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12 Sep 2005

Volume 87, Issue 11, Articles (11xxxx)

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Appl. Phys. Lett. 87, 113902 (2005); http://dx.doi.org/10.1063/1.2045549 (3 pages)

M. Laroussi and X. Lu
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Electrode specific electropolymerization of ethylenedioxythiophene: Injection enhancement in organic transistors

Raoul Schroeder, Leszek A. Majewski, Martin Grell, Jonathan Maunoury, Julien Gautrot, Philip Hodge, and Mike Turner

Appl. Phys. Lett. 87, 113501 (2005); http://dx.doi.org/10.1063/1.2035879 (3 pages) | Cited 16 times

Online Publication Date: 6 September 2005

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In this letter, we report on a method of decreasing the injection barrier from metal electrodes to organic semiconductors, namely pentacene and poly(triarylamine) (PTAA). This method involves the electrodeposition of PEDOT∕PSS on to the source electrode of an organic field-effect transistor (OFET) without unintended doping of the channel. In an OFET, the drain current injected at the PEDOT∕PSS coated gold electrode increases (2–6) fold over that of the current injected at the unmodified gold electrode, all else being the same. Furthermore, in the transistor with a polytriarylamine as the semiconductor, a decrease of the threshold voltage is observed.
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85.30.Tv Field effect devices
81.15.Pq Electrodeposition, electroplating

Display device with dual emissive and reflective modes

X. J. Wang, W. M. Lau, and K. Y. Wong

Appl. Phys. Lett. 87, 113502 (2005); http://dx.doi.org/10.1063/1.2043249 (3 pages) | Cited 14 times

Online Publication Date: 7 September 2005

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A display device with dual electroluminescence and electrochromic display functions is described. The device consists of two layers of polymeric thin films, one of which is an electrochromic polymer and the other an electroluminescence polymer, that are sandwiched between two electrodes. Both polymers are blended with a solid electrolyte. The device functions as an electroluminescence device when positively biased, and as an electrochromic device if biased negatively instead. The measured current density for the electrochromic mode of operation was found to be two orders of magnitude lower than that for the electroluminescence mode. This functional duality demonstrates the successful combination of the option of light-emitting display and the power saving electrochromic mode for portable devices.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
42.79.Kr Display devices, liquid-crystal devices

The effect of interfacial layer on the performance of organic light-emitting diodes

Stelios A. Choulis, Vi-En Choong, Mathew K. Mathai, and Franky So

Appl. Phys. Lett. 87, 113503 (2005); http://dx.doi.org/10.1063/1.2042635 (3 pages) | Cited 73 times

Online Publication Date: 7 September 2005

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We demonstrate high efficiency organic light-emitting devices by incorporation of a nanoscale interfacial layer between a hole-conducting layer (PEDOT:PSS) and a light-emitting polymer layer (LEP) to improve hole injection. The interfacial layer has appropriate highest occupied molecular orbital level in order to act as a bridge for efficient hole injection from the PEDOT:PSS into the LEP. As an example we have incorporated a suitable interfacial layer into a green-emitting single-layer electrophosphorescent light-emitting diode. Devices with the interfacial layer show a peak efficiency of 41 lm/W, an improvement of more than 25% in their performance over comparable devices without the interfacial layer. The results presented here introduce a novel method to improve hole injection and thus efficiency in organic electroluminescent devices.
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85.60.Jb Light-emitting devices

Isobar suppression by photodetachment in a gas-filled rf quadrupole ion guide

Y. Liu, J. R. Beene, C. C. Havener, and J. F. Liang

Appl. Phys. Lett. 87, 113504 (2005); http://dx.doi.org/10.1063/1.2046732 (3 pages) | Cited 6 times

Online Publication Date: 8 September 2005

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A technique based on selective nonresonant laser photodetachment of unwanted negative ion species has been developed for efficient suppression of isobaric contaminants in negative ion beams. A radio-frequency quadrupole ion guide is employed to cool the negative ion beam and dramatically increase the interaction time of the ions with the laser, substantially increasing the efficiency of the photodetachment process. In a proof-of-principle experiment, we achieved 95% suppression of math ions by photodetachment while under identical conditions 10% of math ions were neutralized.
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32.80.Gc Photodetachment of atomic negative ions
07.75.+h Mass spectrometers
42.62.-b Laser applications
07.77.-n Atomic, molecular, and charged-particle sources and detectors

