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25 Oct 2004

Volume 85, Issue 17, pp. 3657-3939

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 3851 (2004); http://dx.doi.org/10.1063/1.1808886 (3 pages)

P. Guha, S. Kar, and S. Chaudhuri
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Current transport mechanism in InGaP∕GaAsSb∕GaAs double-heterojunction bipolar transistors

B. P. Yan, C. C. Hsu, X. Q. Wang, and E. S. Yang

Appl. Phys. Lett. 85, 3884 (2004); http://dx.doi.org/10.1063/1.1808891 (3 pages)

Online Publication Date: 29 October 2004

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We have developed InGaP∕GaAsSb∕GaAs double-heterojunction bipolar transistors (DHBTs) with low turn-on voltage and high current gain by using a narrow energy bandgap GaAsSb layer as the base and an InGaP layer as the emitter. The current transport mechanism is examined by measuring both of the terminal currents in forward and reverse mode. The results show that the dominant current transport mechanism in the InGaP∕GaAsSb∕GaAs DHBTs is the transport of carriers across the base layer. This finding suggests that the bandgap offset produced by incorporating Sb composition into GaAs mainly appears on the valence band and the conduction-band offset in InGaP∕GaAsSb heterojunction is very small.
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85.30.Pq Bipolar transistors
73.21.Ac Multilayers

Current modulation of a hygroscopic insulator organic field-effect transistor

T. G. Bäcklund, H. G. O. Sandberg, R. Österbacka, and H. Stubb

Appl. Phys. Lett. 85, 3887 (2004); http://dx.doi.org/10.1063/1.1811798 (3 pages) | Cited 20 times

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We have fabricated solution processable polymer transistors with high conductivity, requiring only a few volts for obtaining good current modulation. The devices can be fabricated and operated in air and the operation is greatly enhanced in humid atmosphere. Devices reach an On∕Off ratio of about 600 and a subthreshold swing of 500 mV per decade operating on voltages less than 2 V. In this letter the mechanism behind the current modulation is investigated, and we show that the current is modulated through ion-assisted oxidation and reduction of the semiconductor by ions moving vertically in the insulator material to the transistor channel.
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85.30.Tv Field effect devices
72.60.+g Mixed conductivity and conductivity transitions
73.61.Ph Polymers; organic compounds

High ambipolar and balanced carrier mobility in regioregular poly(3-hexylthiophene)

S. A. Choulis, Y. Kim, J. Nelson, D. D. C. Bradley, M. Giles, M. Shkunov, and I. McCulloch

Appl. Phys. Lett. 85, 3890 (2004); http://dx.doi.org/10.1063/1.1805175 (3 pages) | Cited 79 times

Online Publication Date: 29 October 2004

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The carrier transport of carefully purified regioregular poly(3-hexylthiophene) films has been studied using time-of-flight photocurrent measurements. We find balanced ambipolar transport with a room-temperature mobility for holes of 3×10−4 cm2 V−1 s−1 and for electrons of 1.5×10−4 cm2 V−1 s−1 at electric fields ⩾105 V∕cm. The transport is relatively field independent and weakly temperature dependent, pointing to a high degree of chemical regioregularity and purity. These factors make poly(3-hexylthiophene) attractive for use in a range of electronic applications.
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73.61.Ph Polymers; organic compounds
73.50.Pz Photoconduction and photovoltaic effects
73.50.Dn Low-field transport and mobility; piezoresistance

Proximity effect of electron beam lithography for single-electron transistor fabrication

Shu-Fen Hu, Chin-Lung Sung, Kuo-Dong Huang, and Yue-Min Wan

Appl. Phys. Lett. 85, 3893 (2004); http://dx.doi.org/10.1063/1.1811803 (3 pages) | Cited 1 time

