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14 Feb 2005

Volume 86, Issue 7, Articles (07xxxx)

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Appl. Phys. Lett. 86, 071101 (2005); http://dx.doi.org/10.1063/1.1862756 (3 pages)

Robert Horvath, Henrik C. Pedersen, Nina Skivesen, David Selmeczi, and Niels B. Larsen
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Electron-hopping modes in NiMn2O4+δ materials

R. Schmidt, A. Basu, A. W. Brinkman, Z. Klusek, and P. K. Datta

Appl. Phys. Lett. 86, 073501 (2005); http://dx.doi.org/10.1063/1.1866643 (3 pages) | Cited 14 times

Online Publication Date: 7 February 2005

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The resistance versus temperature (R–T) characteristics of NiMn2O4+δ thermistors have been analyzed. In the literature, electron transport in manganate spinels is commonly described by a small-polaron model for nearest neighbor hopping, but variable range hopping (VRH) has not been considered so far. In this study differentiated R–T data were analyzed, allowing a clear distinction between different modes of hopping. In pressed pellets and thick screen printed films conduction was well described by a VRH model for a parabolic density of states, which was confirmed by scanning tunneling spectroscopy.
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84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)
72.20.Ee Mobility edges; hopping transport
73.20.At Surface states, band structure, electron density of states
72.20.Fr Low-field transport and mobility; piezoresistance
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Resonant tunneling in (110) oriented interband diodes

J. J. Zinck, D. H. Chow, K. S. Holabird, J. N. Schulman, K. C. Hall, and T. F. Boggess

Appl. Phys. Lett. 86, 073502 (2005); http://dx.doi.org/10.1063/1.1862335 (3 pages)

Online Publication Date: 7 February 2005

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Growth of high-quality Sb-based resonant tunneling diodes in the (110) orientation is demonstrated. The room-temperature current–voltage characteristics of the diodes are studied as a function of GaSb well width. Electronic band structure calculations including spin support the conclusion that the position of the GaSb light hole band with respect to the InAs conduction band is responsible for the strength of the negative differential resistance observed. The spin splitting of the heavy hole band is calculated to be larger than the light hole band suggesting that the observation of negative differential resistance may not be necessary or desirable for spin transport in these structures.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.30.Kk Junction diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.63.Hs Quantum wells
73.40.Gk Tunneling
73.21.Fg Quantum wells

Modeling of high-current source-gated transistors in amorphous silicon

F. Balon, J. M. Shannon, and B. J. Sealy

Appl. Phys. Lett. 86, 073503 (2005); http://dx.doi.org/10.1063/1.1865348 (3 pages) | Cited 7 times

Online Publication Date: 8 February 2005

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Compared with the field-effect transistor, the source-gated transistor has a much lower saturation voltage and higher output impedance. These features are investigated using computer modeling for amorphous silicon transistors operated at high currents when source barriers are low. In particular, it is shown that low saturation voltages are maintained at high current and are insensitive to source-drain separation. Furthermore, the output impedance is preserved even for submicron source-drain separations.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

pH sensors based on hydrogenated diamond surfaces

Jose A. Garrido, Andreas Härtl, Stefan Kuch, Martin Stutzmann, Oliver A. Williams, and R. B. Jackmann

Appl. Phys. Lett. 86, 073504 (2005); http://dx.doi.org/10.1063/1.1866632 (3 pages) | Cited 45 times

Online Publication Date: 9 February 2005

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We report on the operation of ungated surface conductive diamond devices in electrolytic solutions. The effect of electrolyte pH on the channel conductivity is studied in detail. It is shown that fully hydrogen terminated diamond surfaces are not pH sensitive. However, a pronounced pH sensitivity arises after a mild surface oxidation by ozone. We propose that charged ions from the electrolyte adsorbed on the oxidized surface regions induce a lateral electrostatic modulation of the conductive hole accumulation layer on the surface. In contrast, charged ions are not expected to be adsorbed on the hydrogen terminated surface, either due to the screening induced by a dense layer of strongly adsorbed counter-ions or by the absence of the proper reactive surface groups. Therefore, the modulation of the surface conductivity is generated by the oxidized regions, which are described as microscopic chemical in-plane gates. The pH sensitivity mechanism proposed here differs qualitatively from the one used to explain the behavior of conventional ion sensitive field effect transistors, resulting in a pH sensitivity higher than the Nernstian limit.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.-d Chemical analysis and related physical methods of analysis
85.30.Tv Field effect devices
81.65.Mq Oxidation
82.45.Gj Electrolytes
73.25.+i Surface conductivity and carrier phenomena

