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7 Nov 2005

Volume 87, Issue 19, Articles (19xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 87, 192502 (2005); http://dx.doi.org/10.1063/1.2128478 (3 pages)

Ki-Suk Lee, SangKook Choi, and Sang-Koog Kim
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Enhancement of iridium-based organic light-emitting diodes by spatial doping of the hole transport layer

Ying Wang, Weiying Gao, Slawomir Braun, William R. Salaneck, Fabrice Amy, Calvin Chan, and Antoine Kahn

Appl. Phys. Lett. 87, 193501 (2005); http://dx.doi.org/10.1063/1.2117623 (3 pages) | Cited 6 times

Online Publication Date: 31 October 2005

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The electroluminescence efficiency of Ir-based green emitter devices is very sensitive to the nature of the hole transport layer used. We show that by inserting a 1 nm layer of bis[4-(N,N-diethylamino)-2-methylphenyl](4-methylphenyl)methane (MPMP) in a 4,4′-bis-(carbazol-9-yl)biphenyl (CBP) hole transport layer, a device that combines the positive attributes of both MPMP (high efficiency) and CBP (low injection voltage) is obtained. These results can be understood based on a combined ultraviolet photoemission spectroscopy/inverse photoemission spectroscopy study, which reveals the very low electron affinity and superior electron blocking capability of MPMP.
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85.60.Jb Light-emitting devices

Efficient white-light-emitting diodes based on polymer codoped with two phosphorescent dyes

Yunhua Xu, Junbiao Peng, Jiaxing Jiang, Wei Xu, Wei Yang, and Yong Cao

Appl. Phys. Lett. 87, 193502 (2005); http://dx.doi.org/10.1063/1.2119407 (3 pages) | Cited 63 times

Online Publication Date: 1 November 2005

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Efficient white-light-emitting diodes (WPLEDs) based on a polymer codoped with two phosphorescent dyes were fabricated by the spin-casting method. Polyhedral oligomeric silsesquioxane-terminated poly(9,9-dioctylfluorene) (PFO-poss) was used as the host and blue light emitter. Phosphorescent emitters, fac-tris[2-(4′-ter-butyl)phenylpyridine] iridium (III) [Ir(Bu-ppy)3] and bis-(1-phenylisoquinolyl)iridium(III)(1-trifluoro) acetylacetonate [(Piq)2Ir(acaF)] with green and red emission, respectively, were used as the guests. The electroluminescence spectrum can be tuned by changing concentration of the guests. The structure of the WPLEDs is indium tin oxide (ITO)/poly(ethlenedioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS)/ PVK/PFO-poss codoped with Ir(Bu-ppy)3 and (Piq)2Ir(acaF)/Ba/Al. The PVK layer [poly(N-vinylcarbazole)] acts as the function of blocking electron penetrating from PFO-poss to PEDOT. When the doping concentrations are 0.14 wt % for both Ir(Bu-ppy)3 and (Piq)2Ir(acaF), the efficient white-light emission with CIE coordinates of around (0.33, 0.33) is achieved. The current efficiency reaches 5.5 lm/W (9 cd/A), and the maximum luminance of 10 200 cd/m2 was gained at 11 V. The mechanisms of the WPLEDs with high efficiency are discussed.
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85.60.Jb Light-emitting devices
78.55.Kz Solid organic materials
78.60.Fi Electroluminescence
61.72.S- Impurities in crystals
61.72.up Other materials

High-performance flexible zinc tin oxide field-effect transistors

W. B. Jackson, R. L. Hoffman, and G. S. Herman

Appl. Phys. Lett. 87, 193503 (2005); http://dx.doi.org/10.1063/1.2120895 (3 pages) | Cited 75 times