Online Publication Date: 29 October 2004

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In this letter, we shall describe a method, utilizing the proximity effect in electron beam lithography, suitable for fabricating silicon dots and devices, and demonstrate the electronic characteristics of the Si single-electron transistor. The drain current (Id) of the device oscillates against gate voltage. The electrical characteristics of the single-electron transistor were observed to be consistent with the expected behavior of electron transport through gated quantum dots, at up to 150 K. The dependence of the electrical characteristics on the dot size reveals that the Id oscillation follows from the Coulomb blockade by poly-Si grains in the poly-Si dot. The method of fabrication of this device is completely compatible with complementary metal–oxide–semiconductor technology, raising the possibility of manufacturing large-scale integrated nanoelectronic systems.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.40.Hp Lithography, masks and pattern transfer
85.35.Gv Single electron devices
73.63.Kv Quantum dots
73.23.Hk Coulomb blockade; single-electron tunneling

Improving the sensitivity of frequency modulation spectroscopy using nanomechanical cantilevers

B. M. Chernobrod, G. P. Berman, and P. W. Milonni

Appl. Phys. Lett. 85, 3896 (2004); http://dx.doi.org/10.1063/1.1809275 (3 pages) | Cited 5 times

Online Publication Date: 29 October 2004

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It is suggested that nanomechanical cantilevers can be employed as high-Q filters to circumvent laser noise limitations on the sensitivity of frequency modulation spectroscopy. In this approach, a cantilever is actuated by the radiation pressure of the amplitude modulated light that emerges from an absorber. Numerical estimates indicate that laser intensity noise will not prevent a cantilever from operating in the thermal noise limit, where the high Q’s of cantilevers are most advantageous.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.60.Fc Modulation, tuning, and mode locking
42.60.Mi Dynamical laser instabilities; noisy laser behavior
07.60.Rd Visible and ultraviolet spectrometers
42.62.Fi Laser spectroscopy
37.10.Vz Mechanical effects of light on atoms, molecules, and ions

Influence of the gate dielectric on the mobility of rubrene single-crystal field-effect transistors

A. F. Stassen, R. W. I. de Boer, N. N. Iosad, and A. F. Morpurgo

Appl. Phys. Lett. 85, 3899 (2004); http://dx.doi.org/10.1063/1.1812368 (3 pages) | Cited 111 times

Online Publication Date: 29 October 2004

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We have performed a comparative study of rubrene single-crystal field-effect transistors fabricated using different materials as gate insulator. For all materials, highly reproducible device characteristics are obtained. The achieved reproducibility permits one to observe that the mobility of the charge carriers systematically decreases with increasing the dielectric constant of the gate insulator, the decrease being proportional to ε−1. This finding demonstrates that the mobility of carriers in organic single-crystal field-effect transistors is an intrinsic property of the crystal/dielectric interface and that it does not only depend on the specific molecule used.
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85.30.Tv Field effect devices

Pentacene field-effect transistors on plastic films operating at high temperature above 100 °C

Tsuyoshi Sekitani, Shingo Iba, Yusaku Kato, and Takao Someya

Appl. Phys. Lett. 85, 3902 (2004); http://dx.doi.org/10.1063/1.1812374 (3 pages) | Cited 17 times

Online Publication Date: 29 October 2004

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We have manufactured pentacene field-effect transistors (FETs) on polyimide base films with polyimide gate dielectric layers, and characterized electronic performance and surface morphology with application of heat in the temperature range from 30 to 210 °C. It is found that mobility of pentacene FETs is enhanced from 0.27 to 0.71 cm2∕V s when measurement temperatures varies from 30 to 160 °C under light-shielding nitrogen environment. To investigate postannealing effects, we have measured transfer curves at 30 °C after many heat cycles at various temperatures. Mobility is almost constant even after annealing at 130 °C, showing the excellent stability of the present device at high temperatures.
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85.30.Tv Field effect devices
73.61.Ph Polymers; organic compounds
68.35.B- Structure of clean surfaces (and surface reconstruction)
73.50.Dn Low-field transport and mobility; piezoresistance
61.72.Cc Kinetics of defect formation and annealing

