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4 Jun 2007

Volume 90, Issue 23, Articles (23xxxx)

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Appl. Phys. Lett. 90, 233105 (2007); http://dx.doi.org/10.1063/1.2747052 (3 pages)

Youhui Gao, Daisuke Shindo, Yuping Bao, and Kannan Krishnan
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Microfiber knot dye laser based on the evanescent-wave-coupled gain

Xiaoshun Jiang, Qinghai Song, Lei Xu, Jian Fu, and Limin Tong

Appl. Phys. Lett. 90, 233501 (2007); http://dx.doi.org/10.1063/1.2746935 (3 pages) | Cited 33 times

Online Publication Date: 4 June 2007

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The authors demonstrate a composite microring laser formed by immersing a silica microfiber knot in a rhodamine 6G dye solution. When the dye molecules are evanescently pumped by 532 nm wavelength laser pulses guided along a 350 μm diameter knot, lasing oscillation occurs inside the evanescently coupled closed-ring microcavity with a linewidth of about 0.06 nm. Laser emission around 570 and 580 nm wavelengths, which is evanescently coupled back into the microfiber, is observed with a threshold of about 9.2 μJ/pulse. The use of the microfiber knot cavity suggests a convenient and efficient approach to both pumping and collection of the evanescent-wave-coupled dye laser.
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42.55.Wd Fiber lasers
42.55.Mv Dye lasers
42.55.Sa Microcavity and microdisk lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.By Design of specific laser systems

Flexural and torsional vibration modes in low temperature thin-film silicon paddle microresonators

T. Adrega, V. Chu, and J. P. Conde

Appl. Phys. Lett. 90, 233502 (2007); http://dx.doi.org/10.1063/1.2745644 (3 pages)

Online Publication Date: 4 June 2007

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Electrostatically actuated paddle microresonators based on hydrogenated amorphous silicon were fabricated on glass substrates. The use of amorphous silicon as the structural material of a microelectromechanical device allows processing temperatures below 110 °C, offering the possibility of using large-area, low cost, and even flexible substrates. The microdevice geometry allows the excitation of flexural and torsional oscillations. Oscillation modes are distinguishable through the dependence of their resonance frequency on the length of the resonator’s paddle. Here the authors show resonance frequencies in the megahertz range and quality factors around 103. Parametric amplification was also observed with resonance peaks having quality factors reaching 104.
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42.82.Gw Other integrated-optical elements and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.65.Yj Optical parametric oscillators and amplifiers

Photoactivated and patternable charge transport materials and their use in organic light-emitting devices

Jie Liu, Larry N. Lewis, and Anil R. Duggal

Appl. Phys. Lett. 90, 233503 (2007); http://dx.doi.org/10.1063/1.2746404 (3 pages)

Online Publication Date: 5 June 2007

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Organic light-emitting devices (OLEDs) usually employ at least one organic semiconductor layer that acts as a hole-injection material. The prototypical example is a conjugated polymer such as poly(3,4-ethylenedioxythiophene) heavily p doped with polystyrene sulfonic acid. Here, the authors describe a chemical doping strategy for hole injection material formulation that enables spatial patterning of the material conductivity through optical activation. The strategy utilizes an organic photoacid generator (PAG) dispersed in a polymeric organic semiconductor host. Upon UV irradiation, the PAG decomposes and generates a strong protonic acid that subsequently p dopes the host. The authors demonstrate an OLED made with such a light-activated hole-injection material and show that arbitrary emission patterning can be accomplished. This approach may provide a simple, low cost path toward specialty lighting and signage applications for OLED technology.
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61.72.up Other materials
72.80.Le Polymers; organic compounds (including organic semiconductors)
72.20.-i Conductivity phenomena in semiconductors and insulators
85.40.Hp Lithography, masks and pattern transfer

High power and high efficiency blue light emitting diode on freestanding semipolar (10mathmath) bulk GaN substrate

Hong Zhong, Anurag Tyagi, Natalie N. Fellows, Feng Wu, Roy B. Chung, Makoto Saito, Kenji Fujito, James S. Speck, Steven P. DenBaars, and Shuji Nakamura

Appl. Phys. Lett. 90, 233504 (2007); http://dx.doi.org/10.1063/1.2746418 (3 pages) | Cited 41 times

Online Publication Date: 5 June 2007

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Blue InGaN/GaN multiple-quantum-well light emitting diodes with a peak emission wavelength of 444 nm were grown on low extended defect density semipolar (10mathmath) bulk GaN substrates by conventional metal-organic chemical vapor deposition. The calculated external quantum efficiency and output power at a drive current of 20 mA under pulsed operations (10% duty cycle) were 29% and 16.21 mW, respectively. The device exhibited virtually no peak electroluminescence wavelength shift with increasing drive currents, indicating a significant reduction of polarization-related internal electric fields.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.40.Sz Deposition technology

Anomalous negative bias temperature instability behavior in p-channel metal-oxide-semiconductor field-effect transistors with HfSiON/SiO2 gate stack

Shih-Chang Chen, Chao-Hsin Chien, and Jen-Chung Lou

Appl. Phys. Lett. 90, 233505 (2007); http://dx.doi.org/10.1063/1.2745649 (3 pages)

