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24 Oct 2005

Volume 87, Issue 17, Articles (17xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 87, 172506 (2005); http://dx.doi.org/10.1063/1.2120911 (3 pages)

T. Kimura, Y. Otani, and J. Hamrle
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High radiation tolerance of InAs/AlSb high-electron-mobility transistors

B. D. Weaver, J. B. Boos, N. A. Papanicolaou, B. R. Bennett, D. Park, and R. Bass

Appl. Phys. Lett. 87, 173501 (2005); http://dx.doi.org/10.1063/1.2115071 (3 pages) | Cited 7 times

Online Publication Date: 18 October 2005

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InAs/AlSb-based high-electron-mobility transistors (HEMTs) were irradiated with 2 MeV protons. Radiation damage caused the source-drain current Ids to decrease nearly linearly with fluence Φ at a rate of Δ[Ids(Φ)/Ids(0)]/ΔΦ ≈ 7×10−16 cm2. Radiation-induced decreases in Ids have been observed for other HEMT material systems, and have been attributed to high-efficiency defect-induced scattering of carriers out of the two-dimensional electron gas. However, in the InAs/AlSb system the rate of decrease of Ids is about 140 times less than that for typical GaAs/AlGaAs HEMTs. An explanation is presented in which the high radiation tolerance of InAs/AlSb HEMTs is related to carrier reinjection and the unusually large energy offset between the AlSb barriers and the InAs quantum well.
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85.30.Tv Field effect devices
61.80.Jh Ion radiation effects
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Ultraflexible organic field-effect transistors embedded at a neutral strain position

Tsuyoshi Sekitani, Shingo Iba, Yusaku Kato, Yoshiaki Noguchi, Takao Someya, and Takayasu Sakurai

Appl. Phys. Lett. 87, 173502 (2005); http://dx.doi.org/10.1063/1.2115075 (3 pages) | Cited 42 times

Online Publication Date: 18 October 2005

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We fabricated ultraflexible pentacene field-effect transistors (FETs) with a mobility of 0.5 cm2/V s and an on/off ratio of 105, which are functional at the bending radius less than 1 mm. The transistors are manufactured on a 13-μm-thick polyimide film and covered by a 13-μm-thick poly-chloro-para-xylylene encapsulation layer so that transistors can be embedded at a neutral position. This sandwiched structure can drastically suppress strain-induced changes in transistor characteristics. Furthermore, the FETs show no significant change after bending cycles of 60 000 times on inward and outward bending stresses.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Room-temperature reproducible spatial force spectroscopy using atom-tracking technique

M. Abe, Y. Sugimoto, O. Custance, and S. Morita

Appl. Phys. Lett. 87, 173503 (2005); http://dx.doi.org/10.1063/1.2108112 (3 pages) | Cited 57 times

Online Publication Date: 19 October 2005

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A method for reproducible site-specific force spectroscopic measurements using frequency modulation atomic force microscopy at room temperature is presented. The stability and reproducibility requirements, fulfilled so far only in cryogenic environment, are provided through the compensation of the thermal drift using the atom-tracking technique. The method has been tested performing spectroscopic measurements on atomic positions of the Si(111)-(7×7) surface with Si tips. The room-temperature results presented here compare in quality to previously reported quantitative force spectroscopic data obtained at cryogenic temperatures.
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68.47.Fg Semiconductor surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ps Atomic force microscopy (AFM)

Microbalance chemical sensor based on thin-film bulk acoustic wave resonators

M. Benetti, D. Cannatà, F. Di Pietrantonio, V. Foglietti, and E. Verona

Appl. Phys. Lett. 87, 173504 (2005); http://dx.doi.org/10.1063/1.2112187 (3 pages) | Cited 19 times

Online Publication Date: 19 October 2005

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An electroacoustic chemical sensor based on thin-film bulk acoustic wave resonators (TFBAR) is presented. It operates on the same principle of the well-known quartz crystal micro-balance, at an operation frequency extended up to several GHz. The larger output signal, associated to the higher operation frequency, is a condition to improve the device sensitivity. TFBARs have been implemented on (001) Si wafers, using Si3N4/AlN membranes, obtained by anisotropic etching of Si. Time response and calibration curves have been tested on TFBAR sensors exploiting two different chemically interactive membranes: Pd and Co-tetra-phenyl-porphyrin, both deposited in the form of thin-films by thermal evaporation. Measurements performed upon exposure to H2, CO, and ethanol have shown the ability of the device to detect low concentrations of the analyte with a fast and repeatable response.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
81.65.Cf Surface cleaning, etching, patterning

Efficient organic light-emitting diode using semitransparent silver as anode

Huajun Peng, Xiuling Zhu, Jiaxin Sun, Zhiliang Xie, Shuang Xie, Man Wong, and Hoi-Sing Kwok

Appl. Phys. Lett. 87, 173505 (2005); http://dx.doi.org/10.1063/1.2115076 (3 pages) | Cited 23 times

Online Publication Date: 19 October 2005

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A semitransparent silver layer is investigated as the anode for organic light-emitting devices (OLEDs). By pretreating the silver layer in a CF4 plasma, hole injection into the hole-transport layer is greatly enhanced. A bottom-emitting OLED using the modified, semitransparent silver anode, demonstrates improved current density-voltage characteristics and a 20% higher external quantum efficiency, compared to a conventional OLED using indium tin oxide as an anode. The superior optical characteristics are attributed to a higher outcoupling efficiency in the microcavity structure.
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85.60.Jb Light-emitting devices
85.60.Bt Optoelectronic device characterization, design, and modeling
52.77.-j Plasma applications