Imaging the degradation of polymer light-emitting devices

Justin Dane and Jun Gao

Appl. Phys. Lett. 85, 3905 (2004); http://dx.doi.org/10.1063/1.1810213 (3 pages) | Cited 18 times

Online Publication Date: 29 October 2004

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Anode-to-cathode spatially resolved study of polymer light-emitting device degradation has been performed based on a massive planar device structure. The unique device configuration of the extremely large planar frozen-junction light-emitting electrochemical cell allows for the study of device degradation by direct imaging. Constant current stress for an extended period results in a very unusual net luminance increase as opposed to luminance decay. Imaging of the emission zone has shown changes that are consistent with polymer degradation by the loss of electron mobility.
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85.60.Jb Light-emitting devices
73.61.Ph Polymers; organic compounds
78.66.Qn Polymers; organic compounds
78.60.-b Other luminescence and radiative recombination
73.50.Dn Low-field transport and mobility; piezoresistance

Efficiency and harmonic enhancement trends in GaN-based Gunn diodes: Ensemble Monte Carlo analysis

C. Sevik and C. Bulutay

Appl. Phys. Lett. 85, 3908 (2004); http://dx.doi.org/10.1063/1.1812376 (3 pages) | Cited 7 times

Online Publication Date: 29 October 2004

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Gallium nitride can offer a high-power alternative for millimeter-wave Gunn oscillators. Hence, an ensemble Monte Carlo-based comprehensive theoretical assessment of efficiency and harmonic enhancement in n-type GaN Gunn diodes is undertaken. First, the effects of doping notch/mesa and its position within the active channel are investigated which favors a doping notch positioned next to cathode. It is then observed that the width of the notch can be optimized to enhance the higher-harmonic operation without degrading its performance at the fundamental mode. Next, the effects of dc bias and channel doping density are investigated. Both of these have more significant effects on the higher-harmonic efficiency than the fundamental one. The lattice temperature is observed to have almost no influence up to room temperature but severely degrades the performance above room temperature. As a general behavior, the variations of temperature, channel doping, and the notch width primarily affect the phase angle between the current and voltage wave forms rather than the amplitude of oscillations. Finally, the physical origin of these Gunn oscillations is sought which clearly indicates that the intervalley scattering mechanism is responsible rather than the Γ valley nonparabolicity or the effective mass discrepancy between the Γ and the lowest satellite valleys.
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85.30.Fg Bulk semiconductor and conductivity oscillation devices (including Hall effect devices, space-charge-limited devices, and Gunn effect devices)

High-efficiency and low-voltage p‐i‐n electrophosphorescent organic light-emitting diodes with double-emission layers

Gufeng He, Martin Pfeiffer, Karl Leo, Michael Hofmann, Jan Birnstock, Robert Pudzich, and Josef Salbeck

Appl. Phys. Lett. 85, 3911 (2004); http://dx.doi.org/10.1063/1.1812378 (3 pages) | Cited 280 times

Online Publication Date: 29 October 2004

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We demonstrate high-efficiency organic light-emitting diodes by incorporating a double-emission layer (D-EML) into p‐i‐n-type cell architecture. The D-EML is comprised of two layers with ambipolar transport characteristics, both doped with the green phosphorescent dye tris(phenylpyridine)iridium. The D-EML system of two bipolar layers leads to an expansion of the exciton generation region. Due to its self-balancing character, accumulation of charge carriers at the outer interfaces is avoided. Thus, a power efficiency of approximately 77 lm∕W and an external quantum efficiency of 19.3% are achieved at 100 cd∕m2 with an operating voltage of only 2.65 V. More importantly, the efficiency decays only weakly with increasing brightness, and a power efficiency of 50 lm∕W is still obtained even at 4000 cd∕m2.
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85.60.Jb Light-emitting devices
85.60.Dw Photodiodes; phototransistors; photoresistors
72.20.Ee Mobility edges; hopping transport
71.35.Ee Electron-hole drops and electron-hole plasma
72.20.Fr Low-field transport and mobility; piezoresistance
78.60.Fi Electroluminescence
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