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10 Oct 2005

Volume 87, Issue 15, Articles (15xxxx)

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Appl. Phys. Lett. 87, 151103 (2005); http://dx.doi.org/10.1063/1.2089157 (3 pages)

Andrew B. Greytak, Carl J. Barrelet, Yat Li, and Charles M. Lieber
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Spin-wave logical gates

M. P. Kostylev, A. A. Serga, T. Schneider, B. Leven, and B. Hillebrands

Appl. Phys. Lett. 87, 153501 (2005); http://dx.doi.org/10.1063/1.2089147 (3 pages) | Cited 72 times

Online Publication Date: 3 October 2005

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A universal approach to spin-wave logic gates is presented. The feasibility of a spin-wave based NOT gate has been demonstrated experimentally. We propose to use a Mach–Zender-type current-controlled interferometer based on spin-wave propagation in a ferromagnetic film to construct logical gates. We investigate the performance of the main element of such interferometric logical gates—the controlled phase shifter implemented as a spin-wave device.
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84.30.Sk Pulse and digital circuits

Photoreflectance investigations of a donor-related transition in AlGaN/GaN transistor structures

R. Kudrawiec, M. Syperek, J. Misiewicz, M. Rudziński, A. P. Grezegorczyk, P. R. Hageman, and P. K. Larsen

Appl. Phys. Lett. 87, 153502 (2005); http://dx.doi.org/10.1063/1.2084332 (3 pages) | Cited 5 times

Online Publication Date: 3 October 2005

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Below-bandgap photoreflectance (PR) features observed for GaN layers and undoped AlGaN/GaN transistor structures have been analyzed in this letter. In addition to PR signal associated with the interference oscillations a strong PR feature at ∼ 3.37 eV has been resolved for some AlGaN/GaN structures. This feature has been attributed to an electron transition between the valence band and a donorlike state located ∼ 50 meV below the conduction band. An absorptiontype experiment, such as PR spectroscopy, makes it possible to observe such a transition because this donorlike state is ionized by the strong internal electric field existing in the GaN layer at the AlGaN/GaN interface. The existence of this electric field with a magnitude of ∼ 210 kV/cm has been confirmed by the observation of GaN-related Franz-Keldysh oscillations in the PR spectra. Obtained results show that donorlike states located ∼ 50 meV below the conduction band are one of the sources of high concentration of the two dimensional electron gas in undoped AlGaN/GaN transistor structures.
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78.20.Jq Electro-optical effects
78.20.−e
71.55.−i

Deep level emission from high-power diode laser bars detected by multispectral infrared imaging

Anna Kozlowska, Piotr Wawrzyniak, Jens W. Tomm, Fritz Weik, and Thomas Elsaesser

Appl. Phys. Lett. 87, 153503 (2005); http://dx.doi.org/10.1063/1.2089150 (3 pages) | Cited 11 times

Online Publication Date: 5 October 2005

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Broadband imaging thermography is applied to investigate the infrared (IR) emission from high-power diode laser bars. We demonstrate the capabilities of a multispectral imaging system that operates in two optical channels, the near IR at 1.5–2 μm and the mid IR at 2.4–5.5 μm. In the near-IR region, deep level luminescence of the device contributes significantly to the thermo-images. A complementary measurement of the IR emission spectrum shows a broad defect band with maxima at E1 = 0.94 eV and E2 = 1.05 eV. Analysis of IR transients in both spectral channels makes a distinction of thermal radiation and deep level emission possible. In the mid IR, thermal radiation dominates, allowing for an analysis of thermal properties of the device with measurement times of fractions of a second only. This makes imaging thermography highly attractive for device screening.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
42.55.Px Semiconductor lasers; laser diodes
42.79.Pw Imaging detectors and sensors
78.55.Cr III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
78.67.De Quantum wells
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects

ZnO devices: Photodiodes and p-type field-effect transistors

Y. R. Ryu, T. S. Lee, J. A. Lubguban, H. W. White, Y. S. Park, and C. J. Youn

Appl. Phys. Lett. 87, 153504 (2005); http://dx.doi.org/10.1063/1.2089176 (3 pages) | Cited 62 times