Complementary inverter based on interface doped pentacene

Marcus Ahles, Roland Schmechel, and Heinz von Seggern

Appl. Phys. Lett. 87, 113505 (2005); http://dx.doi.org/10.1063/1.2045556 (3 pages) | Cited 35 times

Online Publication Date: 9 September 2005

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An organic complementary metal–oxide–semiconductor (O-CMOS) inverter is presented, which is based on a single pentacene layer acting both as n- and p-type organic semiconductors. The circuit consists of two spatially separated transistors realized by pairs of calcium and gold source and drain electrodes, respectively. The p transistor is obtained by utilizing the conventional pentacene/SiO2 channel interface whereas the n transistor is realized by doping the SiO2 interface with traces of calcium prior to pentacene deposition. Both, n and p transistors work exclusively in unipolar mode within the range of the supply voltage of 60 V. The O-CMOS inverter works reliably with a gain in between 17 and 24, and the respective electron and hole mobilities were found around 0.1 cm2 V−1 s−1. The circuit shows hysteresis, which can be explained by a gate voltage-dependent electron trapping in the n channel. Electron accumulation can also be realized by the application of a polymethylmethacrylate interlayer between SiO2 and pentacene.
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85.30.Tv Field effect devices

Photovoltaic effect in poly-dioctyl-phenylene-ethynylene-C60 cells upon donor and acceptor excitation

A. G. Umnov and O. J. Korovyanko

Appl. Phys. Lett. 87, 113506 (2005); http://dx.doi.org/10.1063/1.2048817 (3 pages) | Cited 7 times

Online Publication Date: 9 September 2005

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We studied photovoltaic effect in poly-dioctyl-phenylene-ethynylene (PPE)-C60 cells using photovoltage and photocurrent spectroscopy. We observe two-step photoexcitation dependence of open circuit voltage Voc. Two values of Voc are due to different Coulomb binding energies for carriers originated from excitons in PPE and C60. Due to built-in potential between PPE and C60 layers, carriers overcome this exciton binding energy and separate at the heterojunction. We describe our results by energy diagram, comparing exciton binding energies in donor and acceptor moieties.
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85.60.Bt Optoelectronic device characterization, design, and modeling
85.65.+h Molecular electronic devices
72.40.+w Photoconduction and photovoltaic effects
71.35.-y Excitons and related phenomena
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Large deep-ultraviolet photocurrent in metal-semiconductor-metal structures fabricated on as-grown boron-doped diamond

Jose Alvarez, Meiyong Liao, and Yasuo Koide

Appl. Phys. Lett. 87, 113507 (2005); http://dx.doi.org/10.1063/1.2048807 (3 pages) | Cited 4 times

Online Publication Date: 9 September 2005

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Metal-semiconductor-metal planar devices have been fabricated on as-grown boron-doped homoepitaxial diamond thin films. They consist of two Schottky barriers connected back to back. The metal employed was a thin titanium (Ti) layer (5 nm) followed by a gold (Au) cap layer (50 nm), respectively. The structure shows a high ultraviolet photocurrent at 220 nm, which is seven orders of magnitude higher than the reverse dark current (<1 pA) for at least an applied voltage of ±0.4 V. In addition, anomalous photoconductivity gain is observed. A plausible explanation could be the modification of the Schottky barrier under band-to-band illumination. The spectral photoresponse displays over six orders of magnitude discrimination between deep-ultraviolet (210 nm) and visible light (630 nm), and reveals a shoulder with an onset at 4.6 eV.
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72.40.+w Photoconduction and photovoltaic effects
73.40.Sx Metal-semiconductor-metal structures
78.40.-q Absorption and reflection spectra: visible and ultraviolet
73.30.+y Surface double layers, Schottky barriers, and work functions
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