Online Publication Date: 1 November 2005

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Flexible transistors were fabricated by sputter deposition of zinc tin oxide (ZTO) onto plasma-enhanced chemical vapor deposition gate dielectrics formed on flexible polyimide substrates with a blanket aluminum gate electrode. The flexible transistors exhibited high on-currents of 1 mA, on/off ratios of 106, subthreshold voltage slopes of 1.6 V/decade, turn-on voltages of −17 V, and mobilities of 14 cm2 V−1 s−1. Capacitance measurements indicate that the threshold voltage and subthreshold slope are primarily influenced by residual doping in the ZTO rather than by defects at the semiconductor/dielectric interface, and are useful for assessing contact resistance.
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85.30.Tv Field effect devices
61.72.uj III-V and II-VI semiconductors

Low-power memory device with NiSi2 nanocrystals embedded in silicon dioxide layer

P. H. Yeh, C. H. Yu, L. J. Chen, H. H. Wu, P. T. Liu, and T. C. Chang

Appl. Phys. Lett. 87, 193504 (2005); http://dx.doi.org/10.1063/1.2126150 (3 pages) | Cited 18 times

Online Publication Date: 2 November 2005

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A metal-oxide-semiconductor structure with NiSi2 nanocrystals embedded in the SiO2 layer has been fabricated. A pronounced capacitance-voltage hysteresis was observed with a memory window of 1 V under the 2 V programming voltage. The processing of the structure is compatible with the current manufacturing technology of semiconductor industry.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Photocurrent spectroscopy under depletion mode of transparent polymer field-effect transistors

S. Dutta and K. S. Narayan

Appl. Phys. Lett. 87, 193505 (2005); http://dx.doi.org/10.1063/1.2126151 (3 pages) | Cited 8 times

Online Publication Date: 2 November 2005

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The unique combination of voltage and light as the controlling parameters for charge transport in polymer-based field-effect transistors (PFETs) offers interesting strategies for light detection. Results of gate-voltage (Vg)-controlled intensity-modulated spectral response of the drain current in optically transparent PFETs are reported. The measurement and analysis of the results, obtained from light incident from the top and bottom side of the device, provide spatial information of the Vg-dependent photocarrier generation region. These measurements serve as a direct measure of the extent of the depletion.
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85.30.Tv Field effect devices
73.61.Ph Polymers; organic compounds

Optimal design of microscaled scattering optical elements

Andreas Håkansson and José Sánchez-Dehesa

Appl. Phys. Lett. 87, 193506 (2005); http://dx.doi.org/10.1063/1.2126134 (3 pages) | Cited 9 times

Online Publication Date: 2 November 2005

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A method of inverse design is applied to generate an optical device that acts as a wavelength demultiplexer. The ultracompact device, only 2 μm thick, is designed to separate two wavelengths 1.55 μm and 1.50 μm, respectively, and consists of five layers of 0.4 μm×0.4 μm square-shaped bars etched in gallium arsenide. The expected cross talk is suppressed below −25 dB for both wavelengths. The proposed device is an example of a scattering optical element, a name here introduced to define a class of computer-generated optical devices and whose functionalities are based on the multiple scattering by their individual constituents. For realization of the aforementioned devices, two-dimensional photonic plates can be prepared by only a single integrated circuit processing procedure followed by micromanipulation assembling.
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42.15.Eq Optical system design
84.40.Ua Telecommunications: signal transmission and processing; communication satellites
42.82.Bq Design and performance testing of integrated-optical systems

Single-quantum-well grating-gated terahertz plasmon detectors

E. A. Shaner, Mark Lee, M. C. Wanke, A. D. Grine, J. L. Reno, and S. J. Allen

Appl. Phys. Lett. 87, 193507 (2005); http://dx.doi.org/10.1063/1.2128057 (3 pages) | Cited 48 times