Online Publication Date: 5 October 2005

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The potential use of ZnO-based photonic and electronic devices has been demonstrated by the fabrication of prototype ultraviolet (UV) photodetector and field-effect transistor (FET) devices that contain films of p-type ZnO with arsenic as the p-type dopant. These p-type films have high crystalline quality and show long-term stability. The ZnO UV photodetectors are based on p-n junctions. The FETs are made with metal-semiconductor Schottky contacts on p-type ZnO and are normally off (enhancement) devices. The spectral and electrical characteristics of these devices are presented and explained.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.30.Tv Field effect devices
85.60.Gz Photodetectors (including infrared and CCD detectors)

Measurement of the magnetoelectric coefficient using a scanning evanescent microwave microscope

Chen Gao, Bo Hu, Xuefei Li, Chihui Liu, M. Murakami, K.-S. Chang, C. J. Long, M. Wuttig, and I. Takeuchi

Appl. Phys. Lett. 87, 153505 (2005); http://dx.doi.org/10.1063/1.2093925 (3 pages) | Cited 4 times

Online Publication Date: 6 October 2005

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A quantitative magnetoelectric coefficient measurement method was developed based on scanning evanescent microwave microscopy. This unique technique does not require electrodes and has advantages that it has a high spatial resolution and can simultaneously measure other related properties such as the nonlinear dielectric constant. We have demonstrated that this technique can detect the magnetoelectric coefficient of thin film samples as low as 10 mV/cm Oe.
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75.80.+q Magnetomechanical effects, magnetostriction
77.22.Ch Permittivity (dielectric function)
77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
75.50.Dd Nonmetallic ferromagnetic materials

Control of threshold voltage in pentacene thin-film transistors using carrier doping at the charge-transfer interface with organic acceptors

Y. Abe, T. Hasegawa, Y. Takahashi, T. Yamada, and Y. Tokura

Appl. Phys. Lett. 87, 153506 (2005); http://dx.doi.org/10.1063/1.2099540 (3 pages) | Cited 44 times

Online Publication Date: 6 October 2005

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Well-controlled carrier doping was performed in pentacene thin-film transistors (TFTs) by depositing additional organic acceptor (F4TCNQ) layers on top of existing channels. The doping concentration could be predefined by changing the area covered with the acceptor layer, which provides control of the threshold gate voltage, while keeping both the field-effect mobility ( ∼ 1.0 cm2/V s) and the current on/off ratio (>105). The transport properties of these devices are discussed in terms of the trap and release model for the doped organic TFTs.
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85.30.Tv Field effect devices
85.40.Ry Impurity doping, diffusion and ion implantation technology
73.50.Dn Low-field transport and mobility; piezoresistance
73.61.Ph Polymers; organic compounds

Cu and CdCl2 influence on defects detected in CdTe solar cells with admittance spectroscopy

Fred H. Seymour, Victor Kaydanov, Tim R. Ohno, and David Albin

Appl. Phys. Lett. 87, 153507 (2005); http://dx.doi.org/10.1063/1.2099515 (3 pages) | Cited 10 times

Online Publication Date: 6 October 2005

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Admittance spectroscopy was used with a custom built temperature stage to study deep level defects in four polycrystalline thin-film CdTe solar cells that had postdeposition back contact treatments with and without Cu and CdCl2. One hole trap signature with activation energy Ea ≈ 0.13 eV was detected in all four cells and was attributed to a combination of VCd− and related complexes. A second hole trap with Ea ≈ 0.30 eV and detected only in Cu-treated cells was attributed to CuCd−. A third hole trap with Ea ≈ 0.47 eV was detected only in non-Cu-treated cells. The relationships and relative concentrations between these distinct trap levels are discussed.
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84.60.Jt Photoelectric conversion
71.55.Gs II-VI semiconductors

Vanadium pentoxide modified polycrystalline silicon anode for active-matrix organic light-emitting diodes

X. L. Zhu, J. X. Sun, H. J. Peng, Z. G. Meng, M. Wong, and H. S. Kwok

Appl. Phys. Lett. 87, 153508 (2005); http://dx.doi.org/10.1063/1.2099520 (3 pages) | Cited 34 times

