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2 Jul 2007

Volume 91, Issue 1, Articles (01xxxx)

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Appl. Phys. Lett. 91, 013501 (2007); http://dx.doi.org/10.1063/1.2753120 (3 pages)

J. Verd, A. Uranga, G. Abadal, J. Teva, F. Torres, F. Pérez-Murano, J. Fraxedas, J. Esteve, and N. Barniol
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Monolithic mass sensor fabricated using a conventional technology with attogram resolution in air conditions

J. Verd, A. Uranga, G. Abadal, J. Teva, F. Torres, F. Pérez-Murano, J. Fraxedas, J. Esteve, and N. Barniol

Appl. Phys. Lett. 91, 013501 (2007); http://dx.doi.org/10.1063/1.2753120 (3 pages) | Cited 17 times

Online Publication Date: 2 July 2007

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Monolithic mass sensors for ultrasensitive mass detection in air conditions have been fabricated using a conventional 0.35 μm complementary metal-oxide-semiconductor (CMOS) process. The mass sensors are based on electrostatically excited submicrometer scale cantilevers integrated with CMOS electronics. The devices have been calibrated obtaining an experimental sensitivity of 6×10−11 g/cm2 Hz equivalent to 0.9 ag/Hz for locally deposited mass. Results from time-resolved mass measurements are also presented. An evaluation of the mass resolution have been performed obtaining a value of 2.4×10−17 g in air conditions, resulting in an improvement of these devices from previous works in terms of sensitivity, resolution, and fabrication process complexity.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.30.Tv Field effect devices

Amorphous ZnO transparent thin-film transistors fabricated by fully lithographic and etching processes

Hsing-Hung Hsieh and Chung-Chih Wu

Appl. Phys. Lett. 91, 013502 (2007); http://dx.doi.org/10.1063/1.2753724 (3 pages) | Cited 57 times

Online Publication Date: 2 July 2007

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Oxide-semiconductor-based thin-film transistors (TFTs), particularly the amorphous ones, are becoming an important emerging technology. Since oxide semiconductors easily form polycrystalline phases, usually more complicated oxide mixtures are needed for growing amorphous phases. In this letter, we report that by simply reducing the thickness, ZnO can be intentionally grown into the amorphous phase. Furthermore, both top-gate and bottom-gate amorphous ZnO TFTs of micrometer scales were effectively implemented using fully lithographic and etching processes. Rather high field-effect mobilities of 25 and 4 cm2/V s and on∕off current ratios of >107 and >106 were achieved for top-gate and bottom-gate configurations, respectively.
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85.30.Tv Field effect devices

Enhancing the dot density in quantum dot infrared photodetectors via the incorporation of antimony

P. Aivaliotis, L. R. Wilson, E. A. Zibik, J. W. Cockburn, M. J. Steer, and H. Y. Liu

Appl. Phys. Lett. 91, 013503 (2007); http://dx.doi.org/10.1063/1.2753727 (3 pages) | Cited 18 times

Online Publication Date: 2 July 2007

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The authors combine optical spectroscopic studies and infrared photodetector development to demonstrate the potential of antimony-mediated InAs quantum dot growth for the production of high performance dot-based devices. By depositing 1 ML of gallium antimonide prior to dot growth, the dot density is increased from ∼ 3×1010 for conventional InAs dots, to ∼ 6×1010 cm−2. Detailed intra- and interband spectroscopic studies show no significant differences in the electron energy level configuration compared with standard InAs/GaAs dots, while intraband absorption strength is increased. Furthermore, they have implemented this growth technique to produce a quantum dot infrared photodetector with a detectivity of ∼ 5×1010 cm Hz1/2 W−1 at 7.5 μm (T = 77 K).
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Nitride-based light emitting diodes with indium tin oxide electrode patterned by imprint lithography

S. J. Chang, C. F. Shen, W. S. Chen, C. T. Kuo, T. K. Ko, S. C. Shei, and J. K. Sheu

Appl. Phys. Lett. 91, 013504 (2007); http://dx.doi.org/10.1063/1.2753726 (3 pages) | Cited 27 times

Online Publication Date: 3 July 2007

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The authors propose a simple, low cost, and mass producible imprint lithography method to texture indium tin oxide (ITO) contact layer of nitride-based light emitting diodes (LEDs). Under 20 mA current injection, it was found that forward voltages were 3.24, 3.25, and 3.24 V while the LED output powers were 11.7, 12.6, and 13.3 mW for the conventional ITO LED, ITO LED patterned with 1.75 μm holes, and ITO LED patterned with 0.85 μm holes, respectively.
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85.60.Jb Light-emitting devices

