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5 May 2003

Volume 82, Issue 18, pp. 2939-3130

Issue Cover Spotlight Figure

Appl. Phys. Lett. 82, 2957 (2003); http://dx.doi.org/10.1063/1.1571977 (3 pages)

Tadashi Kawazoe, Kiyoshi Kobayashi, Suguru Sangu, and Motoichi Ohtsu
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Organic donor/acceptor photovoltaics: The role of C60/metal interfaces

Christian Melzer, Victor V. Krasnikov, and Georges Hadziioannou

Appl. Phys. Lett. 82, 3101 (2003); http://dx.doi.org/10.1063/1.1570936 (3 pages) | Cited 11 times

Online Publication Date: 29 April 2003

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The photovoltaic properties of thin films based on donor/acceptor heterojunctions, prepared by means of either consecutive evaporation or co-evaporation, and sandwiched between asymmetric contacts are investigated. (E,E,E,E)-1,4-bis[(4-styryl)styryl]-2-methoxy-5-(2′-ethylhexoxy)benzene (MEH-OPV5) and Buckminster fullerene C60 are employed as donor and acceptor materials, respectively. Current-voltage measurements and impedance spectroscopy on the donor and the acceptor single-layer cells suggest the presence of a strong dipole layer at the C60/metal interfaces. The correlation between the photovoltaic performances and film morphologies is discussed. © 2003 American Institute of Physics.
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84.60.Jt Photoelectric conversion
73.40.Ns Metal-nonmetal contacts
68.55.-a Thin film structure and morphology
73.50.Pz Photoconduction and photovoltaic effects

Role of ultrathin Alq3 and LiF layers in conjugated polymer light-emitting diodes

X. Y. Deng, S. W. Tong, L. S. Hung, Y. Q. Mo, and Y. Cao

Appl. Phys. Lett. 82, 3104 (2003); http://dx.doi.org/10.1063/1.1571654 (3 pages) | Cited 16 times

Online Publication Date: 29 April 2003

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We report that an ultrathin layer of tris-(8-hydroxyquinoline) aluminum (Alq3) interposed between a bilayer cathode of LiF/Al and an emissive layer can significantly improve electroluminescence efficiency in a polymer light-emitting device (PLED). At a current density of 35 mA/cm2, a poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenyl-enevinylene] (MEH-PPV)-based PLED with a cathode of Alq3/LiF/Al has a quantum efficiency of 2.5%, considerably higher than that of a MEH-PPV-based PLED with a bare Al or a LiF/Al cathode. Interfacial characteristics of MEH-PPV/LiF/Al and MEH-PPV/Alq3/LiF/Al were investigated by photoelectron spectroscopy, and the results were used to explain the difference in device performance. © 2003 American Institute of Physics.
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85.60.Jb Light-emitting devices
79.60.Jv Interfaces; heterostructures; nanostructures

4H–SiC photoconductive switching devices for use in high-power applications

S. Dogan, A. Teke, D. Huang, H. Morkoç, C. B. Roberts, J. Parish, B. Ganguly, M. Smith, R. E. Myers, and S. E. Saddow

Appl. Phys. Lett. 82, 3107 (2003); http://dx.doi.org/10.1063/1.1571667 (3 pages) | Cited 20 times

Online Publication Date: 29 April 2003

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Silicon carbide is a wide-band-gap semiconductor suitable for high-power high-voltage devices and it has excellent properties for use in photoconductive semiconductor switches (PCSSs). PCSS were fabricated as planar structures on high-resistivity 4H–SiC and tested at dc bias voltages up to 1000 V. The typical maximum photocurrent of the device at 1000 V was about 49.4 A. The average on-state resistance and the ratio of on-state to off-state currents were about 20 Ω and 3×1011, respectively. Photoconductivity pulse widths for all applied voltages were 8–10 ns. These excellent results are due in part to the removal of the surface damage by high-temperature H2 etching and surface preparation. Atomic force microscopy images revealed that very good surface morphology, atomic layer flatness, and large step width were achieved. © 2003 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors
84.32.Dd Connectors, relays, and switches
73.61.Le Other inorganic semiconductors
85.30.Hi Surface barrier, boundary, and point contact devices
68.37.Ps Atomic force microscopy (AFM)
81.65.Cf Surface cleaning, etching, patterning
68.35.B- Structure of clean surfaces (and surface reconstruction)

Temperature dependence of gate–leakage current in AlGaN/GaN high-electron-mobility transistors

S. Arulkumaran, T. Egawa, H. Ishikawa, and T. Jimbo

Appl. Phys. Lett. 82, 3110 (2003); http://dx.doi.org/10.1063/1.1571655 (3 pages) | Cited 17 times