Online Publication Date: 6 October 2005

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Recently, polycrystalline silicon (p-Si) has been demonstrated to be an efficient anode for organic light-emitting diode (OLED) [ X. L. Zhu, J. X. Sun, H. J. Peng, Z. G. Meng, M. Wong, and H. S. Kwok, Appl. Phys. Lett. 87, 083504 (2005) ]. In this letter, we show that, by depositing an ultrathin vanadium pentoxide (V2O5) layer on the p-Si anode, the performance of the OLED can be greatly improved. Detailed x-ray photoelectron spectroscopy study shows that strong band bending occurs at the p-Si/V2O5 interface, leading to much stronger hole injection. This modified p-Si anode can be integrated with the active p-Si layer of thin-film transistors in active-matrix OLED displays.
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85.60.Jb Light-emitting devices
82.45.Fk Electrodes
79.60.-i Photoemission and photoelectron spectra

High-efficiency inverted top-emitting polymer light-emitting diodes

Lintao Hou, Fei Huang, Wenjin Zeng, Junbiao Peng, and Yong Cao

Appl. Phys. Lett. 87, 153509 (2005); http://dx.doi.org/10.1063/1.2099528 (3 pages) | Cited 22 times

Online Publication Date: 6 October 2005

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A major challenge to inverted top-emitting polymer light-emitting diodes (ITEPLEDs) is to prepare a reflective bottom cathode capable of effectively injecting electrons. Reported in this letter is the creation of an efficient electron injection layer (EIL) by using environment-friendly alcohol-/water-soluble aminoalkyl-substituted conjugated quanternized polyfluorene copolymers containing 0.5% mol of benzothiadiazole to reduce the electron injection barrier between the high-work-function Al reflective bottom cathode and the light-emitting layer. The inverted top-emitting devices exhibit superior electrical characteristics with maximal quantum and luminance efficiencies of 2.71% and 1.6 cd/A respectively, at an operating voltage of 13.3 V by employing poly[2-methoxy,5-(2-ethylhexyloxy)-1,4-phenylenevinylene] as a light-emitting polymer. The utilization of water/alcohol soluble conjugated polyelectrolyte/Al bilayer bottom cathode offers an important advantage for avoiding intermixing between the emitting layer and the EIL for solution-processable ITEPLEDs.
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85.60.Jb Light-emitting devices
42.70.Jk Polymers and organics
82.45.Fk Electrodes

Effective channel length measurement of metal-oxide-semiconductor transistors with pocket implant using the subthreshold current-voltage characteristics based on remote Coulomb scattering

C. W. Eng, W. S. Lau, D. Vigar, S. S. Tan, and L. Chan

Appl. Phys. Lett. 87, 153510 (2005); http://dx.doi.org/10.1063/1.2093943 (3 pages) | Cited 7 times

Online Publication Date: 7 October 2005

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For deep submicron metal-oxide-semiconductor (MOS) transistors with pocket implant, the electron mobility of the short channel transistor is always smaller than that of the long channel transistor in the above-threshold regime, resulting in serious error in effective channel length (Leff) measurement based on the assumption that the mobility is independent of gate length. Our theory predicts that when the gate oxide is very thin the electron mobility is approximately equal for short and long channel MOS transistors in the subthreshold regime. Thus it is possible to perform Leff measurement in the subthreshold region of MOS transistors with ultrathin gate oxide.
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85.30.Tv Field effect devices
73.50.Dn Low-field transport and mobility; piezoresistance
85.30.De Semiconductor-device characterization, design, and modeling

Double-gate organic field-effect transistor

M. Morana, G. Bret, and C. Brabec

Appl. Phys. Lett. 87, 153511 (2005); http://dx.doi.org/10.1063/1.2103403 (3 pages) | Cited 17 times

Online Publication Date: 7 October 2005

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We present a novel double-gate structure for polymeric field-effect transistors produced from a solution of [9,9]-dioctylfluorene-co-bithiophene copolymer (F8T2) as the p-type organic semiconductor. The double-gate geometry adapts to different bias configurations and shows improved performances and higher flexibility of operation with respect to single-gate devices. The device characteristics show an increased on/off ratio and demonstrate the possibility to control the threshold voltage as well as the off current. The maximum hole mobility of 8×10−2 cm2/V s measured for the F8T2 layer, in combination with the features of the double-gate structure, suggest the possibility to produce optimized devices with very high performances.
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85.30.Tv Field effect devices
73.61.Ph Polymers; organic compounds
73.50.Dn Low-field transport and mobility; piezoresistance
72.20.Ee Mobility edges; hopping transport
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