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15 Jan 2007

Volume 90, Issue 3, Articles (03xxxx)

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Appl. Phys. Lett. 90, 032108 (2007); http://dx.doi.org/10.1063/1.2431702 (3 pages)

D. Buca, B. Holländer, S. Feste, St. Lenk, H. Trinkaus, S. Mantl, R. Loo, and M. Caymax
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Investigation of drain current transient in BCB- and SiN-passivated Al0.25Ga0.75As/In0.2Ga0.8As pseudomorphic high electron mobility transistors

Chee Leong Tan, Hong Wang, and K. Radhakrishnan

Appl. Phys. Lett. 90, 033501 (2007); http://dx.doi.org/10.1063/1.2431766 (3 pages) | Cited 2 times

Online Publication Date: 16 January 2007

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The authors report on the drain current transient of Al0.25Ga0.75As/In0.2Ga0.8As pseudomorphic high electron mobility transistors passivated by low-k benzocyclobutene (BCB). Compared to the more commonly used silicon nitride, BCB has a lower dielectric constant and loss tangent and is becoming popular for passivation. However, its effect on the device drain current transient has not been studied so far. In this work, the effectiveness of BCB as a passivation material was investigated in relation to the device drain current transient response. The surface trap model was also used to describe the transient behavior quantitatively.
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85.30.Tv Field effect devices

High performance organic thin-film transistors with photopatterned gate dielectric

Sun Hee Lee, Dong Joon Choo, Seung Hoon Han, Jun Hee Kim, Young Rea Son, and Jin Jang

Appl. Phys. Lett. 90, 033502 (2007); http://dx.doi.org/10.1063/1.2425012 (3 pages) | Cited 18 times

Online Publication Date: 16 January 2007

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The authors have fabricated high performance pentacene organic thin-film transistor (OTFT) using photopatternable poly(4-vinylphenol) gate dielectric on plastic substrate. The dielectric layer was composed of poly(vinylphenol), 1,2,4,5-tetraacetoxymethylbenzene, and 2,4-bis(trichloro methyl)-6-aryl-1,3,5-triazine. The 1,2,4,5-tetraacetoxymethylbenzene is a cross-linking material which is synthesized by a two-step reaction. The gate dielectric was patterned by spin coating and UV exposure. The OTFT with photopatterned gate dielectric exhibited a field-effect mobility of 1.23 cm2/V s and a threshold voltage of −6.5 V and an on/off current ratio of 107, so that the OTFT can be applied to make a high performance display.
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85.30.Tv Field effect devices
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Consideration of switching mechanism of binary metal oxide resistive junctions using a thermal reaction model

Yoshihiro Sato, Kentaro Kinoshita, Masaki Aoki, and Yoshihiro Sugiyama

Appl. Phys. Lett. 90, 033503 (2007); http://dx.doi.org/10.1063/1.2431792 (3 pages) | Cited 42 times

Online Publication Date: 16 January 2007

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The authors investigated the resistive switching of transition metal oxide (TMO) junctions by applying a short voltage pulse and found that the response time of the “reset” process was dependent on the resistance in the low resistive state. By using a thermal conductive equation to calculate the temperature of the filamentary conductive path in the TMO film, the temperature in the reset process was estimated to reach the same temperature grade in each reset. On this basis, the previous experimental relation is well explained by assuming a general thermal chemical reaction model for the reset process.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
82.60.-s Chemical thermodynamics
73.40.Rw Metal-insulator-metal structures

Trap elimination and injection switching at organic field effect transistor by inserting an alkane (C44H90) layer

Satoshi Ogawa, Yasuo Kimura, Michio Niwano, and Hisao Ishii

Appl. Phys. Lett. 90, 033504 (2007); http://dx.doi.org/10.1063/1.2431713 (3 pages) | Cited 16 times

Online Publication Date: 17 January 2007

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Recently, it was proposed in the literature that the electron trap on a hydroxyl-containing dielectric interface of an organic field effect transistor (OFET) hinders its n type operation. The authors fabricated pentacene and fullerene OFETs with a hydroxyl-free insulating material, a long-chain alkane, i.e., tetratetracontate (TTC), C44H90 layer coated on the SiO2 dielectric layer. The displacement current measurements clearly demonstrated that the electron trap of the SiO2 surface is suppressed by the TTC layer. For a pentacene FET with an Al electrode and SiO2 dielectric layer, a p type operation was observed, while the operation mode was switched to the n type by the insertion of TTC on the SiO2 interface. By simple patterning of the TTC layer to produce a bipolar injection, the authors fabricated an ambipolar pentacene FET with a single kind of metal electrode. Thus TTC is a good material for the surface modification of a dielectric layer in OFETs.
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85.30.Tv Field effect devices
85.30.Pq Bipolar transistors
85.65.+h Molecular electronic devices

Multiplexed hydraulic valve actuation using ionic liquid filled soft channels and Braille displays

