee Lee

Appl. Phys. Lett. 90, 133513 (2007); http://dx.doi.org/10.1063/1.2715494 (3 pages) | Cited 5 times

Online Publication Date: 29 March 2007

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In the fringe-field switching (FFS) liquid crystal (LC) device, competition between two opposite forces to twist LCs exists near the pixel edge. The authors proposed an advanced FFS structure with the strong vertical field near the pixel edge which was induced between Cr black matrix (BM) and pixel electrode due to electrical connection between the Cr BM and the common electrode. The vertical field induces a tilt angle of LCs which increases with increasing field intensity. As a result, the degree of twist in the reverse direction decreases with increasing the pixel voltage, and thus voltage-dependent LC dynamics becomes very stable even at high applied voltages.
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42.79.Kr Display devices, liquid-crystal devices

Organic thin-film transistor integration using silicon nitride gate dielectric

Flora M. Li, Arokia Nathan, Yiliang Wu, and Beng S. Ong

Appl. Phys. Lett. 90, 133514 (2007); http://dx.doi.org/10.1063/1.2718505 (3 pages) | Cited 15 times

Online Publication Date: 30 March 2007

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The impact of film composition of silicon nitride (SiNx) gate dielectrics on the electrical performance of organic thin-film transistors (OTFTs) was investigated. Polythiophene OTFTs with SiNx dielectric, prepared using a series of interface modification processes, exhibited effective mobility of 0.09 cm2/V s and on/off current ratio of 107. Overall improvement in mobility, on/off current ratio, and gate leakage current was observed as silicon content in SiNx increases. The results demonstrate the viability of using SiNx for OTFTs. The low temperature processing and large area deposition capabilities of SiNx hold great promise for integration of OTFT circuits for large area flexible electronic applications.
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85.30.Tv Field effect devices

Optical geometries for fiber-based organic photovoltaics

Jiwen Liu, Manoj A. G. Namboothiry, and David L. Carroll

Appl. Phys. Lett. 90, 133515 (2007); http://dx.doi.org/10.1063/1.2716864 (3 pages) | Cited 15 times

Online Publication Date: 30 March 2007

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Poly(3-hexylthiophene):1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 photovoltaic devices were fabricated as a cladding onto large diameter optical fibers. The performance of the devices was dependent on fiber diameter as well as the angle of incidence of light onto the cleaved fiber face. The authors suggest that absorption by the active layer is dominated by different mechanisms at different angles: evanescent coupling of the light at small incident angles and far field scattering of the light from the fiber at higher angles. Further, a comparison of devices that only partially clad the fiber to those that fully clad suggests the formation of confined radiation modes.
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42.81.Bm Fabrication, cladding, and splicing
42.15.-i Geometrical optics
72.40.+w Photoconduction and photovoltaic effects

Temperature dependence of Hall effects in organic thin-film transistors on plastic films

Yasushi Takamatsu, Tsuyoshi Sekitani, and Takao Someya

Appl. Phys. Lett. 90, 133516 (2007); http://dx.doi.org/10.1063/1.2717144 (3 pages) | Cited 5 times

Online Publication Date: 30 March 2007

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The authors investigated the temperature dependence of Hall effects on polycrystalline pentacene thin-film transistors manufactured on plastic base films. The temperature dependence of the charge amounts evaluated from the Hall effect measurements is systematically compared with that evaluated from capacitance-voltage (CV) measurements. Our result indicates that the conduction carriers are dominated by hopping between polycrystalline grain boundaries below 260 K and tend to be delocalized above 260 K.
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85.30.Tv Field effect devices
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