Online Publication Date: 5 June 2007

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In this letter, the authors systematically investigated the behavior of negative bias temperature instability of p-channel metal-oxide-semiconductor field-effect transistors with HfSiON/SiO2 gate stack. They found that typical linear extrapolation does not work well for the lifetime extraction at the normal operation conditions since the polarities of the net trapped charge inside the high-κ dielectrics are not the same at lower and higher stress voltage regimes. In other words, as ∣Vg∣<2.5 V electron trapping dominated while hole trapping dominated when ∣Vg∣>2.5 V. This phenomenon obviously contradicts the essence of the linear prediction in which the same degradation mechanism is assumed through the entire stress voltage range.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Long range diffusion noise in platinum microwires with metallic adhesion layers

Z. Moktadir, J. W. van Honschoten, and M. Elwenspoek

Appl. Phys. Lett. 90, 233506 (2007); http://dx.doi.org/10.1063/1.2746961 (3 pages) | Cited 1 time

Online Publication Date: 6 June 2007

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Voltage fluctuations of platinum wires hosted by silicon nitride beams were investigated. The authors considered four variants of the wires: three with an adhesion layer and one without an adhesion layer. They found that the presence of an adhesion layer changes the nature of the power spectrum which is 1/f for wires with no adhesion layers and 1/f3/2 for wires with an adhesion layer. They attribute the value of the exponent α = 3/2 found in wires with adhesion layers to the long range diffusion of oxygen atoms along the interface between the adhesion layer and the platinum layer.
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66.30.H- Self-diffusion and ionic conduction in nonmetals
68.35.Np Adhesion
72.70.+m Noise processes and phenomena

Dielectric charging in radio frequency microelectromechanical system capacitive switches: A study of material properties and device performance

G. Papaioannou, J. Papapolymerou, P. Pons, and R. Plana

Appl. Phys. Lett. 90, 233507 (2007); http://dx.doi.org/10.1063/1.2746056 (3 pages) | Cited 13 times

Online Publication Date: 6 June 2007

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The paper analyze the direct relation between the dielectric polarization mechanisms and the radio frequency microelectromechanical system capacitive switches performance. The dielectric polarization mechanisms are investigated in metal-insulator-metal capacitors with the aid of the thermally stimulated depolarization current method. The performance of microelectromechanical system is studied through the temperature dependence of the bias for the minimum capacitance. The simultaneous assessment allows the discrimination of dipolar and space charge polarization that allows the prediction of the shift of capacitance minimum with temperature.
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84.32.Dd Connectors, relays, and switches
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
84.32.Tt Capacitors

Effects of the surface roughness of plastic-compatible inorganic dielectrics on polymeric thin film transistors

Michael L. Chabinyc, Rene Lujan, Fred Endicott, Michael F. Toney, Iain McCulloch, and Martin Heeney

Appl. Phys. Lett. 90, 233508 (2007); http://dx.doi.org/10.1063/1.2746955 (3 pages) | Cited 22 times

Online Publication Date: 6 June 2007

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The effects of the roughness of the gate dielectric on the performance of thin film transistors (TFTs) fabricated with poly(2,5-bis(3-hexadecylthiophen-2-yl)thieno[3,2-b] thiophene) (PBTTT-C16) were examined. The field effect mobility of coplanar TFTs made with PBTTT-C16 and plasma-enhanced chemical vapor deposited SiO2/SiNx dielectrics decreased nearly exponentially with surface roughness. Films of PBTTT-C16 have similar crystalline structure on smooth and rough surfaces, but the domain size decreases with increasing roughness. Surface roughness was found to have less of an impact on field effect mobility than the chemical treatment of the dielectric.
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85.30.Tv Field effect devices
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Direct printing of organic transistors with 2 μm channel resolution

Hee Hyun Lee, J. J. Brondjik, N. G. Tassi, S. Mohapatra, M. Grigas, P. Jenkins, K. J. Dimmler, and Graciela B. Blanchet

Appl. Phys. Lett. 90, 233509 (2007); http://dx.doi.org/10.1063/1.2746072 (3 pages) | Cited 6 times

Online Publication Date: 7 June 2007

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Organic materials offer the possibility of printing flexible electronic devices with large area coverage in a printing press. Usually this vision conflicts with the requirement of high-resolution feature formation. The authors demonstrate here that thin film transistors with 2 μm channel length can be printed using a reel-to-reel compatible process. The development of a dry printing method used in combination with a high-resolution, solvent resistant plates, and sintered metallic nanoinks enables high-resolution printing of functional liquid inks. In addition, dry printing allows for the sequential printing of solid films overcoming the severe solvent incompatibility issues faced by standard printing techniques.
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85.30.Tv Field effect devices

Emitter degradation in quantum dot intermediate band solar cells

A. Martí, N. López, E. Antolín, E. Cánovas, A. Luque, C. R. Stanley, C. D. Farmer, and P. Díaz

Appl. Phys. Lett. 90, 233510 (2007); http://dx.doi.org/10.1063/1.2747195 (3 pages) | Cited 47 times

