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6 Feb 2006

Volume 88, Issue 6, Articles (06xxxx)

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Appl. Phys. Lett. 88, 063509 (2006); http://dx.doi.org/10.1063/1.2171834 (3 pages)

M. Feng, N. Holonyak, R. Chan, A. James, and G. Walter
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Evidence of water-related discrete trap state formation in pentacene single-crystal field-effect transistors

C. Goldmann, D. J. Gundlach, and B. Batlogg

Appl. Phys. Lett. 88, 063501 (2006); http://dx.doi.org/10.1063/1.2171479 (3 pages) | Cited 38 times

Online Publication Date: 6 February 2006

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We report on the generation of a discrete trap state during negative gate bias stress in pentacene single-crystal “flip-crystal” field-effect transistors with a SiO2 gate dielectric. Trap densities of up to 2∙1012 cm−2 were created in the experiments. Trap formation and trap relaxation are distinctly different above and below ∼ 280 K. In devices in which a self-assembled monolayer on top of the SiO2 provides a hydrophobic insulator surface we do not observe trap formation. These results indicate the microscopic cause of the trap state to be related to molecular layers of water adsorbed on the SiO2 surface.
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85.30.Tv Field effect devices

Effect of degassed elements on the degradation behavior of carbon nanotube cathodes in sealed field emission-backlight units

Sora Lee and Duk Young Jeon

Appl. Phys. Lett. 88, 063502 (2006); http://dx.doi.org/10.1063/1.2167791 (3 pages) | Cited 13 times

Online Publication Date: 6 February 2006

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The effect of degassed elements from the phosphor layer on a carbon nanotube (CNT) cathode was investigated. During the operation of field emission backlight units, it was found that zinc and sulfur were degassed from the phosphor anode. X-ray photoelectron spectroscopy analysis showed that sp2 bonding in the CNTs changed to zinc-assisted sp3-like bonding, modified by the adsorption of the zinc. The change of the CNT structure to a nonhexagonal carbon network suggests that the electron emission from the degraded CNT tips decreases due to the higher work function of sp3-like bonding, compared to that of sp2 bonding.
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85.45.Fd Field emission displays (FEDs)
85.35.Kt Nanotube devices
79.70.+q Field emission, ionization, evaporation, and desorption

Shapiro steps observed in annular intrinsic Josephson junctions at low microwave frequencies

H. B. Wang, S. M. Kim, S. Urayama, M. Nagao, T. Hatano, S. Arisawa, T. Yamashita, and P. H. Wu

Appl. Phys. Lett. 88, 063503 (2006); http://dx.doi.org/10.1063/1.2172010 (3 pages) | Cited 3 times

Online Publication Date: 7 February 2006

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With annular intrinsic Josephson junctions structured from a slice of Bi2Sr2CaCu2O8+δ single crystal 200 nm thick, we have devised a way to inject fluxons into the junctions only by sweeping the bias current. The stacks have shown typical properties concerning Josephson fluxon conservation. These annular junctions are sensitive to microwave irradiation, and quite sharp Shapiro steps have been observed at ∼ 20 GHz which is much lower than the plasma frequency of the junctions, indicating many applications can be possible with practically accessible microwave sources.
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74.72.-h Cuprate superconductors
74.50.+r Tunneling phenomena; Josephson effects
74.25.N- Response to electromagnetic fields

Spiral springs and microspiral springs for chemical and biological sensing

Hai-Feng Ji, Yanqing Lu, Hongwei Du, Xiaohe Xu, and Thomas Thundat

Appl. Phys. Lett. 88, 063504 (2006); http://dx.doi.org/10.1063/1.2172407 (3 pages) | Cited 1 time

Online Publication Date: 7 February 2006

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This work demonstrates that a mechanical device based on spiral spring or microspiral spring has a broad range of applications for detection of chemical and biological species. The surface stress changes or polymer volume changes on one side of the spiral spring extend or contract a spiral spring. The macrosize spiral spring can be used for power-free sensor development.
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87.80.-y Biophysical techniques (research methods)
82.80.-d Chemical analysis and related physical methods of analysis

Fast-response no-bias-bend liquid crystal displays using nanostructured surfaces

Fion Sze-Yan Yeung and Hoi-Sing Kwok

Appl. Phys. Lett. 88, 063505 (2006); http://dx.doi.org/10.1063/1.2172732 (3 pages) | Cited 50 times