Using the temperature dependence of resonator quality factor as a thermometer

M. A. Hopcroft, B. Kim, S. Chandorkar, R. Melamud, M. Agarwal, C. M. Jha, G. Bahl, J. Salvia, H. Mehta, H. K. Lee, R. N. Candler, and T. W. Kenny

Appl. Phys. Lett. 91, 013505 (2007); http://dx.doi.org/10.1063/1.2753758 (3 pages) | Cited 13 times

Online Publication Date: 3 July 2007

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Silicon micromechanical resonators have been designed to have a quality factor (Q) that is a strong function of temperature. This is an ideal sensor for the temperature of the resonator—it is instantaneous, consumes no power, and indicates the temperature of the resonator structure with high sensitivity. The authors present a practical implementation of an oscillator system using these resonators with a temperature resolution of better than 0.002 °C. The Q(T) signal is uniquely suited for implementing feedback control of the resonator temperature, thereby stabilizing the frequency silicon micromechanical resonators and enabling their use in high-stability frequency reference applications.
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07.10.Cm Micromechanical devices and systems
84.30.Ng Oscillators, pulse generators, and function generators
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
84.30.Bv Circuit theory

Temporal characteristics of surface-acoustic-wave-driven luminescence from a lateral p-n junction

J. R. Gell, M. B. Ward, A. J. Shields, P. Atkinson, S. P. Bremner, D. Anderson, M. Kataoka, C. H. W. Barnes, G. A. C. Jones, and D. A. Ritchie

Appl. Phys. Lett. 91, 013506 (2007); http://dx.doi.org/10.1063/1.2753759 (3 pages) | Cited 3 times

Online Publication Date: 3 July 2007

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Short radio frequency pulses were used to study the surface-acoustic-wave-driven light emission from a molecular beam epitaxy regrown GaAs/AlGaAs lateral p-n junction. The luminescence provides a fast probe of the signals arriving at the junction allowing the authors to temporally separate the effect of the surface-acoustic-wave from pickup of the free space electromagnetic wave. Oscillations in the light intensity are resolved at the resonant frequency of the transducer, suggesting that the surface-acoustic-wave is transporting electrons across the junction in packets.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
68.35.Iv Acoustical properties

Efficient blue and white organic light-emitting devices based on a single bipolar emitter

Silu Tao, Chun Sing Lee, Shuit-Tong Lee, and Xiaohong Zhang

Appl. Phys. Lett. 91, 013507 (2007); http://dx.doi.org/10.1063/1.2742289 (3 pages) | Cited 25 times

Online Publication Date: 5 July 2007

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Excellent bipolar carrier transport properties of 2,7-dipyrenyl-9,9′-dimethyl-fluorene (DPF) have been elucidated by using different device structures. A nondoped device using DPF as host emitter showed highly-efficient blue emission with a maximum efficiency of 6.0 cd/A and CIE coordinates of x = 0.15 and y = 0.19. Another device based on rubrene-doped DPF as emission layer gave pure high-efficiency white emission with good color stability, a maximum efficiency of 10.5 cd/A, and CIE coordinates of x = 0.28 and y = 0.35. The excellent bipolar transport capability and high performance as both emitter and host suggest that DPF is an efficient and versatile material for various applications in organic light-emitting devices.
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85.60.Jb Light-emitting devices

Near-infrared sensitive small molecule organic photovoltaic cells based on chloroaluminum phthalocyanine

Rhonda F. Bailey-Salzman, Barry P. Rand, and Stephen R. Forrest

Appl. Phys. Lett. 91, 013508 (2007); http://dx.doi.org/10.1063/1.2752992 (3 pages) | Cited 58 times

Online Publication Date: 5 July 2007

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The use of chloroaluminum phthalocyanine (ClAlPc) as a donor and C60 as an acceptor in planar double heterojunction organic photovoltaic cells with response extending into the near infrared is demonstrated. X-ray diffraction indicates that under the conditions used in this study ClAlPc grows as an amorphous film. Although the absorption and film morphology show no dependence on growth rate, device performance is optimized at a growth rate of 0.5 Å/s, producing cells whose best performance gives an open circuit voltage of 0.68±0.01 V, a responsivity of 0.062±0.007 A/W, a fill factor of 0.50±0.04, and a power conversion efficiency of 2.1±0.1% under simulated AM1.5G, 1 sun intensity illumination. This cell also displays low dark current under reverse bias, 2.4×10−8 A/cm2 at −1 V.
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85.60.-q Optoelectronic devices