Online Publication Date: 2 November 2005

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A grating-gated field-effect transistor fabricated from a single-quantum well in a high-mobility GaAs–AlGaAs heterostructure is shown to function as a continuously electrically tunable photodetector of terahertz radiation via excitation of resonant plasmon modes in the well. Different harmonics of the plasmon wave vector are mapped, showing different branches of the dispersion relation. As a function of temperature, the resonant response magnitude peaks at around 30 K. Both photovoltaic and photoconductive responses have been observed under different incident power and bias conditions.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.30.Tv Field effect devices
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
72.40.+w Photoconduction and photovoltaic effects

High-performance organic thin-film transistors with metal oxide/metal bilayer electrode

Chih-Wei Chu, Sheng-Han Li, Chieh-Wei Chen, Vishal Shrotriya, and Yang Yang

Appl. Phys. Lett. 87, 193508 (2005); http://dx.doi.org/10.1063/1.2126140 (3 pages) | Cited 136 times

Online Publication Date: 3 November 2005

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We demonstrate bilayer source-drain (S-D) electrodes for organic thin film transistors (OTFT). The bilayer consists of a transition metal oxide (MoO3,WO3, or V2O5) layer and a metal layer. The metal oxide layer, directly contacting the organic semiconducting layer, serves as the charge-injection layer. The overcoated metal layer is responsible for the conduction of charge carriers. We found that the metal oxide layer coupled between pentacene and metal layers played an important role in improving the field-effect transistor characteristics of OTFTs. Devices with the bilayer S-D electrodes showed enhanced hole-injection compared to those with only metal electrode. High field-effect mobility of 0.4 cm2/V s and on/off current ratios of 104 were obtained in the pentacene based TFTs using the bilayer S-D electrodes at a gate bias of −40 V. The improvement is attributed to the reduction in the contact barrier and the prevention of metal diffusion into the organic layer and/or unfavorable chemical reaction between the organic layer and the metal electrode.
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85.30.Tv Field effect devices
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Double amorphous silicon-carbide p-layer structures producing highly stabilized pin-type protocrystalline silicon multilayer solar cells

Seung Yeop Myong, Koeng Su Lim, and Joshua M. Pears

Appl. Phys. Lett. 87, 193509 (2005); http://dx.doi.org/10.1063/1.2126802 (3 pages) | Cited 11 times

Online Publication Date: 3 November 2005

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We have applied double p-type amorphous silicon-carbide (p-a-SiC:H) layer structures to pin-type protocrystalline silicon (pc-Si:H) multilayer solar cells. The less-pronounced initial short-wavelength quantum efficiency variation against the biased voltage and the wide overlap of dark current—voltage (JD-V) and short-circuit current—open-circuit voltage (Jsc-Voc) characteristics prove that the double p-a-SiC:H layer structure successfully reduces recombination at the p/i interface. Therefore, we achieved highly stabilized efficiency of 9.0% without any backreflector.
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84.60.Jt Photoelectric conversion

Terahertz radiation from heavy-ion-irradiated In0.53Ga0.47As photoconductive antenna excited at 1.55 μm

N. Chimot, J. Mangeney, L. Joulaud, P. Crozat, H. Bernas, K. Blary, and J. F. Lampin

Appl. Phys. Lett. 87, 193510 (2005); http://dx.doi.org/10.1063/1.2126110 (3 pages) | Cited 32 times

Online Publication Date: 4 November 2005

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We investigate terahertz (THz) emission from heavy-ion-irradiated In0.53Ga0.47As photoconductive antennas excited at 1550 nm. The carrier lifetime in the highly irradiated In0.53Ga0.47As layer is less than 200 fs, the steady-state mobility is 490 cm2 V−1 s−1, and the dark resistivity is 3 Ω cm. The spectrum of the electric field radiating from the Br+-irradiated In0.53Ga0.47As antenna extends beyond 2 THz. The THz electric field magnitude is shown to saturate at high optical pump fluence, and the saturation fluence level increases with the irradiation dose, indicating that defect center scattering has a significant contribution to the transient mobility.
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84.40.Ba Antennas: theory, components and accessories
61.80.Jh Ion radiation effects
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