Methanofullerene-coated tetrabenzoporphyrin organic field-effect transistors

Patrick B. Shea, Jerzy Kanicki, Yong Cao, and Noboru Ono

Appl. Phys. Lett. 87, 173506 (2005); http://dx.doi.org/10.1063/1.2115077 (3 pages) | Cited 6 times

Online Publication Date: 19 October 2005

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Organic field-effect transistors (OFETs) using a solution-processable form of the organic semiconductor tetrabenzoporphyrin were fabricated with a top coating of a soluble n-type organic semiconductor. The top coating was found to extend the lifetime of the device in that the field-effect mobility, subthreshold slope, and OFF-state current were maintained at or near their as-fabricated states. Oxygen doping by extended air exposure was effectively slowed by the electron-accepting coating layer. Coated devices also display a transfer characteristic indicative of a parasitic latch-up transistor formed at the back channel of the OFETs.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling
61.72.up Other materials

Germanium n+/p junction formation by laser thermal process

Jidong Huang, Nan Wu, Qingchun Zhang, Chunxiang Zhu, Andrew A. O. Tay, Guoxin Chen, and Minghui Hong

Appl. Phys. Lett. 87, 173507 (2005); http://dx.doi.org/10.1063/1.2115078 (3 pages) | Cited 9 times

Online Publication Date: 19 October 2005

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In this letter, an n+/p junction on a germanium substrate, formed by phosphorous implantation and subsequent laser thermal annealing process, is demonstrated. The effects of laser energy fluence and irradiation pulse number on the redistribution of dopant atoms have been investigated. The secondary-ion-mass-spectrometry results indicate that steplike dopant profiles are formed with dopant atoms extending deeper upon increased laser energy fluence and successive pulse number. After being irradiated at a laser energy fluence of 0.16 J/cm2 with two successive pulses, the junction exhibits a sheet resistance of ∼ 50 Ohm/sq for n+ region, a comparable current-voltage characteristic, and much less phosphorus dopant diffusion in comparison with those formed by rapid thermal process annealing.
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61.72.Cc Kinetics of defect formation and annealing
61.72.uf Ge and Si
61.72.S- Impurities in crystals
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
66.30.J- Diffusion of impurities

Superconducting noise bolometer for terahertz radiation

A. D. Semenov, H. Richter, H.-W. Hübers, K. S. Il’in, and M. Siegel

Appl. Phys. Lett. 87, 173508 (2005); http://dx.doi.org/10.1063/1.2115086 (3 pages) | Cited 2 times

Online Publication Date: 19 October 2005

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We present a superconducting noise bolometer that is a bolometric detector sensing radiation via radiation-induced changes of its own microwave noise. The detector represents a nanostrip made from a thin NbN superconducting film. It operates in the superconducting state and carries a supercurrent slightly less than the critical current. Radiation couples with the detector via an immersion lens and a planar antenna, which jointly define the useful spectral range from 1 to 5 THz. At an ambient temperature of 4.2 K, the optically measured noise-equivalent power amounts at ≈ 10−13 W Hz−1/2 along with a time constant of approximately 150 ps.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors
74.78.-w Superconducting films and low-dimensional structures
84.40.Az Waveguides, transmission lines, striplines

Temperature-dependent carrier-transport and light-emission processes in a phosphorescent organic light-emitting device

Isao Tanaka and Shizuo Tokito

Appl. Phys. Lett. 87, 173509 (2005); http://dx.doi.org/10.1063/1.2117609 (3 pages) | Cited 8 times

Online Publication Date: 20 October 2005

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We report on carrier-transport, electroluminescence, and photoluminescence processes in a phosphorescent organic light-emitting device based on fac tris(2-phenylpyridine) iridium doped 4,4′-N,N′-dicarbazole-biphenyl over a wide temperature range from 5 to 295 K. The current flow could be described in terms of a space-charge-limited current with an exponential trap distribution at temperatures above 150 K. The electroluminescence intensity gradually decreased with decreasing temperature, whereas the photoluminescence intensity was almost independent of temperature. The difference between the temperature-dependent electroluminescence and photoluminescence intensities suggests that the carrier mobility depends on the electric field and the temperature.
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85.60.Jb Light-emitting devices

White organic light-emitting diodes based on tandem structures

Fawen Guo and Dongge Ma

Appl. Phys. Lett. 87, 173510 (2005); http://dx.doi.org/10.1063/1.2120898 (3 pages) | Cited 38 times

Online Publication Date: 21 October 2005

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White organic light-emitting diodes made of two electroluminescent (EL) units connected by a charge generation layer were fabricated. Thus, with a tandem structure of indium tin oxide/N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidine (NPB)/9,10-bis-(β-naphthyl)-anthrene (ADN)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)/tris(8-hydroxyquinoline) aluminum (Alq3)/BCP:Li/V2O5/NPB/Alq3:4-(dicyanomethylene)-2-t-butyle-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)4H-pyran (DCJTB)/Alq3/LiF/Al, a stable white light with Commission Internationale De L’Eclairage chromaticity coordinates from (0.35, 0.32) at 18 V to (0.36, 0.36) at 50 V was generated. It was clearly seen that the EL spectra consist of red band at 600 nm due to DCJTB, green band at 505 nm due to Alq3, and blue band at 435 nm due to ADN, and the current efficiency and brightness equal basically to the sum of the two EL units. As a result, the tandem devices showed white light emission with a maximum brightness of 10 200 cd/m2 at a bias of 40 V and a maximum current efficiency of 10.7 cd/A at a current density of 3.5 mA/cm2.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
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