Electrical transport properties of (CoxAl1−x)2O3−v oxide magnetic semiconductor and corresponding Co–Al2O3 granular films

Y. F. Tian, Y. P. Zhang, Shi-shen Yan, G. L. Liu, Y. X. Chen, L. M. Mei, G. Ji, and Z. Zhang

Appl. Phys. Lett. 91, 013509 (2007); http://dx.doi.org/10.1063/1.2754645 (3 pages) | Cited 3 times

Online Publication Date: 5 July 2007

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(CoxAl1−x)2O3−v oxide magnetic semiconductor films were synthesized by introducing an impurity band in the insulating Al2O3 band gap, and the corresponding granular films were obtained by annealing. For both kinds of films, their electrical transport properties are well described by spin dependent variable range hopping mechanism instead of the usually expected intergrain tunnelling. The magnetoresistance was also discussed.
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75.50.Pp Magnetic semiconductors
73.61.Le Other inorganic semiconductors
61.72.Cc Kinetics of defect formation and annealing
73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Deep-depletion physics-based analytical model for scanning capacitance microscopy carrier profile extraction

K. M. Wong and W. K. Chim

Appl. Phys. Lett. 91, 013510 (2007); http://dx.doi.org/10.1063/1.2753827 (3 pages)

Online Publication Date: 5 July 2007

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An approach for fast and accurate carrier profiling using deep-depletion analytical modeling of scanning capacitance microscopy (SCM) measurements is shown for an ultrashallow p-n junction with a junction depth of less than 30 nm and a profile steepness of about 3 nm per decade change in carrier concentration. In addition, the analytical model is also used to extract the SCM dopant profiles of three other p-n junction samples with different junction depths and profile steepnesses. The deep-depletion effect arises from rapid changes in the bias applied between the sample and probe tip during SCM measurements. The extracted carrier profile from the model agrees reasonably well with the more accurate carrier profile from inverse modeling and the dopant profile from secondary ion mass spectroscopy measurements.
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61.72.S- Impurities in crystals
61.72.up Other materials
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Electromigration of the conducting polymer in organic semiconductor devices and its stabilization by cross-linking

Rui-Qi Png, Perq-Jon Chia, Sankaran Sivaramakrishnan, Loke-Yuen Wong, Mi Zhou, Lay-Lay Chua, and Peter K-H. Ho

Appl. Phys. Lett. 91, 013511 (2007); http://dx.doi.org/10.1063/1.2749178 (3 pages) | Cited 15 times

Online Publication Date: 6 July 2007

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X-ray photoelectron spectroscopy (XPS) measurement of the ratio of poly(3,4-ethylenedioxythiophene) (PEDT) to polystyrenesulfonate (PSS) reveals accumulation of PEDT+ at the interface between the PEDT:PSSH hole-injection layer and the organic semiconductor during diode operation. This ionic drift of PEDT+ occurs even at low fields of 1 V cm−1, which will have an impact on the operational stability of the characteristics of organic light-emitting diodes. XPS and Raman spectroscopy indicate that dedoping of PEDT+ does not occur significantly in hole-only devices. Cross-linking at the 1 mol % level can stabilize the conducting polymer sufficiently against electromigration.
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85.60.Jb Light-emitting devices

Frequency response analysis of pentacene thin-film transistors with low impedance contact by interface molecular doping

Tetsuhiko Miyadera, Takeo Minari, Kazuhito Tsukagoshi, Hiromi Ito, and Yoshinobu Aoyagi

Appl. Phys. Lett. 91, 013512 (2007); http://dx.doi.org/10.1063/1.2754350 (3 pages) | Cited 20 times

Online Publication Date: 6 July 2007

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See Also: Publisher's Note

Show Abstract
Frequency response measurements were performed on top-contact pentacene organic thin-film transistors (OTFTs). The ac characteristics of OTFTs are strongly limited by the contact interface between a metallic electrode and a pentacene thin film. Local doping of a charge transfer molecule (CTM) into the contact interface efficiently improves the ac characteristics. Metal-insulator-semiconductor capacitance measurements revealed that the interface contains parasitic impedance composed of capacitance and resistance in parallel. The parasitic impedance was suppressed by CTM doping of the interface. The limitation factors for the frequency of operation in such an OTFT are discussed based on the experimental results and an equivalent circuit model.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling
85.40.Ry Impurity doping, diffusion and ion implantation technology
84.32.Tt Capacitors
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