Wei Gu, Hao Chen, Yi-Chung Tung, Jens-Christian Meiners, and Shuichi Takayama

Appl. Phys. Lett. 90, 033505 (2007); http://dx.doi.org/10.1063/1.2431771 (3 pages) | Cited 11 times

Online Publication Date: 17 January 2007

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Pneumatic actuation with multilayer soft lithography enables operation of up to thousands of valves in parallel using far fewer control lines. However, it is dependent on macroscopic switches and external pressure sources that require interconnects and limit portability. The authors present a more portable and multiplexed valve actuation strategy that uses a grid of mechanically actuated Braille pins to hydraulically, rather than pneumatically, deform elastic actuation channels that act as valves. Experimental and theoretical analyses show that the key to reliable operation of the hydraulic system is the use of nonvolatile ionic liquids as the hydraulic fluid.
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87.80.-y Biophysical techniques (research methods)
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
47.85.Kn Hydraulic and pneumatic machinery
47.60.-i Flow phenomena in quasi-one-dimensional systems
47.85.Np Fluidics
07.10.Cm Micromechanical devices and systems

Spectral broadening in electroluminescence of white organic light-emitting diodes based on complementary colors

Young Min Kim, Young Wook Park, Jin Hwan Choi, Byeong Kwon Ju, Jae Hoon Jung, and Jai Kyeong Kim

Appl. Phys. Lett. 90, 033506 (2007); http://dx.doi.org/10.1063/1.2431773 (3 pages) | Cited 13 times

Online Publication Date: 17 January 2007

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The authors report the optical and electroluminescent (EL) properties of white organic light-emitting diodes (OLEDs) which have two emitters with similar structures: 1, 1, 4, 4-tetraphenyl-1, 3-butadiene and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline have an emission peak of 400 nm around the near ultraviolet, and tris-(8-hydroxyquinoline) aluminum doped with 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran has an emission peak of 580 nm producing a yellow color. The EL spectra of the white OLED have shown a broadening through visual range from 400 to 780 nm. This spectral broadening is related to an exciplex emission at the organic solid interface.
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85.60.Jb Light-emitting devices

Charge offset stability in tunable-barrier Si single-electron tunneling devices

Neil M. Zimmerman, Brian J. Simonds, Akira Fujiwara, Yukinori Ono, Yasuo Takahashi, and Hiroshi Inokawa

Appl. Phys. Lett. 90, 033507 (2007); http://dx.doi.org/10.1063/1.2431778 (3 pages) | Cited 14 times

Online Publication Date: 17 January 2007

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The problem of charge offset drift in single-electron tunneling (SET) devices can preclude their useful application in metrology and integrated devices. We demonstrate that in tunable-barrier Si-based SET transistors there is excellent stability, with a drift that is in general less than 0.01e; these devices exhibit some unwanted sensitivity to external perturbations including temperature excursions. Finally, we show that these devices can be “trained” to minimize their sensitivity to abrupt voltage changes.
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85.35.Gv Single electron devices

Complete ground state gain recovery after ultrashort double pulses in quantum dot based semiconductor optical amplifier

Sabine Dommers, Vasily V. Temnov, Ulrike Woggon, Jordi Gomis, Juan Martinez-Pastor, Matthias Laemmlin, and Dieter Bimberg

Appl. Phys. Lett. 90, 033508 (2007); http://dx.doi.org/10.1063/1.2431789 (3 pages) | Cited 33 times

Online Publication Date: 17 January 2007

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Gain recovery dynamics are studied in electrically pumped quantum dot (QD) based semiconductor optical amplifiers (SOAs) after amplification of double femtosecond laser pulses using ultrafast pump-probe spectroscopy with heterodyne detection. The authors observe a distinct change in gain recovery in the ground state when a significant excited state population is achieved. A complete gain recovery is found when two 150 fs pulses with 5 ps time delay pass through the SOA in resonance to the ground state under high injection currents of 80–100 mA. The obtained results open the way for ultrafast (>200 GHz) operation in p-doped QD based SOAs at 1.3 μm telecommunications wavelengths.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Control of the defect in the liquid crystal director field on the slit of the patterned vertical alignment cell

Gi-Dong Lee, Jung-Hee Son, Yong-Hyun Choi, Jae-Jin Lju, Kyeong Hyeon Kim, and Seung Hee Lee

Appl. Phys. Lett. 90, 033509 (2007); http://dx.doi.org/10.1063/1.2432251 (3 pages) | Cited 10 times

Online Publication Date: 17 January 2007

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In this letter the authors studied the method to control the position of the generated defect on the slit of the patterned vertical alignment liquid crystal (LC) cell with dynamic stability. The authors modeled the LC director field with a defect on the slit and proposed an advanced wing pattern with a defect trap to stick the defect outside the active area. This shape can prevent the generation of the defect on the slit in the active area even if the authors increase the operation voltage, so that the LC dynamics on the slit is very stable and optical transmittance becomes higher.
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42.70.Df Liquid crystals
61.30.-v Liquid crystals

Faster electro-optical response characteristics of a carbon-nanotube-nematic suspension