Polymer thin-film transistors fabricated by dry transfer of polymer semiconductor

Joonhyung Park, Sang-Oak Shim, and Hong H. Lee

Appl. Phys. Lett. 86, 073505 (2005); http://dx.doi.org/10.1063/1.1865347 (3 pages) | Cited 8 times

Online Publication Date: 9 February 2005

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A dry transfer technique is applied to the semiconductor layer formation in fabricating polymer thin-film transistors (TFTs). This method removes the solvent compatibility problem that is typically encountered in solution processing of polymer semiconductor and polymer gate dielectric such that any pair of the two polymers can be admitted to the fabrication of polymer TFTs. When the technique is used in place of spin coating of the active layer, the mobility increases by almost an order of magnitude, primarily because the deleterious effects are removed that a solvent can have on the underlying dielectric layer. Annealing of the active layer is also made possible by the method, which results in a significant improvement in the on∕off ratio of the device.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer
61.72.Cc Kinetics of defect formation and annealing
73.50.Dn Low-field transport and mobility; piezoresistance

1/f noise in gold nanoparticle chemosensors

C. Kurdak, J. Kim, A. Kuo, J. J. Lucido, L. A. Farina, X. Bai, M. P. Rowe, and A. J. Matzger

Appl. Phys. Lett. 86, 073506 (2005); http://dx.doi.org/10.1063/1.1865324 (3 pages) | Cited 8 times

Online Publication Date: 9 February 2005

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We present a systematic study of low-frequency noise in Au nanoparticle chemosensors. All the sensors we have studied exhibit 1/f-type noise at low frequencies. The magnitude of the 1/f noise was smaller in devices with a larger device area, indicating that the 1/f noise is caused by intrinsic processes. The noise amplitude was found to be strongly temperature dependent between 40–300 K, with a local peak at around 100 K, and weakly dependent below 40 K. The noise data could not be fit by a single activated process indicating that multiple noise processes must be present in our sensors.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.-d Chemical analysis and related physical methods of analysis
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
73.50.Td Noise processes and phenomena

Passive-matrix addressing of viologen–TiO2 displays

M. O. M. Edwards

Appl. Phys. Lett. 86, 073507 (2005); http://dx.doi.org/10.1063/1.1865334 (3 pages) | Cited 3 times

Online Publication Date: 9 February 2005

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The electric driving of 3×3 electrochromic passive-matrix displays, based on porous TiO2 films with surface-attached viologen molecules, is studied. A nonuniform contrast between dark and light pixels is obtained by a well-known addressing method for liquid-crystal passive-matrix displays. An alternative addressing method is developed. The method is capable of displaying arbitrary image patterns with uniform contrast.
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42.79.Kr Display devices, liquid-crystal devices

Photovoltaic hysteresis and its ramifications for concentrator solar cell design and diagnostics

Jeffrey M. Gordon, Eugene A. Katz, Wondesen Tassew, and Daniel Feuermann

Appl. Phys. Lett. 86, 073508 (2005); http://dx.doi.org/10.1063/1.1862776 (3 pages) | Cited 10 times

Online Publication Date: 10 February 2005

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We report the observation of a photovoltaic effect with pronounced hysteresis. The phenomenon derives from the sharp transition in the dominant mode of electron transport in the tunnel diodes that regulate multijunction solar cells, and is only observable at high flux. These results emerged from measurements of cell current-voltage characteristics performed with miniature fiber-optic solar concentrators that can deliver flux levels up to 10 000 times that of ambient sunlight in a highly localized fashion. The ramifications of our findings for photovoltaic design, diagnostics, and performance are addressed, and a nondestructive determination of the peak and valley threshold current densities of tunnel diodes is presented.
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84.60.Jt Photoelectric conversion
42.79.Ek Solar collectors and concentrators
72.40.+w Photoconduction and photovoltaic effects
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Negative capacitance in organic light-emitting diodes