Online Publication Date: 7 June 2007

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The characteristics of intermediate band solar cells containing 10, 20, and 50 InAs quantum dot (QD) layers embedded in otherwise “standard” (Al,Ga)As solar cell structures have been compared. The short-circuit current densities of the cells decreased and the quantum efficiencies of the devices showed a concomitant reduction in the minority carrier lifetime in the p emitters with increasing number of QD layers. Dislocations threading up from the QDs toward the surface of the cells, and revealed by bright field scanning transmission electron microscopy, are the most likely cause of the deterioration in the electrical performance of the cells.
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84.60.Jt Photoelectric conversion

Effect of donor-complex-defect-induced dipole field on InAs/GaAs quantum dot infrared photodetector activation energy

Z. Y. Zhao, C. Yi, K. R. Lantz, and A. D. Stiff-Roberts

Appl. Phys. Lett. 90, 233511 (2007); http://dx.doi.org/10.1063/1.2747199 (3 pages) | Cited 7 times

Online Publication Date: 7 June 2007

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In order to understand dopant incorporation in quantum dot infrared photodetectors, three quantum dot (QD) Schottky diodes (undoped, delta doped, and modulation doped) have been investigated. Donor-complex-defect (DX) centers have been observed by photocapacitance quenching in the doped diodes only. When the applied bias increases, the doped samples show a rapid increase in dark current and a resulting dramatic decrease in QD activation energy. The activation energy reduction could be related to a dipole field between positively charged DX centers and electrons in QDs. A transport mechanism is proposed to explain the observed activation energy bias dependence in the doped samples.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.30.Kk Junction diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.40.Ry Impurity doping, diffusion and ion implantation technology

Energy-recycling pixel for active-matrix organic light-emitting diode display

Che-Yu Yang, Ting-Yi Cho, Yen-Yu Chen, Chih-Jen Yang, Chao-Yu Meng, Chieh-Hung Yang, Po-Chuan Yang, Hsu-Yu Chang, Chun-Yuan Hsueh, Chung-Chih Wu, and Si-Chen Lee

Appl. Phys. Lett. 90, 233512 (2007); http://dx.doi.org/10.1063/1.2746960 (3 pages) | Cited 12 times

Online Publication Date: 11 June 2007

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The authors report a pixel structure for active-matrix organic light-emitting diode (OLED) displays that has a hydrogenated amorphous silicon solar cell inserted between the driving polycrystalline Si thin-film transistor and the pixel OLED. Such an active-matrix OLED pixel structure not only exhibits a reduced reflection (and thus improved contrast) compared to conventional OLEDs but also is capable of recycling both incident photon energies and internally generated OLED radiation. Such a feature of energy recycling may be of use for portable/mobile electronics, which are particularly power aware.
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42.79.Kr Display devices, liquid-crystal devices
85.60.Jb Light-emitting devices
84.60.Jt Photoelectric conversion
85.30.Tv Field effect devices

Near bulk-limited R0A of long-wavelength infrared type-II InAs/GaSb superlattice photodiodes with polyimide surface passivation

Andrew Hood, Pierre-Yves Delaunay, Darin Hoffman, Binh-Minh Nguyen, Yajun Wei, Manijeh Razeghi, and Vaidya Nathan

Appl. Phys. Lett. 90, 233513 (2007); http://dx.doi.org/10.1063/1.2747172 (3 pages) | Cited 37 times

Online Publication Date: 11 June 2007

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Effective surface passivation of type-II InAs/GaSb superlattice photodiodes with cutoff wavelengths in the long-wavelength infrared is presented. A stable passivation layer, the electrical properties of which do not change as a function of the ambient environment nor time, has been prepared by a solvent-based surface preparation, vacuum desorption, and the application of an insulating polyimide layer. Passivated photodiodes, with dimensions ranging from 400×400 to 25×25 μm2, with a cutoff wavelength of ∼ 11 μm, exhibited near bulk-limited R0A values of ∼ 12 Ω cm2, surface resistivities in excess of 104 Ω cm, and very uniform current-voltage behavior at 77 K.
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85.60.Dw Photodiodes; phototransistors; photoresistors
81.65.Rv Passivation
79.70.+q Field emission, ionization, evaporation, and desorption

Oxide-apertured microcavity single-photon emitting diode

D. J. P. Ellis, A. J. Bennett, A. J. Shields, P. Atkinson, and D. A. Ritchie

Appl. Phys. Lett. 90, 233514 (2007); http://dx.doi.org/10.1063/1.2747200 (3 pages) | Cited 10 times

Online Publication Date: 11 June 2007

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The authors have developed a microcavity single-photon source based on a single quantum dot within a planar cavity in which wet oxidation of a high-aluminium content layer provides lateral confinement of both the photonic mode and the injection current. Lateral confinement of the optical mode in optically pumped structures produces a strong enhancement of the radiative decay rate. Using microcavity structures with doped contact layers, they demonstrate a single-photon emitting diode where current may be injected into a single dot.
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85.60.Dw Photodiodes; phototransistors; photoresistors
81.65.Mq Oxidation
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