Online Publication Date: 29 April 2003

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We report on the studies of the temperature dependence of gate–leakage current in AlGaN/GaN high-electron-mobility transistors (HEMTs) for the temperature range 20–400 °C. The results show that the temperature dependence of gate–leakage current for AlGaN/GaN HEMTs at subthreshold regime (VGS = −6.5 V) have both negative and positive trends. It has been observed that the leakage current decreases with the temperature up to 80 °C. Above 80 °C, the leakage current increases with the temperature. The negative temperature dependence of leakage current with the activation energy +0.61 eV is due to the impact ionization. The positive temperature dependence of leakage current with the activation energy −0.20 eV is due to the surface related traps, and the activation energy −0.99 eV is due to the temperature assisted tunneling mechanism. The drain voltage at a fixed drain–leakage current reveals the occurrence of both positive (+0.28 V/K) and negative (−0.53 V/K) temperature coefficients. © 2003 American Institute of Physics.
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85.30.Tv Field effect devices

Influence of interfacial nitrogen on edge charge trapping at the interface of gate oxide/drain extension in metal–oxide–semiconductor transistors

T. P. Chen, J. Y. Huang, M. S. Tse, S. S. Tan, C. H. Ang, and S. Fung

Appl. Phys. Lett. 82, 3113 (2003); http://dx.doi.org/10.1063/1.1572471 (3 pages) | Cited 2 times

Online Publication Date: 29 April 2003

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In this work, the edge charge trapping at the interface of gate oxide/drain extension caused by Fowler–Nordheim injection is determined quantitatively by using a simple approach to analyze the change of the drain band-to-band tunneling current. For both pure and nitrided oxides with an oxide thickness of 6.5 nm, positive edge charge trapping is observed while the net charge trapping in the oxide above the channel is negative. It is found that the nitrogen at the interface can enhance the edge charge trapping. The results could be explained in terms of the creation of positive fixed oxide charges at the interface as a result of the electrochemical reactions involving holes and hydrogen ions. © 2003 American Institute of Physics.
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85.30.Tv Field effect devices

Photomixing and photoconductor measurements on ErAs/InGaAs at 1.55 μm

M. Sukhotin, E. R. Brown, A. C. Gossard, D. Driscoll, M. Hanson, P. Maker, and R. Muller

Appl. Phys. Lett. 82, 3116 (2003); http://dx.doi.org/10.1063/1.1567459 (3 pages) | Cited 29 times

Online Publication Date: 29 April 2003

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We report here the fabrication and demonstration of the photomixers made from In0.53Ga0.47As epitaxial material lattice-matched to InP. The material consists of layers of ErAs nanoparticles separated by InGaAs and compensated with Be to reduce the photocarrier lifetime to picosecond levels and to increase the resistivity to ∼100 Ω cm. Interdigitated-electrode and planar-antenna structures were fabricated by e-beam lithography and tested for dc electrical characteristics, 1.55-μm optical responsivity, and difference-frequency photomixing. The measured responsivity of 8 mA/W and photomixer output of >0.1 μW beyond 100 GHz are already comparable to GaAs photomixers and suggest that coherent THz generation is now feasible using the abundant 1.55-μm-semiconductor-laser and optical-fiber technologies. © 2003 American Institute of Physics.
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84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
84.40.-x Radiowave and microwave (including millimeter wave) technology
72.40.+w Photoconduction and photovoltaic effects
42.82.Cr Fabrication techniques; lithography, pattern transfer
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Surface-scattering effects in polycrystalline silicon thin-film transistors

A. Valletta, L. Mariucci, G. Fortunato, and S. D. Brotherton

Appl. Phys. Lett. 82, 3119 (2003); http://dx.doi.org/10.1063/1.1571960 (3 pages) | Cited 14 times

Online Publication Date: 29 April 2003

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Mobility reduction, induced at high gate fields by scattering with surface acoustic phonons and surface roughness, has been investigated in self-aligned polycrystalline silicon (polysilicon) thin-film transistors (TFTs). The analysis of this effect can be influenced by the presence of parasitic resistance effects, and a precise evaluation of this effect has been obtained by measuring the transfer characteristics in devices with different channel lengths. In this way, we could reliably determine the mobility reduction effect, which was then analyzed by using two-dimensional numerical simulations. The mobility reduction in polysilicon TFTs can be accurately described by Lombardi’s model, originally proposed for c-Si metal-oxide-semiconductor field-effect transistors. © 2003 American Institute of Physics.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling
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