Hui-Yu Chen, Wei Lee, and Noel A. Clark

Appl. Phys. Lett. 90, 033510 (2007); http://dx.doi.org/10.1063/1.2432294 (3 pages) | Cited 32 times

Online Publication Date: 18 January 2007

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The response times of rotational molecular orientation of neat and carbon-nanotube-doped nematic liquid crystals were acquired through the measurement of transient current induced by a direct-current step voltage and from optical transmission data. A model based on the dielectric displacement current was developed to describe the electric field dependence of the response and to yield a rotational viscosity that would decrease with increasing concentration of carbon nanotubes. Optical dynamic response also showed a reduced rotational viscosity, with the lightly doped cells exhibiting a faster relaxation process than that of the neat cell.
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42.70.Df Liquid crystals
61.30.-v Liquid crystals
78.20.Jq Electro-optical effects

Fabrication of three-dimensional calixarene polymer waveguides using two-photon assisted polymerization

Jiro Ishihara, Kyoji Komatsu, Okihiro Sugihara, and Toshikuni Kaino

Appl. Phys. Lett. 90, 033511 (2007); http://dx.doi.org/10.1063/1.2430480 (3 pages) | Cited 9 times

Online Publication Date: 19 January 2007

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Low-loss three-dimensional (3D) polymer optical waveguide was fabricated using a two-photon assisted polymerization method. Calixarene derivatives were selected as core material with good thermal stability and transparency. To fabricate 3D waveguide, photopolymerizable polymers composed of two types of monomers were used. Core shape was controlled by adjusting an astigmatism of objective lens. Refractive index difference between a core and a cladding was formed by exclusion effect of one monomer. Propagation loss at 1.3 μm wavelength was low, 0.72 dB/cm, without using deuterium or fluorine but using hydrogen. Using this technique, 3D 1×3 splitter polymer waveguide was fabricated.
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42.79.Gn Optical waveguides and couplers
42.70.Jk Polymers and organics
42.79.Fm Reflectors, beam splitters, and deflectors

Organic photovoltaic devices with Ga-doped ZnO electrode

J. Owen, M. S. Son, K.-H. Yoo, B. D. Ahn, and S. Y. Lee

Appl. Phys. Lett. 90, 033512 (2007); http://dx.doi.org/10.1063/1.2432951 (3 pages) | Cited 36 times

Online Publication Date: 19 January 2007

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The authors report two organic photovoltaic devices using a Ga-doped ZnO (GZO) film as a transparent conducting electrode. In the first structure, the conventional In2O3:Sn hole-collecting anode was replaced by GZO and an efficiency of 0.35% was obtained. The second has the inverse structure where GZO was used as the electron-collecting cathode and gave a nonoptimized device efficiency of about 1.4%. Furthermore, this inverse structure of GZO devices provides a passivation layer to protect the active layer from the atmosphere.
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85.60.Bt Optoelectronic device characterization, design, and modeling

Highly efficient transparent organic light-emitting diodes by ion beam assisted deposition-prepared indium tin oxide cathode

Seung Yoon Ryu, Sang Hun Choi, Jong Tae Kim, Chang Su Kim, Hong Koo Baik, and Hee Seong Jeong

Appl. Phys. Lett. 90, 033513 (2007); http://dx.doi.org/10.1063/1.2433032 (3 pages) | Cited 10 times

Online Publication Date: 19 January 2007

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The authors have investigated the effects of indium tin oxide (ITO) deposited by ion beam assisted e-beam evaporation on the performance of polymer light-emitting diodes. ITO was evaporated as a cathode onto a thin Mg:Ag layer by an e-beam process, and its performance as a transparent cathode was subsequently compared to that of Mg:Ag and sputtering-prepared ITO. Polymer devices’ luminance and efficiency were improved by more than ten times by ion beam assisted deposition (IBAD)-prepared ITO deposition, with little observable damage to the organic layer. Implementation of the IBAD process resulted in the reduction of the interfacial energy barrier which induced band bending. Furthermore, outcoupling with ITO resulted in enhanced luminance.
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85.60.Jb Light-emitting devices

Efficient current injection scheme for nitride vertical cavity surface emitting lasers

A. Castiglia, D. Simeonov, H. J. Buehlmann, J.-F. Carlin, E. Feltin, J. Dorsaz, R. Butté, and N. Grandjean

Appl. Phys. Lett. 90, 033514 (2007); http://dx.doi.org/10.1063/1.2431484 (3 pages) | Cited 14 times

Online Publication Date: 19 January 2007

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The authors report the realization of InGaN/GaN light emitting diodes (LEDs) with an electrical injection design suitable for vertical cavity surface emitting lasers. Controlled oxidation of an AlInN interlayer lattice matched to GaN allows confining the injected current in a 3 μm diameter aperture. Submicron-scale characterization of the current flow and optical properties is achieved by means of microelectroluminescence measurements. LEDs can be safely driven, in continuous mode operation, up to current densities higher than 20 kA/cm2.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
85.60.Jb Light-emitting devices
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