Online Publication Date: 7 February 2006

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We present results of a fast-response no-bias-bend (NBB) liquid crystal display, made possible by using a nanostructured alignment layer. Such alignment layers allow high pretilt angles of over 45° to be fabricated reliably. Thus, a stable bend configuration pi-cell can be achieved without applying any bias voltage to the cell. This NBB cell has a total on-off response time of less than 1.8 ms and is faster than the corresponding optically compensated bend cell with a low pretilt angle.
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42.79.Kr Display devices, liquid-crystal devices
85.60.Pg Display systems

Leakage suppression by asymmetric area electrodes in metal-semiconductor-metal photodetectors

Ali K. Okyay, Chi On Chui, and Krishna C. Saraswat

Appl. Phys. Lett. 88, 063506 (2006); http://dx.doi.org/10.1063/1.2171648 (2 pages) | Cited 4 times

Online Publication Date: 7 February 2006

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We have studied the effect of varying electrode area asymmetry on the leakage behavior of metal-semiconductor-metal photodetectors (MSM-PDs). We demonstrate, an effective suppression of dark current (Idark) with the application of asymmetric electrode area and appropriate biasing scheme in MSM-PDs. More than 2× reduction in Idark is obtained in photodetectors fabricated on silicon. Photoresponse of these detectors have also been monitored and normalized photo-to-dark current ratio (NPDR) metric is utilized for objective assessment of detector performance. Significant enhancement in NPDR is shown to be accomplished with the asymmetric Si MSM-PDs.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Organic field effect transistor mobility from transient response analysis

Lawrence Dunn, Debarshi Basu, Liang Wang, and Ananth Dodabalapur

Appl. Phys. Lett. 88, 063507 (2006); http://dx.doi.org/10.1063/1.2172023 (3 pages) | Cited 24 times

Online Publication Date: 8 February 2006

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An electronic method for analyzing the transient response of a pentacene organic field effect transistor at time scales below 100 ns is presented with analysis that allows extraction of estimated field-dependent device mobility from the measured carrier velocity. A second technique we propose is the use of T-SPICE simulations of transient response data of the device behavior between ∼ 100 ns and ∼ 3 μs. These results are compared with lower field-effect mobilities extracted from the transient data at 250 μs and the dc drain current (Id) versus source-drain voltage (Vds) characteristics in the saturation regime. This trend of decreasing mobility with increasing time is perhaps due to the absence of the bias stress effect at small time scales.
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85.30.Tv Field effect devices

Phosphorescence of red Os(fptz)2(PPh2Me)2 doped organic light-emitting devices with n and p hosts

Tswen-Hsin Liu, Shih-Feng Hsu, Meng-Hung Ho, Chi-Hung Liao, Yao-Shan Wu, Chin H. Chen, Yung-Liang Tung, Pei-Chi Wu, and Yun Chi

Appl. Phys. Lett. 88, 063508 (2006); http://dx.doi.org/10.1063/1.2172405 (3 pages) | Cited 7 times

Online Publication Date: 8 February 2006

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We have applied a stericly-hindered red phosphorescent dopant Os(fptz)2(PPh2Me)2 [fptz = 3-trifluoromethyl-5-(2-pyridyl)-1,2,4-triazole, PPh2Me = phosphine ligand] in p-type 4,4′-N,N′-dicarbazole-biphenyl or n-type bis(2-methyl-8-quinolinolato)(p-phenylphenolato) aluminum host and found that the latter produced higher luminance efficiency at lower doping concentration. We present a model to rationalize this phenomenon in which the n-type host impedes hole transport, which leads to narrower recombination zone near the hole transport layer/emission layer interface than the p-type host, hence, more effective recombination.
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85.60.Jb Light-emitting devices
61.72.up Other materials
78.55.-m Photoluminescence, properties and materials
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Signal mixing in a multiple input transistor laser near threshold

M. Feng, N. Holonyak, R. Chan, A. James, and G. Walter

Appl. Phys. Lett. 88, 063509 (2006); http://dx.doi.org/10.1063/1.2171834 (3 pages) | Cited 12 times

Online Publication Date: 8 February 2006

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A single-emitter multiple-input transistor laser has been realized and demonstrated in signal mixing, yielding in the stimulated-recombination region near laser threshold frequency conversion with simultaneously an electrical and optical output signal. In the unique nonlinear region of compression of the transistor I-V characteristics (β ≡ ΔIC/ΔIB, βspon>βstim), input signals f1 = 2 GHz and f2 = 2.1 GHz are converted into mf1±nf2 ranging from 0.1 to 8.4 GHz. Stimulated emission (enhanced recombination) changes the transistor into a special form of nonlinear element, a special form of electronic processor or “switch.”
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Improvement in electron holographic phase images of focused-ion-beam-milled GaAs and Si p-n junctions by in situ annealing