L. S. C. Pingree, B. J. Scott, M. T. Russell, T. J. Marks, and M. C. Hersam

Appl. Phys. Lett. 86, 073509 (2005); http://dx.doi.org/10.1063/1.1865346 (3 pages) | Cited 30 times

Online Publication Date: 10 February 2005

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Negative capacitance has been characterized in organic light-emitting diode (OLED) heterostructures using impedance spectroscopy. Although similar inductive behavior has been previously reported for transient electroluminescence in OLEDs, definitive identification of negative capacitance in impedance spectroscopy data has been elusive due to the high concentration of distributed traps at the anode-organic interface. The addition of a layer of 4,4′-bis[(p-trichlorosilylpropylphenyl)phenylamino]-biphenyl at this interface minimizes these trapping sites, thus enabling the inductive nature of charge transport in OLEDs to be directly observable. By quantitatively correlating the resulting impedance spectroscopy data with equivalent circuit models, a detailed description of charge transport in OLEDs as a function of heterostructure composition is developed.
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85.60.Jb Light-emitting devices
85.30.De Semiconductor-device characterization, design, and modeling
73.61.Ph Polymers; organic compounds

White organic light-emitting diodes prepared by a fused organic solid solution method

Yan Shao and Yang Yang

Appl. Phys. Lett. 86, 073510 (2005); http://dx.doi.org/10.1063/1.1866216 (3 pages) | Cited 39 times

Online Publication Date: 10 February 2005

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This letter demonstrates a white organic light-emitting diode (OLED) with high color stability fabricated by using a single organic white-emitting layer. The dopants were introduced prior to the device fabrication process through organic solid solution process formed by high-temperature and high-pressure fusion process. A high band gap organic material, α-naphthlyphenylbiphenyl diamine, was adopted and precisely doped with several kinds of fluorescent dyes as the emitting material. The most important benefits of using this fused organic solid-solution technique are the precise control of dopants, ultrauniform mixture of dopants in the host, easy fabrication; and, as a result, the fabricated white OLEDs show extremely little color shift with increasing injection current. The simplified device fabrication process is believed to be beneficial to the white OLED display and lighting industrialization.
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85.60.Jb Light-emitting devices
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
73.61.Ph Polymers; organic compounds
78.66.Qn Polymers; organic compounds
68.55.A- Nucleation and growth
78.60.Fi Electroluminescence
73.50.Dn Low-field transport and mobility; piezoresistance

Bending experiment on pentacene field-effect transistors on plastic films

Tsuyoshi Sekitani, Yusaku Kato, Shingo Iba, Hiroshi Shinaoka, Takao Someya, Takayasu Sakurai, and Shinichi Takagi

Appl. Phys. Lett. 86, 073511 (2005); http://dx.doi.org/10.1063/1.1868868 (3 pages) | Cited 25 times

Online Publication Date: 11 February 2005

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We have fabricated very flexible pentacene field-effect transistors with polyimide gate dielectric layers on plastic films with a mobility of 0.3 cm2/V s and an on/off ratio of 105, and have measured their electrical properties under various compressive and tensile strains while changing the bending radius of the base plastic films systematically. We have found that the change in source-drain current with bending radius is reproducible and reversible when the bending radius is above 4.6 mm, which corresponds to strains of ∼ 1.4±0.1%. Furthermore, the change in source-drain current does not depend on the direction of strain versus direction of current flow.
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85.30.Tv Field effect devices
73.50.Dn Low-field transport and mobility; piezoresistance
81.40.Lm Deformation, plasticity, and creep
68.60.Bs Mechanical and acoustical properties
62.20.F- Deformation and plasticity
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