David Cooper, Alison C. Twitchett, Philippa K. Somodi, Paul A. Midgley, Rafal E. Dunin-Borkowski, Ian Farrer, and David A. Ritchie

Appl. Phys. Lett. 88, 063510 (2006); http://dx.doi.org/10.1063/1.2172068 (3 pages) | Cited 27 times

Online Publication Date: 8 February 2006

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Low temperature (200–600 °C) annealing in the transmission electron microscope (TEM) is used to provide a significant noise reduction in phase images of focused-ion-beam-milled GaAs and Si p-n junctions recorded using off-axis electron holography, as well as increasing the measured phase shifts across the junctions. Our results suggest that annealing removes defects resulting from Ga+ implantation and reactivates dopant atoms in the thin TEM specimens. In GaAs, electrically inactive surface layer thicknesses are reduced from 80 to 17 nm on each specimen surface after annealing at 500 °C. In Si the improvement is from 25 to 5 nm.
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42.40.-i Holography
61.72.Cc Kinetics of defect formation and annealing
61.72.S- Impurities in crystals

Channel-width dependence of low-frequency noise in process tensile-strained n-channel metal-oxide-semiconductor transistors

Ming-Pei Lu, Wen-Chin Lee, and Ming-Jer Chen

Appl. Phys. Lett. 88, 063511 (2006); http://dx.doi.org/10.1063/1.2172287 (3 pages) | Cited 7 times

Online Publication Date: 8 February 2006

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Low-frequency noise measurement in process tensile-strained n-channel metal-oxide-semiconductor field-effect transistors yields the density of the interface states, exhibiting a decreasing trend while decreasing the channel width. This finding corroborates the group of Pb centers caused by the lattice mismatch at (100) Si-SiO2 interface as the origin of the underlying interface states. The inverse narrow width effect appears to be insignificant, substantially confirming the validity of the noise measurement. The present noise experiment therefore points to the enhancement of the tensile strain in the presence of channel narrowing, which in turn reduces the lattice mismatch.
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85.30.Tv Field effect devices

Hole-mobility limit of amorphous silicon solar cells

Jianjun Liang, E. A. Schiff, S. Guha, Baojie Yan, and J. Yang

Appl. Phys. Lett. 88, 063512 (2006); http://dx.doi.org/10.1063/1.2170405 (3 pages) | Cited 10 times

Online Publication Date: 10 February 2006

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We present temperature-dependent measurements and modeling for a thickness series of hydrogenated amorphous silicon nip solar cells. The comparison indicates that the maximum power density (PMAX) from the as-deposited cells has achieved the hole-mobility limit established by valence bandtail trapping, and PMAX is thus not significantly limited by intrinsic-layer dangling bonds or by the doped layers and interfaces. Measurements of the temperature-dependent properties of light-soaked cells show that the properties of as-deposited and light-soaked cells converge below 250 K; a model perturbing the valence band tail traps with a density of dangling bonds accounts adequately for the convergence effect.
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84.60.Jt Photoelectric conversion
72.20.Fr Low-field transport and mobility; piezoresistance
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
71.55.Cn Elemental semiconductors
72.80.Cw Elemental semiconductors

Micron-scale organic thin film transistors with conducting polymer electrodes patterned by polymer inking and stamping

Dawen Li and L Jay Guo

Appl. Phys. Lett. 88, 063513 (2006); http://dx.doi.org/10.1063/1.2168669 (3 pages) | Cited 36 times

Online Publication Date: 10 February 2006

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We report organic thin film transistors (OTFTs) with conductive polymer poly (3,4-ethylenedioxythiophene)/poly(4-styrenesulphonate) (PEDOT) electrodes that are fabricated by a simple polymer inking and stamping technique. An OTFT channel length of 2 μm has been achieved. This patterning technique is a purely additive process, which does not affect the functionality of the conductive polymers, and is fully compatible for patterning on a flexible substrate. Electrical characteristics of top contact (TC) pentacene TFTs with PEDOT electrodes is superior to those with gold electrodes due to a lower carrier injection barrier. Extracted contact resistance shows that the channel length of TC OTFTs can be further reduced to increase the drain current.
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85.30.Tv Field effect devices
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